Diffusion tensor MR imaging in chronic spinal cord injury

BACKGROUND AND PURPOSE: Diffusion tensor MR imaging is emerging as an important tool for displaying anatomic changes in the brain after injury or disease but has been less widely applied to disorders of the spinal cord. The aim of this study was to characterize the diffusion properties of the entire human spinal cord in vivo during the chronic stages of spinal cord injury (SCI). These data provide insight into the structural changes that occur as a result of long-term recovery from spinal trauma.MATERIALS AND METHODS: Thirteen neurologically intact subjects and 10 subjects with chronic SCI (>4 years postinjury) were enrolled in this study. A single-shot twice-refocused spin-echo diffusion-weighted echo-planar imaging pulse sequence was used to obtain axial images throughout the entire spinal cord (C1-L1) in <60 minutes.RESULTS: Despite heterogeneity in SCI lesion severity and location, diffusion characteristics of the chronic lesion were significantly elevated compared with those of uninjured controls. Fractional anisotropy was significantly lower at the chronic lesion and appeared dependent on the completeness of the injury. Conversely, mean diffusivity measurements in the upper cervical spinal cord in subjects with SCI were significantly lower than those in controls. These trends suggest that the entire neuraxis may be affected by long-term recovery from spinal trauma.CONCLUSION: These results suggest that diffusion tensor imaging may be useful in the assessment of SCI recovery.

Diffusion tensor imaging (DTI) has been successfully used to characterize structural changes in neural tissue after spinal artery stroke,¹ multiple sclerosis,^2,3 cervical spondylotic myelopathy,⁴ spinal cord compression,⁵ and acute spinal cord injury (SCI)^6,7; however, DTI has not been used to explore the long-term changes in spinal cord structure known to accompany chronic SCI.^8–11 The purpose of this study was to characterize the diffusion values of the entire spinal cord in humans with chronic SCI (>4 years postinjury) by using a clinically available pulse sequence and comparing these data with normative DTI characteristics reported previously.¹² On the basis of previous work,¹³ we hypothesized that diffusion characteristics would be significantly altered throughout the entire length of the spinal cord.DTI research in SCI largely involves the use of experimental animal models to examine changes in diffusivity that accompany the early stages of injury. These studies have suggested overall diffusivity increases and diffusion anisotropy decreases near the injury site^14–18 due to axonal damage and/or vasogenic edema.¹⁵ Although a few studies have been conducted with human spinal cord pathologies,^4–7,19 they have also demonstrated an increase in diffusivity and a decrease in diffusion anisotropy.DTI may be useful for identifying the characteristics of chronic SCI, because structural changes in the spinal cord during the chronic stages may differ from the normal spinal cord and the spinal cord in acute stages of injury. For example, extensive longitudinal spreading of lesions in the late stages of injury creates widespread changes in the spinal cord morphology, including cyst formation and necrosis.²⁰ Changes in diffusivity associated with these structural alterations may make it possible to identify the rostral and caudal extent of a spinal lesion by using DTI. Many therapeutic interventions for rehabilitation after SCI, including functional electric stimulation²¹ and gait training,²² rely on intact spinal motoneurons below the level of the lesion. Incomplete injury in segments below the injury may be particularly difficult to identify by using physical or electrophysiologic measurements because sensory and motor function is often reduced or absent below the level of injury. Thus, DTI provides an opportunity to assess the integrity of the spinal cord.DTI might also be sensitive to changes in the structure of the spinal cord tissue in regions distant from the spinal lesion in chronic injury. Although the chronic stages of SCI are typically considered stable,^23,24 progressive demyelination in chronic SCI has been documented,^8–10 and remyelination, when it occurs, can result in significantly decreased myelin sheath thickness^8,25–27 and preferential loss of large-diameter axons.²⁶ Also, considerable atrophy of the spinal cord occurs in the late stages of SCI, causing the remaining axons to be compressed and tightly packed.¹¹ These changes could increase the attenuation of diffusion barriers, which would be consistent with the decrease in mean diffusivity recently reported in the upper cervical spinal cord rostral to the injury in a small number of subjects with chronic SCI.¹³Thus, the primary aim of this study was to characterize the diffusion properties across the entire spinal cord (C1–L1 vertebral levels) in humans with chronic SCI by using a clinically available DTI pulse sequence. We then compared these data with diffusion characteristics from a previously published young neurologically intact sample.¹²     

Diffusion tensor MR imaging of the neurologically intact human spinal cord

BACKGROUND AND PURPOSE: The aim of this study was to characterize the diffusion properties of the entire human spinal cord in vivo. These data are essential for comparisons to pathologic conditions as well as for comparisons of different pulse sequence design parameters aimed to reduce scan time and more accurately determine diffusion coefficients.MATERIALS AND METHODS: A total of 13 neurologically intact subjects were enrolled in this study. A single-shot, twice-refocused, spin-echo, diffusion-weighted, echo-planar imaging (EPI) pulse sequence was used to obtain axial images throughout the entire spinal cord (C1–L1) in 45 minutes.RESULTS: Diffusion images indicated slight geometric distortions; however, gray and white matter contrast was observed. All measurements varied across the length of the cord. Whole cord diffusion coefficients averaged 0.5–1.3 × 10⁻³ mm²/s depending on orientation, mean diffusivity (MD) averaged 0.83 ± 0.06 × 10⁻³ mm²/s, fractional anisotropy (FA) averaged 0.49 ± 0.05, and volume ratio (VR) averaged 0.73 ± 0.05.CONCLUSION: This study provided normative diffusion values for the entire spinal cord for use in comparisons with pathologic conditions as well as improvements in pulse sequence design.

Despite the potential of diffusion tensor imaging (DTI) for providing anatomic and histologic information about the spinal cord, DTI is not yet routinely performed for identifying and characterizing pathologic changes. One important limitation to the application of DTI to spinal cord pathologic disorders is the absence of normative data for comparison. For example, diffusion changes in the spinal cord have been reported after spinal artery stroke,¹ multiple sclerosis,² cervical spondylotic myelopathy,³ spinal cord compression,⁴ acute spinal cord injury,⁵ and chronic spinal cord injury,^6,7 yet detailed baseline data with use of common imaging sequences are lacking for comparison. Some diffusion measurements have been documented in targeted regions of the neurologically intact human spinal cord,^8–12 and these values have been used for comparison to pathologic conditions; however, a comprehensive study of diffusion parameters throughout the entire spinal cord has not been reported. As a result, the primary purpose of this study was to characterize the normative diffusion values of the entire human spinal cord with use of a clinically available pulse sequence for comparison with pathologic conditions and new pulse sequence designs.Current DTI research in the human spinal cord is primarily devoted to the development of pulse sequences aimed at obtaining artifact-free diffusion measurements. Single-shot echo-planar imaging (EPI) is relatively fast but is typically not used in the spinal cord because of the small size of the cord and the perceived risk for susceptibility-related distortions. Unfortunately, the main alternative to EPI, pulsed-gradient, spin-echo DTI, is highly sensitive to motion and has very long imaging times, requiring approximately 15 minutes to image a single diffusion axis.⁹ A few pulse sequences focus on a compromise between these 2 methods, including line scan diffusion imaging,¹³ multishot echo-planar imaging,¹⁰ and fast single-shot EPI with use of sensitivitiy encoding (SENSE).¹⁴ Although these new techniques have established a reputation for accurate diffusion measurements with minimal artifacts, they typically have low signal-to-noise ratio (SNR). A novel technique, presented by Bammer et al,^12,15 uses a phase-navigated interleaved EPI method to overcome SNR challenges; however, the technique is currently not available on MR scanners and thus has limited clinical usefulness.In contrast to recently developed DTI pulse sequences, single-shot EPI is widely available on clinical MR scanners; thus, diffusion-tensor (DT) EPI could serve as a standard for comparison of new pulse sequences. Previous studies involving single-shot DT EPI of the spinal cord have demonstrated its usefulness in estimating diffusion parameters within the spinal cord,^1,4,11,16 though a systematic study of the entire spinal cord has not been conducted. To establish baseline diffusion parameters for comparing new DTI sequences, we aimed to measure the DTI parameters and SNR of the entire spinal cord by using a single-shot, twice-refocused, spin-echo EPI diffusion sequence¹⁷ in the axial plane, with no respiratory or cardiac gating to image the entire spinal cord (C1–L1). We then compared the diffusion parameters from this DT EPI sequence with reported diffusion measurements that were obtained with a variety of recently developed pulse sequences to determine the agreement in diffusion parameters.Thus, the primary aim of this study was to characterize the diffusion properties of the human spinal cord in vivo with a single-shot DT EPI sequence to establish a baseline for clinicians to compare with measurements made in pathologic conditions. The secondary goal was to characterize the diffusion measurements from the current literature and determine if differences exist in mean diffusion characteristics across various pulse sequences and imaging platforms.     

Comparison of three different methods for measurement of cervical cord atrophy in multiple sclerosis

BACKGROUND AND PURPOSE: Evidence is mounting that spinal cord atrophy significantly correlates with disability in patients with multiple sclerosis (MS). The purpose of this work was to validate 3 different measures for the measurement of cervical cord atrophy on high-resolution MR imaging in patients with MS and in normal control subjects (NCs). We also wanted to evaluate the relationship between cervical cord atrophy and clinical disability in the presence of other conventional and nonconventional brain MR imaging metrics by using a unique additive variance regression model.MATERIALS AND METHODS: We studied 66 MS patients (age, 41.2 ± 12.4 years; disease duration, 11.8 ± 10.7 years; Expanded Disability Status Scale, 3.1 ± 2.1) and 19 NCs (age, 30.4 ± 12.0 years). Disease course was relapsing-remitting (34), secondary-progressive (14), primary-progressive (7), and clinically isolated syndrome (11). The cervical cord absolute volume (CCAV) in cubic millimeters and 2 normalized cervical cord measures were calculated as follows: cervical cord fraction (CCF) = CCAV/thecal sac absolute volume, and cervical cord to intracranial volume (ICV) fraction (CCAV/ICV). Cervical and brain lesion volume measures, brain parenchyma fraction (BPF), and mean diffusivity were also calculated.RESULTS: CCAV (P < .0001) and CCF (P = .007) showed the largest differences between NCs and MS patients and between different disease subtypes. In regression analysis predicting disability, CCAV was retained first (R² = 0.498; P < .0001) followed by BPF (R² = 0.08; P = .08). Only 8% of the variance in disability was explained by brain MR imaging measures when coadjusted for the amount of cervical cord atrophy.CONCLUSIONS: 3D CCAV measurement showed the largest differences between NCs and MS patients and between different disease subtypes. Cervical cord atrophy measurement provides valuable additional information related to disability that is not obtainable from brain MR imaging metrics.

MR imaging of the brain is a sensitive tool for making a diagnosis of multiple sclerosis (MS). Abnormalities of brain MR imaging are present in more than 95% of patients with clinically definite MS; however, there is poor correlation between disability and the number and volume of focal brain lesions visible on MR imaging.¹Involvement of the spinal cord, especially of the cervical cord,^2,3 is of particular significance in the development of physical disability in patients with MS.^4,5 During the course of their disease, approximately 80% of patients with MS present with spinal cord symptoms.⁶ Conventional T2-weighted spinal cord imaging is sensitive in detecting spinal cord lesions and their changes over time.^7,8 However, measures of cord T2 lesion number and volume failed to show a significant relationship with disability and have poor prognostic value for disability accumulation over the mid-to-long term.^2,3 Evidence is mounting that spinal cord atrophy significantly correlates with disability.^5,9–11Atrophy of the spinal cord in MS is thought to reflect inflammatory tissue injury, demyelination, and axonal loss. Postmortem pathologic studies have documented spinal cord axonal loss in MS.^12,13 However, whereas the correlation between central nervous system atrophy and disability has been interpreted as a reflection of axonal loss in pre-existing lesions,^14–16 axonal loss does not appear to directly affect the cross-sectional cord area in pathologic studies.² Measurement of spinal cord atrophy has demonstrated value in the clinical realm. Serial MR imaging of the spinal cord has shown evidence of disease activity undetectable on clinical examination, thereby increasing the diagnostic sensitivity of MR imaging for patients with suspected MS.¹⁷ Spinal cord abnormalities on MR imaging are not restricted only to patients presenting with spinal cord symptoms, because changes suggestive of atrophy may be seen before any manifestation of clinical symptoms. It has been shown that atrophy of the cervical spinal cord is a useful measure for determining clinical disability^10,15,18 and monitoring disease progression,¹⁹ as well as therapeutic drug effects in MS.²⁰Key problems in the evaluation of spinal cord atrophy have been related to poor resolution of MR imaging, small size of the cord, and surrounding fat, bone, and CSF that can cause artifacts and, as a consequence, compromise the final image quality. Indeed, artifacts related to pulsation and respiratory cardiac motion have also been considered.^2,3 This led in most of the earlier studies to unacceptable error in manual delineation of the cord/CSF interface.² The technical challenges of spinal cord imaging posed by the size and anatomy of the cord and by its surrounding structures have been addressed in recent years by improved receiver coils, fast imaging, 3D imaging, motion suppression, and cardiac gating. Subsequently, interest has emerged in a reproducible semiautomated measurement of the cord cross-sectional area²¹ and its improved measurement by reduction of partial volume effect,²² as well as by 3D extraction of the cord surface area.²³The goal of the present study was to investigate whether spinal cord atrophy in MS may be assessed by measurement of the whole cervical cord volume rather than by the traditional cross-sectional area approach at level C2/C3. To improve the accuracy and precision of cervical cord volume measurements, a semiautomated edge detection technique was used to create a tissue-boundary map from 3D volumetric scans of the cervical cord. Therefore, the objectives of the present cross-sectional study were first to validate this original method for measuring whole cervical cord volume by comparing 19 normal control subjects (NCs) and 65 patients with MS with different disease subtypes. We also evaluated the relationship between absolute and normalized cervical cord atrophy and clinical disability in the presence of other conventional and nonconventional brain MR imaging metrics using a unique additive variance regression model.     

Attenuation of lower-thoracic, lumbar, and sacral spinal cord motion: implications for imaging human spinal cord structure and function

BACKGROUND AND PURPOSE: Recent literature indicates that cervical and upper-thoracic spinal cord motion adversely affect both structural and functional MR imaging (fMRI; particularly diffusion tensor imaging [DTI] and spinal fMRI), ultimately reducing the reliability of these methods for both research and clinical applications. In the present study, we investigated motion of the lower-thoracic, lumbar, and sacral cord segments to evaluate the incidence of similar motion-related confounds in these regions.MATERIALS AND METHODS: Recently developed methods, used previously for measuring cervical and upper-thoracic spinal cord motion, were employed in the present study to examine anteroposterior (A/P) and left-right (L/R) spinal cord motion in caudal regions. Segmented cinematic imaging was applied with a gradient-echo, turbo fast low-angle shot (turbo-FLASH) pulse sequence to acquire midline images of the cord at 24 cardiac phases throughout the lower-thoracic, lumbar, and sacral spinal cord regions.RESULTS: The magnitude of A/P motion was found to be largest in rostral cord regions, whereas in caudal regions (at the level of the T4/T5 vertebrae and below), peak cord motion was uniformly small (routinely ≤0.10 mm). L/R motion, however, was found to be minimal throughout the thoracic, lumbar, and sacral regions.CONCLUSION: Motion-related errors in spinal fMRI and DTI are expected to be significantly reduced throughout caudal regions of the spinal cord, thus yielding higher sensitivity and specificity compared with rostral regions. The paucity of such errors is expected to provide a means of observing the specific impact of motion (in rostral regions) and to enable the acquisition of uncorrupted DTI and fMRI data for studies of structure and function throughout lumbar and sacral regions.

By virtue of their exquisite sensitivities to changes in neuronal activity and tissue microstructure, functional MR imaging (fMRI) and diffusion tensor imaging (DTI) possess significant potential as clinical tools for investigating spinal cord injury and assessing novel therapeutic strategies.^1–8 However, both of these techniques are highly sensitive to physiologic motion, and at this juncture, the effects of spinal cord motion and CSF flow are not yet fully known, primarily because of a lack of information regarding these complex, dynamic processes. Therefore, characterization of the normal 3D kinematics of spinal cord motion is imperative to the future development of spinal fMRI and DTI methods for research and clinical applications and to better understand and diagnose spinal cord injury and disease.Recent work has revealed a predictable, oscillatory pattern of cardiac-related spinal cord motion throughout the cervical and upper-thoracic cord regions, primarily in the rostral-caudal (R/C) and anteroposterior (A/P) directions (although there are slight intersubject variations, the cervical [C1–C8], thoracic [T1–T12], lumbar [L1–L5], and sacral [S1–S5] spinal cord segments correspond approximately with the C1–C7, T1–T10, T11–T12, and L1–L2 vertebral levels, respectively⁹).^10–15 Left-right (L/R) cord motion, on the other hand, appears to be evident only in a small subpopulation of individuals, and even in these cases, the amplitude of L/R motion is minimal.^10,15 Several independent reports have also speculated about the magnitude and character of motion-related confounds in spinal fMRI and DTI experiments, but only recently have studies been undertaken to elucidate the specific effects of spinal cord motion and the extent to which this will probably hinder spinal fMRI and DTI.^16–18 Motion-compensated analysis of spinal fMRI data has revealed that cord motion decreases both the sensitivity and selectivity to neuronal function in the cervical and upper-thoracic regions of the spinal cord.¹⁶ Likewise, for diffusion studies of rostral spinal cord segments, cardiac-gating at different time points of the heartbeat has revealed a strong dependence between the observed diffusion properties and cardiac phase.^17,18 Thus, there is strong evidence to suggest that accurate measurements of the mean diffusivity, fractional anisotropy, and principal eigenvector (ie, the size, shape, and orientation of the diffusion tensor) are all dependent on, and confounded by, the spinal cord motion occurring throughout the cervical and upper-thoracic cord regions.To improve spinal fMRI and DTI methods, a clear need emerges to characterize motion throughout the entire spinal cord, including the lower-thoracic, lumbar, and sacral regions. Improved methods for cervical and upper-thoracic spinal cord fMRI and DTI have already emerged as a result of establishing the patterns of cord motion in these regions.^16–18 Thus, our objective in the present study was to extend the characterization of cardiac-related A/P and L/R spinal cord motion to the thoracic, lumbar, and sacral spinal cord regions.     

Medulla oblongata volume: a biomarker of spinal cord damage and disability in multiple sclerosis

BACKGROUND AND PURPOSE: While brain MR imaging is routinely performed, the MR imaging assessment of spinal cord pathology in multiple sclerosis (MS) is less frequent in clinical practice. The purpose of this study was to determine whether measurements of medulla oblongata volume (MOV) on routine brain MR imaging could serve as a biomarker of spinal cord damage and disability in MS.MATERIALS AND METHODS: We identified 45 patients with MS with both head and cervical spinal cord MR imaging and 29 age-matched and sex-matched healthy control subjects with head MR imaging. Disability was assessed by the expanded disability status scale (EDSS) and ambulation index (AI). MOV and upper cervical cord volume (UCCV) were manually segmented; semiautomated segmentation was used for brain parenchymal fraction (BPF). These measures were compared between groups, and linear regression models were built to predict disability.RESULTS: In the patients, MOV correlated significantly with UCCV (r = 0.67), BPF (r = 0.45), disease duration (r = −0.64), age (r = −0.47), EDSS score (r = −0.49) and AI (r = −0.52). Volume loss of the medulla oblongata was −0.008 cm³/year of age in patients with MS, but no significant linear relationship with age was found for healthy control subjects. The patients had a smaller MOV (mean ± SD, 1.02 ± 0.17 cm³) than healthy control subjects (1.15 ± 0.15 cm³), though BPF was unable to distinguish between these 2 groups. MOV was smaller in patients with progressive MS (secondary- progressive MS, 0.88 ± 0.19 cm³ and primary-progressive MS, 0.95 ± 0.30 cm³) than in patients with relapsing-remitting MS (1.08 ± 0.15 cm³). A model including both MOV and BPF better predicted AI than BPF alone (P = .04). Good reproducibility in MOV measurements was demonstrated for intrarater (intraclass correlation coefficient, 0.97), interrater (0.79), and scan rescan data (0.81).CONCLUSION: MOV is associated with disability in MS and can serve as a biomarker of spinal cord damage.

Multiple sclerosis (MS) is a multifactorial disease with a strong neurodegenerative component associated with progressive atrophy of the brain and spinal cord.¹ Previous studies have shown involvement of the spinal cord in more than 80% of the patients with clinically definite MS.^2–5 Atrophy of the spinal cord is thought to originate mainly from neurodegenerative changes, especially of the cervical segment,^4,6–10 which results in impairment of motor function.^11–16 In contrast, brain atrophy correlates well with neuropsychologic impairment.¹ The most severe and debilitating physical disability in MS seems to be of spinal origin. Therefore, it has been suggested that measurements of upper spinal cord volume provides information regarding disease progression that is complementary to the assessment of brain atrophy.Although head MR imaging is routinely performed in patients with MS, spinal cord MR imaging takes additional time and is therefore performed only on specific indications, both in the clinic and research.The medulla oblongata is the most caudal part of the brain stem and is continuous with the spinal cord. It contains nuclei that are important for autonomic control such as respiration, heart rate, blood pressure and reflexes, and white matter (WM) tracts that connect the rostral and caudal parts of the central nervous system (CNS). Ventral, dorsal, and lateral funiculi in the lower medulla oblongata are continuous with those of the spinal cord.The medulla oblongata is generally included in the field of view (FOV) of routine brain MR images of patients with MS. We set out to explore the feasibility and clinical relevance of volumetric measures of the lower medulla oblongata and hypothesized that these measures will reflect spinal cord atrophy. The relative ease to obtain such measurements from routinely performed clinical MR imaging examinations of the head makes this a potentially strong candidate for a biomarker of spinal cord damage and disability. In this work we present the results of a retrospective analysis of MR imaging-derived medulla oblongata volume (MOV) in MS to establish the relationship to spinal cord, its correlation with clinical disability and the reproducibility of this metric.     

A T1 hyperintense perilesional signal aids in the differentiation of a cavernous angioma from other hemorrhagic masses

BACKGROUND AND PURPOSE: A cavernous angioma is a developmental vascular malformation with a high risk of hemorrhage. The purpose of this work was to retrospectively determine whether an MR sign of T1 hyperintense perilesional signal intensity is useful for the differentiation of cavernous angioma from other hemorrhagic cerebral masses.MATERIALS AND METHODS: The institutional review board approved this study. We retrospectively evaluated the MR images of 72 patients with acute or subacute cerebral hemorrhagic lesions with perilesional edema (29 cavernous angiomas, 13 glioblastomas, 1 oligodendroglioma, 16 metastatic tumors, and 13 intracerebral hemorrhages) for the presence of T1 hyperintense perilesional signal intensity. In addition, T1 signal intensities of a perilesional edema were quantitatively analyzed. In cavernous angiomas, volumes of hemorrhagic lesions and perilesional edemas, lesion locations, presence of contrast enhancement, and time intervals between symptom onset and MR imaging were also assessed. Data were analyzed using unpaired t test or Fisher exact test.RESULTS: T1 hyperintense perilesional signal intensity sign was found in 18 (62.1%) of 29 cavernous angiomas, in 1 (6.3%) of 16 metastases, and in 0 primary brain tumors or intracerebral hemorrhages. Sensitivity, specificity, and positive predictive value of this sign for cavernous angioma were 62%, 98%, and 95%, respectively. The perilesional T1 hyperintensity was significantly higher in cavernous angiomas (P = .045) than in normal white matter. Perilesional edema volumes were larger in cavernous angiomas with the MR sign than in cavernous angiomas without the sign (P = .009).CONCLUSION: When the MR sign of T1 hyperintense perilesional signal intensity is present, there is a high probability of cavernous angioma being present in the brain, and this MR sign may be helpful for differentiating cavernous angioma from hemorrhagic tumors and intracerebral hemorrhages.

A cavernous angioma, also known as a cavernous malformation or cavernoma, is a developmental vascular malformation that is typically a discrete multilobulated, berrylike lesion containing hemorrhage in various stages of evolution. Hemorrhage is a common complication of a cavernous angioma and is the cause of the first presentation in 30% of cases.^1,2 The reported annual risk of hemorrhage in a cavernous angioma varies widely (1%–6.8%).^3–5MR imaging is the most important diagnostic technique for the detection of cavernous angiomas and frequently produces highly characteristic images. Typically, cavernous angiomas show a mixed signal intensity core, a reticulated “popcorn ball” appearance, and a “T2 blooming sign,” which is due to a low signal intensity hemosiderin rim that completely surrounds the lesion.^6,7 Susceptibility-weighted imaging, such as a T2* gradient-echo image, is more useful for the detection of the hemosiderin deposit and the diagnosis of a cavernous angioma. The typical MR signs of “popcorn ball” appearance and “T2 blooming sign” on T2-weighted images have been reported to be found in approximately 50%–67% of cavernous angiomas.^2,8Based on these MR findings, although diagnosis is usually straightforward in typical cases of a cavernous angioma, lesions with unusual MR features may be misdiagnosed as primary or metastatic brain tumors.^9–18 The atypical MR features of cavernous angiomas include variable or strong enhancement,^2,9,10,19 a large perilesional vasogenic edema and mass effect,^2,10,19,20 the cystic form of a cavernous angioma,^9,20,21 and the manifestations of a recent hematoma.^22,23 Cavernous angiomas that present with recent hemorrhage and with a surrounding edema may mimic a primary or secondary brain tumor with hemorrhage; these lesions may be frequently underestimated as a sole hematoma.Recently, we encountered some cases that showed T1 hyperintensity in a perilesional edema around the acute or subacute hemorrhagic masses. As far as we know, the MR feature of T1 hyperintensity in a perilesional edema around a hemorrhagic mass has not yet been documented. The aim of this study was to determine in a retrospective study whether the MR sign of a T1 hyperintense perilesional signal intensity is useful for differentiating a cavernous angioma from other hemorrhagic cerebral masses.     

Diffuse pachymeningeal hyperintensity and subdural effusion/hematoma detected by fluid-attenuated inversion recovery MR imaging in patients with spontaneous intracranial hypotension

BACKGROUND AND PURPOSE: Fluid-attenuated inversion recovery (FLAIR) MR imaging has advantages to detect meningeal lesions. FLAIR MR imaging was used to detect pachymeningeal thickening and thin bilateral subdural effusion/hematomas in patients with spontaneous intracranial hypotension (SIH).MATERIALS AND METHODS: Eight patients were treated under clinical diagnoses of SIH. Chronologic MR imaging studies, including the FLAIR sequence, were retrospectively reviewed.RESULTS: Initial MR imaging showed diffuse pachymeningeal thickening as isointense in 6 cases, hypoisointense in 1 case, and isohyperintense in 1 case on the T1-weighted MR images, and hyperintense in all cases on both T2-weighted and FLAIR MR images. Dural (pachymeningeal) hyperintensity on FLAIR MR imaging had the highest contrast to CSF, and was observed as linear in all patients, usually located in the supratentorial convexity and also parallel to the falx, the dura of the posterior fossa convexity, and the tentorium, and improved after treatment. These characteristics of diffuse pachymeningeal hyperintensity on FLAIR MR imaging were similar to diffuse pachymeningeal enhancement (DPME) on T1-weighted imaging with gadolinium. Initial FLAIR imaging clearly showed subdural effusion/hematomas in 6 of 8 patients. The thickness of subdural effusion/hematomas sometimes increased transiently after successful treatment and resolution of clinical symptoms.CONCLUSION: Diffuse pachymeningeal hyperintensity on FLAIR MR imaging is a similar sign to DPME for the diagnosis of SIH but does not require injection of contrast medium. FLAIR is useful sequence for the detection of subdural effusion/hematomas in patients with SIH.

Spontaneous intracranial hypotension (SIH) syndrome is characterized by low CSF pressure and positional headache caused by leakage of spinal CSF.^1,2 MR imaging has revolutionized the identification, diagnosis, management, and understanding of SIH. The characteristic MR signs of SIH include diffuse pachymeningeal (dura mater) enhancement (DPME), bilateral subdural effusion/hematomas, downward displacement of the brain, enlargement of the pituitary gland, prominence of the spinal epidural venous plexus, engorgement of cerebral venous sinuses (“venous distension sign,” etc),³ venous sinus thrombosis,⁴ and isolated cortical vein thrombosis.⁵ DPME after gadolinium administration may be the most common and indicative sign^1,2 and forms the basis of the proposed “syndrome of orthostatic headache and diffuse pachymeningeal gadolinium enhancement.”⁶The cause of DPME remains unclear. Histologic examination of meningeal biopsy specimens consistently demonstrates a thin layer of fibroblasts as well as small, thin-walled, dilated blood vessels without evidence of inflammation on the subdural surface, the so-called dural border cell layer.⁷ These findings strongly suggest that dural venous dilation following the Monro-Kellie rule is the most likely explanation of DPME associated with SIH, which states that decreased CSF volume caused by CSF leakage requires volume compensation resulting in meningeal venous hyperemia and subsequent pachymeningeal enhancement.⁸ However, previous studies did not include detailed neuroradiologic evaluations of the pachymeninges in patients with SIH without artificial contrast materials to evaluate the transient and functional changes of the dura mater.⁹Bilateral subdural effusion/hematomas are also classic intracranial signs in the diagnosis of SIH, which again may be explained by the Monro-Kellie rule.^1,6,8 The incidence of subdural effusion/hematomas associated with SIH is 10% to 50% with use of conventional neuroradiologic techniques.^10,11 Subdural effusion/hematomas associated with SIH tend to be thin (typically 2–7 mm), do not cause appreciable mass effect, occur typically over the convexities of the brain, and appear as variable MR signal intensities depending on the fluid protein concentration or presence of blood.¹The fluid-attenuated inversion recovery (FLAIR) pulse sequence cancels the signal intensity from CSF and causes heavy T2 weighting because of the very long TE, resulting in excellent definition of anatomic detail, such as brain surface sulci, and high lesion contrast in areas close to the CSF.¹² This method is commonly used to detect meningeal lesions such as subarachnoid hemorrhage and meningitis.^13–15 Therefore, FLAIR MR imaging may be the optimum sequence to evaluate the thickened dura associated with SIH and to detect the very thin subdural effusion/hematomas located close to the subarachnoid CSF space.Our study used FLAIR MR imaging to examine the thickened dura and subdural effusion/hematomas in patients with SIH.     

Role of apparent diffusion coefficient values in differentiation between malignant and benign solitary thyroid nodules

BACKGROUND AND PURPOSE: Accurate imaging characterization of a solitary thyroid nodule has been clearly problematic. The purpose of this study was to evaluate the role of the apparent diffusion coefficient (ADC) values in the differentiation between malignant and benign solitary thyroid nodules.MATERIALS AND METHODS: A prospective study was conducted in 67 consecutive patients with solitary thyroid nodules who underwent diffusion MR imaging of the thyroid gland. Diffusion-weighted MR images were acquired with b factors of 0, 250, and 500 s/mm² by using single-shot echo-planar imaging. ADC maps were reconstructed. The ADC values of the solitary thyroid nodules were calculated and correlated with the results of histopathologic examination. Statistical analysis was performed.RESULTS: The mean ADC value of malignant solitary thyroid nodules was 0.73 ± 0.19 × 10⁻³ mm²/s and of benign nodules was 1.8 ± 0.27 × 10⁻³ mm²/s. The mean ADC values of malignant nodules were significantly lower than those of benign ones (P = .0001). There were no significant differences between the mean ADC values of various malignant thyroid nodules, but there were significant differences between the subtypes of benign thyroid nodules (P = .0001). An ADC value of 0.98 × 10⁻³ mm²/s was proved as a cutoff value differentiating between benign and malignant nodules, with 97.5%, 91.7%, and 98.9% sensitivity, specificity, and accuracy, respectively.CONCLUSION: The ADC value is a new promising noninvasive imaging approach used for differentiating malignant from benign solitary thyroid nodules.

Nodular thyroid is commonly detected on palpation in 4%–7% of the population,^1,2 on sonographic examination in 10%–40%, and by pathologic examination at autopsy in 50%.^3,4 In contrast, compared with the high prevalence of nodular thyroid disease, thyroid cancer is rare. The challenge of imaging thyroid nodules is to reassure most patients who have benign disease and to diagnose the minority of patients who will prove to have a malignancy.^5,6Ultrasonography has been used in the assessment of the thyroid nodules as a primary imaging technique.^2,7,8 Currently, there is no single sonographic criterion that can reliably distinguish benign from malignant thyroid nodules.^4,9 The results of predicting thyroid cancer with color Doppler sonography are controversial, with some reporting that Doppler sonography is helpful and others reporting that it did not improve diagnostic accuracy.^4,5,10,11 The hazards of radiation exposure are unavoidable in nuclear scintigraphy,² and not all functioning nodules on scintigraphy are benign.^6,9 The risk of cancer in a cold nodule is 4 times more common than in a hot nodule.^3,6 Fine-needle aspiration biopsy (FNAB) with cytologic evaluation is commonly used, but it is inconclusive in 15%–20% of patients, in addition to the possible, but less likely, associated hemorrhage.^2,4 The incidence of cancer in patients with thyroid nodules selected for FNAB is approximately 9.2%–13%.⁵ FNAB is considered an effective method for differentiating between benign and malignant thyroid nodules.^4,7,12–14Routine T1- and T2-weighted MR imaging has a limited role in the evaluation of thyroid nodules. It cannot distinguish benign from malignant nodules or assess the functional status of thyroid nodules.^12–15 Diffusion-weighted MR imaging has been used to characterize head and neck tumors, in which there are significant differences in the apparent diffusion coefficient (ADC) values of malignant tumors and benign lesions.^16–19 Tezuka et al,²⁰ in their study using diffusion-weighted MR imaging to assess the thyroid function, reported that the ADC values of patients with Grave''s disease exceeded those of patients with subacute thyroiditis, with a sensitivity and specificity of 75% and 80%, respectively, in differentiating between both disease entities. They concluded that diffusion-weighted MR imaging could be clinically important in evaluating the thyroid function. To our knowledge, there have been no articles about diffusion-weighted MR imaging evaluating thyroid nodules.The aim of our study was to evaluate the role of ADC values in differentiating between malignant and benign solitary thyroid nodules.     

Sinonasal organized hematoma: CT and MR imaging findings

BACKGROUND AND PURPOSE: Sinonasal organized hematoma (OH) is an uncommon, nonneoplastic benign condition that can be locally aggressive. The purpose of this work was to characterize the CT and MR imaging findings of sinonasal OH.MATERIALS AND METHODS: CT (n = 11) and MR (n = 10) images of 12 patients (9 men and 3 women; mean age, 41 years; range, 12–76 years) with pathologically proved sinonasal OH were retrospectively reviewed. Particular attention was put on the location, shape, size, extent, internal architecture, and enhancement pattern of the lesion and associated sinus wall change.RESULTS: The lesions were seen as an expansile (n = 9) or nonexpansile (n = 3) mass, ranging in size from 2.2 to 6.0 cm (mean, 4.2 cm), primarily involving the maxillary sinus (n = 11) or nasal cavity (n = 1) unilaterally. The ipsilateral nasal cavity was also involved in 9 of 11 maxillary sinus lesions. Smooth sinus wall erosion other than the medial maxillary sinus wall was noted in 8 lesions. The internal architecture was best displayed on T2-weighted MR images on which all of the lesions were seen as a mixture of marked heterogeneous hypointensity and isointensity, surrounded by a hypointense peripheral rim, reflecting histologic heterogeneity of the lesion composed of hemorrhage, fibrosis, and neovascularization. Marked irregular nodular, papillary, or frondlike enhancement at the areas of neovascularization was also a typical finding seen in all of the lesions.CONCLUSION: An expansile soft tissue mass, smooth sinus wall erosion, marked heterogeneous signal intensity with a hypointense peripheral rim on T2-weighted MR images, and marked irregular nodular, papillary, or frondlike enhancement are characteristic CT and MR imaging findings of sinonasal OH.

Sinonasal organized hematoma (OH) is an uncommon, nonneoplastic benign condition that can be locally aggressive. Without careful evaluation of all of the imaging features, this may be mistaken for a malignant lesion both clinically and radiologically. It most commonly affects the maxillary sinus and can result from various causes of hemorrhage with chronic hematoma formation, followed by the process of organization through fibrosis and neovascularization.^1,2 Since the first report by Ozhan et al³ in a patient with von Willebrand disease, only fewer than 40 cases have been reported in the English literature under various names, including pseudotumor,^3,4 hematoma,⁵ organized or organizing hematoma,^1,2,6–8 and hematoma-like mass of the maxillary sinus.⁹Correct preoperative diagnosis of sinonasal OH is important to avoid unnecessary extensive surgery, because this condition is curative with a simple, conservative surgical approach and rarely recurs. Although there have been a few reports on the CT findings of sinonasal OH,^1–3,5–9 which are reported to be rather nonspecific, to our knowledge, the MR imaging features have not systematically been analyzed previously. Only 2 studies had briefly mentioned the MR imaging features.^8,9 Yagisawa et al⁹ reported that masses were well demarcated from the surrounding structures and heterogeneous in signal intensity on both T1- and T2-weighted MR images. Song et al⁸ reported that the lesions appeared as isosignal intensity with a margin that had a slightly higher signal intensity on T1-weighted images and a mosaic of various signal intensities and a low signal intensity rim on T2-weighted images. The purpose of this study was to report the CT and MR imaging findings, which are believed to be characteristic for sinonasal OH.     

Can MR Imaging Diagnose Adult-Onset Alexander Disease?

BACKGROUND AND PURPOSE: In recent years, the discovery that mutations in the glial fibrillary acidic protein gene (GFAP) were responsible for Alexander disease (AD) brought recognition of adult cases. The purpose of this study was to demonstrate that MR imaging allows identification of cases of AD with adult onset (AOAD), which are remarkably different from infantile cases.MATERIALS AND METHODS: In this retrospective study, brain and spinal cord MR imaging studies of 11 patients with AOAD (7 men, 4 women; age range, 26–64 years; mean age, 43.6 years), all but 1 genetically confirmed, were reviewed. Diffusion and spectroscopic investigations were available in 6 patients each.RESULTS: Atrophy and changes in signal intensity in the medulla oblongata and upper cervical spinal cord were present in 11 of 11 cases and were the diagnostic features of AOAD. Minimal to moderate supratentorial periventricular abnormalities were seen in 8 patients but were absent in the 3 oldest patients. In these patients, postcontrast enhancement was also absent. Mean diffusivity was not altered except in abnormal white matter (WM). Increase in myo-inositol (mIns) was also restricted to abnormal periventricular WM.CONCLUSIONS: Awareness of the MR pattern described allows an effective selection of the patients who need genetic investigations for the GFAP gene. This MR pattern even led to identification of asymptomatic cases and should be regarded as highly characteristic of AOAD.

Up to a few years ago, Alexander disease (AD) was known as a rare, genetically determined leukoencephalopathy affecting infants and children, characterized by macrocephaly, seizures, spasticity, and retarded psychomotor development, and leading to death in 2 months to 7 years.¹ The diagnostic MR imaging features established by van der Knaap et al² consisted of extensive white matter (WM) increased signal intensity on T2-weighted images, mainly in the frontal regions; a rim of periventricular T2 hypointensity; involvement of the basal ganglia, thalami, and brain stem; and postcontrast enhancement in the periventricular regions and scattered areas of the brain stem. These features allowed the diagnosis without biopsy, which was performed in the search for Rosenthal fibers, the histologic hallmark of the disease.^2,3Milder forms with spastic paraparesis, ataxia, or lower brain stem signs and juvenile (2–12 years of age) or adult onset (≥13 years) had been diagnosed as AD at postmortem examination because of the presence of Rosenthal fibers.⁴ After 2001, the discovery that mutations in the glial fibrillary acidic protein gene (GFAP) were responsible for the disease^5,6 allowed recognition during life of juvenile or adult forms^1,7–20 that have an MR imaging pattern remarkably different from that observed in children, with predominant focal involvement of the lower brain stem.In the last 4 years, on the basis of the MR imaging findings, we suggested the diagnosis of adult-onset AD (AOAD) in 11 patients, all but one genetically confirmed, and were struck by the constant involvement of the medulla oblongata and upper spinal cord. Therefore, we have analyzed retrospectively the imaging studies to verify the reliability of MR in making the diagnosis. The results of the genetic studies are also briefly reported.     

Combined 3T diffusion tensor tractography and 1H-MR spectroscopy in motor neuron disease

BACKGROUND AND PURPOSE: Diagnostic confidence in motor neuron disease may be improved by the use of advanced MR imaging techniques. Our aim was to assess the accuracy (sensitivity/specificity) and agreement of combined ¹H-MR spectroscopy (proton MR spectroscopy) and diffusion tensor imaging (DTI) at 3T in patients with suspected motor neuron disease regarding detection of upper motor neuron (UMN) dysfunction.MATERIALS AND METHODS: Eighteen patients with suspected motor neuron disease were studied with MR spectroscopy/DTI and clinically rated according to the El-Escorial and ALSFRS-R scales. For MR spectroscopy, absolute N-acetylaspartate (NAA), choline (Cho), and phosphocreatine (PCr) concentrations and relative NAA/Cho and NAA/PCr ratios of corresponding volumes of interest within the primary motor cortex were calculated. For DTI, fractional anisotropy (FA) and mean diffusivity (MD) were measured bilaterally at the level of the precentral gyrus, corona radiata, internal capsule, cerebral peduncles, pons, and pyramid. FA and MD statistics were averaged on the corticospinal tracts (CSTs) as a whole to account for a region-independent analysis.RESULTS: MR spectroscopy indicated NAA reduction beyond the double SD of controls in 6 of 8 patients with clinical evidence for UMN involvement. Congruently, the mean FA of these patients was significantly lower in the upper 3 regions of measurements (P < .01). Overall, MR spectroscopy and DTI were concordant in all except 3 cases: 1 was correctly excluded from motor neuron disease by DTI (genetically proved Kennedy syndrome), whereas MR spectroscopy indicated CST involvement. MR spectroscopy and DTI each were false-positive for CST affection in 1 patient with lower motor neuron involvement only.CONCLUSION: Combined MR spectroscopy/DTI at 3T effectively adds to the detection of motor neuron disease with a high degree of accordance.

Amyotrophic lateral sclerosis (ALS), Lou Gehrig syndrome or Charcot disease, is the most common progressive motor neuron disease.¹ Classic ALS affects the upper (UMN) and lower motor neurons (LMN), but cases with predominant UMN or LMN involvement also occur. It is still debated whether primary lateral sclerosis (PLS) and ALS are distinct disorders or manifestations of a single disorder, and a classification into ALS, UMN–dominant ALS, and PLS has been proposed to systematize future trials,² hence the correctness of UMN assessment is crucial.In addition to traditional diagnostic steps, such as electromyography, transcranial magnetic stimulation,^3,4 and assessment according to established clinical rating scales (eg, El-Escorial [EE]⁵ or ALS Functional Rating Scale-Revised [ALSFRS-R⁶]), recent promising attempts to improve diagnostic confidence of UMN assessment used advanced MR imaging techniques: ¹H-MR spectroscopy (proton MR spectroscopy),^7–11 diffusion tensor imaging (DTI),^12–19 diffusion tensor tractography (DTT),²⁰ or combinations thereof.^21,22 However, systematic evaluation of their concordance in the same patients is still rare.^21,23To obtain a definite diagnosis early in the disease is important for therapeutic intervention,^21,24 quality of life,^17,25,26 and monitoring therapeutic trials.^16,22 Cervical myelopathy, Kennedy syndrome (spinobulbar muscle atrophy, [SBMA]), peripheral nerve lesions, and multifocal polyneuropathy are, among others, differential diagnoses that have to be excluded. The clinical diagnosis is especially difficult when UMN involvement remains unclear. The previously mentioned techniques not only hold the promise of a more specific and potentially objective MR imaging measure but may even lead to a biomarker of disease severity.In contrast, most characteristics observed on structural MR imaging, such as corticospinal tract (CST) hyperintensities in T2-weighted, proton density, and fluid-attenuated inversion recovery (FLAIR) imaging^27–32; hypointense precentral gyrus changes^33,34; or marked frontal or callosal atrophy,³⁵ are rather uncertain.^31,32 CST hyperintensities are frequently found in healthy individuals, whereas the hypointense precentral gyrus sign apparently is motor neuron disease–specific according to Ishikawa et al³³ but occurs only in a minority of patients with ALS. To our knowledge, none of these signs have yet been studied at 3T. The principal aim of the present study was to evaluate the diagnostic accuracy of combined MR spectroscopy and DTI at 3T as an additional diagnostic tool in patients with suggested motor neuron disease and to provide an estimate of their concordance when applied to the same patients.     

Preoperative grading of presumptive low-grade astrocytomas on MR imaging: diagnostic value of minimum apparent diffusion coefficient

BACKGROUND AND PURPOSE: Histopathologic grade of glial tumors is inversely correlated with the minimum apparent diffusion coefficient (ADC). We assessed the diagnostic values of minimum ADC for preoperative grading of supratentorial astrocytomas that were diagnosed as low-grade astrocytomas on conventional MR imaging.MATERIALS AND METHODS: Among 118 patients with astrocytomas (WHO grades II–IV), 16 who showed typical MR imaging findings of low-grade supratentorial astrocytomas on conventional MR imaging were included. All 16 patients underwent preoperative MR imaging and diffusion-weighted imaging. The minimum ADC value of each tumor was determined from several regions of interest in the tumor on ADC maps. To assess the relationship between the minimum ADC and tumor grade, we performed the Mann-Whitney U test. A receiver operating characteristic (ROC) analysis was used to determine the cutoff value of the minimum ADC that had the best combination of sensitivity and specificity for distinguishing low- and high-grade astrocytomas.RESULTS: Eight of the 16 patients (50%) were confirmed as having high-grade astrocytomas (WHO grades III and IV), and the other 8 patients were confirmed as having low-grade astrocytomas (WHO grade II). The median minimum ADC of the high-grade astrocytoma (1.035 × 10⁻³ mm² · sec⁻¹) group was significantly lower than that of the low-grade astrocytoma group (1.19 × 10⁻³ mm² · sec⁻¹) (P = .021). According to the ROC analysis, the cutoff value of 1.055 × 10⁻³ mm² · sec⁻¹ for the minimum ADC generated the best combination of sensitivity (87.5%) and specificity (79%) (P = .021).CONCLUSION: Measuring minimum ADC can provide valuable diagnostic information for the preoperative grading of presumptive low-grade supratentorial astrocytomas.

Despite aggressive treatments, overall prognosis of high-grade astrocytomas, especially glioblastomas, is still poor, mainly due to their infiltrative nature and high relapse rate compared with those of low-grade astrocytomas.^1–4 Accurate preoperative grading of a brain tumor is thus pivotal in choosing the treatment strategy and in the assessment of prognosis.On conventional MR imaging, malignant gliomas usually show strong contrast enhancement, peritumoral edema, mass effects, heterogeneity, central necrosis, and intratumoral hemorrhage. The typical MR imaging features of low-grade astrocytomas include a relatively well-defined usually homogeneous mass that displays little or no mass effect, with minimal or no vasogenic edema and little or no enhancement after contrast administration.^5–7 Nevertheless, it is not always easy to differentiate low-grade astrocytomas from high-grade ones on the basis of conventional MR imaging findings. It has been reported that high-grade and low-grade astrocytomas can have overlapping features on MR imaging.^2,8–12 Recently, it was shown that the histopathologic grade of glial tumors is inversely correlated with the minimum apparent diffusion coefficient (ADC).^1,3,9,13,14 Thus, we hypothesized that a high-grade astrocytoma may demonstrate a lower minimum ADC value even though it shows the typical MR imaging features of low-grade gliomas.The purpose of this study was to evaluate the diagnostic value of the minimum ADC for preoperative histopathologic grading in supratentorial astrocytomas that showed typical features of low-grade astrocytomas on conventional MR imaging.     

Nontraumatic skull base defects with spontaneous CSF rhinorrhea and arachnoid herniation: imaging findings and correlation with endoscopic sinus surgery in 27 patients

BACKGROUND AND PURPOSE: Defects at the skull base leading to spontaneous CSF rhinorrhea are rare lesions. The purpose of our study was to correlate CT and MR findings regarding the location and content of CSF leaks in 27 patients with endoscopic sinus surgery observations.MATERIALS AND METHODS: Imaging studies in 27 patients with intermittent CSF rhinorrhea (CT in every patient including 10 examinations with intrathecal contrast, plain CT in 2 patients, and MR in 15 patients) were analyzed and were retrospectively blinded to intraoperative findings.RESULTS: CT depicted a small endoscopy-confirmed osseous defect in 3 different locations: 1) within the ethmoid in 15 instances (53.6% of defects) most commonly at the level of the anterior ethmoid artery (8/15); 2) adjacent to the inferolateral recess of the sphenoid sinus in 7 patients including one patient with bilateral lesions (8/28 defects, 28.6%); 3) within the midline sphenoid sinus in 5 of 28 instances (17.9%). Lateral sphenoid defects (3.5 ± 0.80 mm) were larger than those in ethmoid (2.7 ± 0.77 mm, P ≤ 0.029) or midsphenoid location (2.4 ± 0.65 mm, P ≤ 0.026). With endoscopy proven arachnoid herniation in 24 instances as reference, MR was correct in 14 of 15 instances (93.3%), CT cisternography in 5 of 8 instances (62.5%). Plain CT in 1 patient was negative.CONCLUSION: In patients with a history of spontaneous CSF rhinorrhea, CT was required to detect osseous defects at specific sites of predilection. MR enabled differentiating the contents of herniated tissue and allowed identification of arachnoid tissue as a previously hardly recognized imaging finding.

The term “spontaneous” CSF rhinorrhea has been applied to describe nasal discharge of CSF unrelated to trauma, surgery, malformation, tumor, or previous radiation therapy.^1–4 Spontaneous CSF rhinorrhea is uncommon. Estimates of the spontaneous cause among all causes of CSF rhinorrhea are subject to variation ranging from only 6%,⁵ 11.4%,⁶ 14%,³ 21%,⁷ to 23%.⁸ Periodic release of CSF from the nose was first described by Galen in 200 B.C. and was considered a physiologic phenomenon until Thomson, in 1899, assembled 21 patients in a monograph reporting spontaneous CSF rhinorrhea as a pathologic clinical entity.^9,10Spontaneous CSF rhinorrhea has been recognized as a distinct entity with respect to clinical presentation,^2,11,12 treatment,^13–15 and propensity for recurrence.^8,16,17 As early as 1968, Ommaya et al⁹ postulated the existence of “high-pressure leaks” related to intracranial tumors and of “normal pressure leaks” occasionally associated with empty sella. The role of empty sella as an indicator of raised intracranial pressure as well was supported by the observation of elevated CSF pressure in individual patients¹¹ and in a series of 10 patients who underwent lumbar puncture after sealing of the defect.¹⁸ In addition to the presence of an empty sella as a radiologic sign,¹⁹ a common clinical constellation in patients with spontaneous CSF rhinorrhea is female sex, middle age, and obesity.^{8,14,15,18–22}Spontaneous CSF leaks have been postulated to represent a manifestation of benign intracranial hypertension²² or pseudotumor cerebri.²³ Pulsatile-increased hydrostatic pressure is capable of bone erosion during the course of many years.^2,24 To become effective as a CSF leak, bone erosion and creation of an osteodural defect is required to occur at pneumatized parts of the skull base leading to communication of the subarachnoid space with the sinonasal spaces or temporal bone cavity. Related to CSF rhinorrhea, a review of the literature up to 1972¹⁰ identified the cribriform plate, craniopharyngeal canal, sella, and spheno-occipital synchondrosis as possible sites of predilection. Arachnoid granulations in proximity to the ethmoid and sphenoid sinus have been implicated as precursors of osteodural leaks.² Accordingly, arachnoid granulations causing erosion of the temporal bone may present with CSF otorrhea.^2,25,26Among the imaging techniques used to localize the site of the fistula, radionuclide isotope cisternography and CT cisternography were of limited sensitivity in 66% of patients only.³ When active leaks were present, CT cisternography provided positive results in 85% of patients.²⁷ However, in cases of inactive fistulas, CT cisternography failed to recognize the site of leakage in 27.7%²⁸ and in 19% of patients.²⁹ Advances in CT and MR imaging techniques have improved sensitivity, which amounted to 88.25%³⁰ and 93%³¹ for high-resolution CT and for MR cisternography to 89%,^6,31 93.6%,²⁸ and 100%^32,33 even in patients with inactive leaks. Therefore, high-resolution CT, MR cisternography, or a combination of both techniques have replaced the previously used invasive procedures.A confounding nomenclature exists regarding the contents of osteodural defects such as meningocele,^10,14 meningoencephalocele,⁴ encephalocele,^11,34 meningeal or arachnoid hernia,^24,35 arachnoid diverticulum,³⁶ or arachnoid cyst.³⁷ These differing designations reflect variable contents of herniation and occasional inaccuracy because of the limited ability to visualize the lesions by imaging^24,29 and during transcranial surgery.^1,10 Knowledge of the contents of herniation may modify the grafting technique and therefore facilitates preoperative planning.¹⁶ The endoscopic skull base approach has rendered direct visualization of the defect and its contents feasible.^38–40 Therefore, endoscopy was chosen as a standard of reference in this study. CT and MR findings in this series of patients with spontaneous CSF rhinorrhea were particularly assessed regarding the contents of herniation and location and correlated with endoscopy. Predisposing factors (arachnoid granulation, empty sella) and the size of the osseous defect were assessed on CT images.     

Posterior reversible encephalopathy syndrome after solid organ transplantation

BACKGROUND AND PURPOSE: Posterior reversible encephalopathy syndrome (PRES) is known to occur after solid organ transplantation (SOT), potentially associated with cyclosporine and tacrolimus. In this study, we assess the frequency and clinical and imaging characteristics of PRES after SOT.MATERIALS AND METHODS: We identified 27 patients (13 men and 14 women; age range, 22–72 years) who developed PRES after SOT. Features noted included SOT subtype, incidence and timing of PRES, infection and rejection, mean arterial pressure (MAP), and toxicity brain edema.RESULTS: PRES developed in 21 (0.49%) of 4222 patients who underwent transplantation within the study period (no significant difference among SOT subtypes). Transplantation was performed in 5 patients before the study period, and 1 patient underwent transplantation elsewhere. In consideration of all 27 patients, PRES typically developed in the first 2 months in patients who had SOT of the liver (9 of 10 patients) and was associated with cytomegalovirus (CMV), mild rejection, or systemic bacterial infection. PRES also typically developed after 1 year in patients who had SOT of the kidney (8 of 9 patients) and was associated with moderate rejection or bacterial infection. Toxicity MAP was significantly lower (P < .001) in liver transplants (average MAP, 104.8 ± 16 mm Hg) compared with that in kidney transplants (average MAP, 143 ± 20 mm Hg). Toxicity brain edema was significantly greater (P < .001) in patients who had liver transplants and developed PRES compared with patients who had undergone kidney transplants despite severe hypertension in those who had the kidney transplants.CONCLUSION: Patients who had undergone SOTs have a similar low incidence of developing PRES. Differences between those who have had liver and kidney transplants included time after transplant, toxicity MAP, and PRES vasogenic edema noted at presentation. In patients who have undergone kidney transplants, severely elevated MAP was associated with reduced, not greater, brain edema.

Neurotoxicity with the development of the posterior reversible encephalopathy syndrome (PRES) imaging pattern is most typically noted in solid organ transplantation (SOT), allogeneic bone marrow transplantation (allo-BMT), and eclampsia.^1–17 PRES is also seen in association with infection, sepsis, shock, autoimmune disease, and after chemotherapy.^18–27 Patients develop headache, visual disturbance, or altered mentation, which often progress to seizure.²⁸ Severe hypertension is commonly present, but patients may be normotensive (20% to 30%).^3,29,30On CT or MR imaging, vasogenic edema is typically present in the occipital and parietal regions but also in the frontal lobes (in particular, along the superior frontal sulcus), inferior temporo-occipital junction, and cerebellar hemispheres.^1,3,18,19,31 Involvement of the deep white matter (WM), basal ganglia, and brain stem is also seen, with areas of restricted diffusion and focal hemorrhage occasionally noted.^4,6,31Although many case reports have described PRES or cyclosporine and tacrolimus neurotoxicity in SOT, to our knowledge, a comprehensive assessment has not been performed. The purpose of this retrospective study was to evaluate the incidence of PRES after SOT along with the clinical and imaging features of PRES neurotoxicity in a large population of patients who have undergone SOT.     

Extent of microstructural white matter injury in postconcussive syndrome correlates with impaired cognitive reaction time: a 3T diffusion tensor imaging study of mild traumatic brain injury

BACKGROUND AND PURPOSE: Diffusion tensor imaging (DTI) may be a useful index of microstructural changes implicated in diffuse axonal injury (DAI) linked to persistent postconcussive symptoms, especially in mild traumatic brain injury (TBI), for which conventional MR imaging techniques may lack sensitivity. We hypothesized that for mild TBI, DTI measures of DAI would correlate with impairments in reaction time, whereas the number of focal lesions on conventional 3T MR imaging would not.MATERIALS AND METHODS: Thirty-four adult patients with mild TBI with persistent symptoms were assessed for DAI by quantifying traumatic microhemorrhages detected on a conventional set of T2*-weighted gradient-echo images and by DTI measures of fractional anisotropy (FA) within a set of a priori regions of interest. FA values 2.5 SDs below the region average, based on a group of 26 healthy control adults, were coded as exhibiting DAI.RESULTS: DTI measures revealed several predominant regions of damage including the anterior corona radiata (41% of the patients), uncinate fasciculus (29%), genu of the corpus callosum (21%), inferior longitudinal fasciculus (21%), and cingulum bundle (18%). The number of damaged white matter structures as quantified by DTI was significantly correlated with mean reaction time on a simple cognitive task (r = 0.49, P = .012). In contradistinction, the number of traumatic microhemorrhages was uncorrelated with reaction time (r = −0.08, P = .71).CONCLUSION: Microstructural white matter lesions detected by DTI correlate with persistent cognitive deficits in mild TBI, even in populations in which conventional measures do not. DTI measures may thus contribute additional diagnostic information related to DAI.

Traumatic brain injury (TBI) is the leading cause of death and disability in young people, with 1.4 million annually reported cases in the United States and an estimated 57 million people worldwide hospitalized with 1 or more TBIs.¹ Furthermore, approximately 80% of the hospital-reported patients with TBI are categorized as having mild TBI on the basis of a Glasgow Coma Scale score between 13 and 15. Although those patients with mild TBI with normal CT findings and no post-traumatic amnesia usually have complete resolution of post-traumatic symptoms within 1 month, approximately 30% of patients with mild TBI with posttraumatic amnesia have persistent posttraumatic symptoms, and a significant number at 1-year postinjury have decreased functional outcome.^2,3Structural imaging studies of acute TBI demonstrate that MR imaging is more sensitive than CT in the number of traumatic lesions visualized.⁴ However, the relationship between focal structural lesions detected by conventional MR imaging and long-term patient outcome is controversial.^3,5-7 Nevertheless, patients with TBI with posttraumatic symptoms often have cognitive impairment, and their cognitive function is a major predictor of poor outcome.^8-12 In particular, attention, working memory, cognitive manipulation of temporal information, and processing speed are vulnerable.^13,14 Sequelae of TBI cause significant disability, which compelled the National Institutes of Health (NIH) to declare mild TBI as a major public health problem.¹⁵Although conventional MR imaging techniques can readily visualize posttraumatic focal structural lesions, they fail to adequately detect diffuse axonal injury (DAI), the key mechanism of damage following TBI.¹⁶ DAI results from unequal rotational or acceleration/deceleration forces that cause multifocal lesions in white matter due to a shear-strain deformation.^17-19 DAI is primarily responsible for transient deficits in cognitive performance in domains such as processing speed, working memory, and attention.^20,21 More recent studies suggest that DAI causes persistent postconcussive symptoms in executive function and memory dysfunction.^8,22-25MR diffusion tensor imaging (DTI) may be used to better assess DAI. In DTI, the characteristics of water diffusion in the brain are used to assess microstructural integrity of white matter pathways.²⁶ In white matter, water diffuses more readily along the orientation of axonal fibers than across the fibers due to hindrance from structural elements such as the axolemma and the myelin sheath. One can calculate the apparent diffusion coefficient (ADC), which is a rotationally invariant measure of the magnitude of diffusion. The degree of directionality of diffusion is termed “anisotropy.” This is the variation in the eigenvalues of the diffusion tensor.²⁷ Fractional anisotropy (FA), a normalized measure of anisotropy, has been shown to be sensitive to microstructural changes in white matter integrity.^28,29 Such measurements quantify the extent of damage following TBI^24,30-32 and are more sensitive than conventional MR imaging to axonal injury in a mouse model of TBI.³³In a group of patients with mild TBI with persistent postconcussive symptoms, we tested the hypothesis that the extent of microstructural white matter injury on DTI would account for deficits in cognitive reaction time, whereas the number of focal lesions on conventional MR imaging would not. The purpose of this study was to determine the predominant areas of damage in mild TBI and whether the spatial extent of white matter injury on DTI can be used as an effective biomarker for global cognitive outcome.     

Incidental acute infarcts identified on diffusion-weighted images: a university hospital-based study

BACKGROUND AND PURPOSE: Pathogenesis of leukoaraiosis is incompletely understood and accumulation of small infarctions may be one of the possible sources of such white matter lesions. Thus, the purpose of this study was to identify the rate of incident infarction as depicted on diffusion-weighted images (DWIs) obtained from a general patient population.MATERIALS AND METHODS: During the 4-year study period, a total of 60 patients (36 men and 24 women) had an incidental DWI-defined infarction without overt clinical symptoms suggestive of a stroke or a transient ischemic attack. All of the MR images were obtained by using a similar protocol on 2 identical 1.5T whole-body scanners. The patient''s vascular risk factors, as well as the presence of white matter lesions (WMLs) on MR imaging and atheromatous changes on MR angiography, were assessed retrospectively. The incidental DWI-defined infarcts were also characterized in terms of their lateralization, lobe, and specific location.RESULTS: A total of 16,206 consecutive brain MR images were done during the study period; the overall incidence of incidental infarcts was 0.37%. Most of these patients with an incidental infarct had vascular risk factors and WMLs on MR images. Most of these patients (80%) had a single lesion on DWI. A total of 88 lesions were identified; most were located in the white matter of the supratentorial brain, primarily in the frontoparietal lobes. There were also lesions involving the brain stem (n = 2). The lesions involving cerebrum were more commonly located in the right side (right to left = 52:34).CONCLUSION: Small, DWI-defined acute brain infarctions can be found incidentally in an asymptomatic population; this finding may account, at least in part, for the pathogenesis of WMLs identified on MR imaging.

White matter lesions depicted on MR imaging have been a center of debate for many years. These white matter rarefactions were originally described on CT and termed “leukoaraiosis” by Hachinski et al.¹ Epidemiologic studies have shown that leukoaraiosis is correlated with age, hypertension (HT), and arteriosclerosis.^2-6 Other reported causative factors include cigarette smoking⁶ and glucose intolerance.⁵ These predisposing factors are also found in patients with lacunar infarcts; thus, it has been proposed that leukoaraiosis and symptomatic lacunar infarcts share a similar underlying vasculopathy, namely, subcortical occlusive small-vessel disease secondary to arteriolosclerosis.^7-9Population studies have noted that leukoaraiosis progresses over a period of years.^6,10 The mechanism by which these lesions increase over time remains unknown. It has also not been determined whether a new white matter lesion (WML) focus grows slowly over a period of months or whether it suddenly appears and evolves rapidly as an acute infarct. Previously proposed mechanisms include both insidious and acute processes.^11-17 For instance, one of the proposed insidious mechanisms is apoptosis induced by chronic ischemia.¹⁴ Microembolic events have been proposed as an acute pathogenetic process.^15,16 Other proposed etiologies, which could be either insidious or acute, include intermittent changes in cerebral perfusion pressure resulting in incomplete infarction¹⁷ and white matter damage by altered blood-brain barrier permeability.^11-13Whatever the mechanism, these lesions will be seen on diffusion-weighted imaging (DWI), if at least some of them occur due to an acute process. Given that DWI has a unique contrast property and a relatively short acquisition time, this imaging technique has been incorporated into many routine brain MR protocols, including, among others, protocols for strokes,^18-21 headaches, seizures, and tumors.^22-24Over the past few years, we have used DWI for our routine brain protocol assuming that incidental infarcts would be identified on DWI performed in a general patient population. Although relatively uncommon given the total number of MR examinations that were done, a number of patients with incidental acute or subacute infarcts were identified. These patients'' clinical and imaging data were retrospectively analyzed to elucidate the significance of our observations.     

Characterization of carotid atherosclerosis and detection of soft plaque with use of black-blood MR imaging

BACKGROUND AND PURPOSE: In the treatment of carotid atherosclerosis, the rate of stenosis and characteristics of plaque should be assessed to diagnose vulnerable plaques that increase the risk for cerebral infarction. We performed carotid black-blood (BB) MR imaging to diagnose plaque components and assess plaque hardness based on MR signals.MATERIALS AND METHODS: Three images of BB-MR imaging per plaque were obtained from 70 consecutive patients who underwent carotid endarterectomy (CEA) to generate T1- and T2-weighted images. To evaluate the relative signal intensity (rSI) of plaque components and the relationship between histologic findings and symptoms, we prepared sections at 2-mm intervals from 34 intact plaques. We then calculated the relative overall signal intensity (roSI) of 70 plaques to assess the relationship between MR signal intensity and plaque hardness and symptoms.RESULTS: The characteristics of rSI values on T1- and T2-weighted images of fibrous cap (FC), fibrosis, calcification, myxomatous tissue, lipid core (LC) with intraplaque hemorrhage (IPH), and LC without IPH differed. Symptomatic plaques were associated with FC disruption (P < .001) and LC with IPH (P < .05). The roSI on T1-weighted images was significantly higher for soft than nonsoft plaques. When the roSI cutoff value was set at 1.25 (mean of the roSI), soft plaques were diagnosed with 79.4% sensitivity and 84.4% specificity. The roSI was also significantly higher for symptomatic than for asymptomatic plaques. Soft and nonsoft plaques as well as symptomatic and asymptomatic plaques did not significantly differ on T2-weighted images.CONCLUSION: BB-MR imaging can diagnose plaque components and predict plaque hardness. This procedure provides useful information for planning therapeutic strategies of carotid atherosclerosis.

Carotid atherosclerosis accounts for a large proportion of the causes of cerebral infarction, and accurate diagnostic imaging of carotid stenosis is useful for clarification of the pathogenesis of cerebral infarction and planning of therapy. In the diagnostic imaging of carotid arterial lesions, luminography such as conventional angiography is generally performed to determine the rate of stenosis, and in randomized studies documenting the value of carotid endarterectomy (CEA) in the treatment of carotid atherosclerosis, therapeutic guidelines have been based on stenosis rate.^1–3 Recent studies have also shown the critical importance of diagnosing vulnerable plaques, which are associated with a higher risk for cerebral infarction, by imaging the carotid artery wall itself and determining plaque characteristics.^4,5 Therefore, less invasive and more accurate diagnostic modalities such as carotid ultrasonography (US) for plaque evaluation have considerable importance in the management of patients with carotid atherosclerosis. Carotid US has been widely applied to characterize atherosclerotic plaque, and the content of soft plaque (lipid and hemorrhage) is presently associated with echolucency.^6,7 Furthermore, accumulating evidence indicates that echolucent plaques represent biologically more active disease and are associated with the risk for future stroke.^8,9 In addition, although carotid artery stent placement (CAS) is becoming an increasingly popular alternative to CEA in the treatment of carotid stenosis, several reports have shown that soft plaques are associated with a high incidence of ischemic complication during CAS.^10–12 Therefore, accurate diagnosis of carotid soft plaque seems to be of paramount clinical importance. However, carotid US has some limitations because it is difficult to obtain full images on patients who have a short neck, high carotid bifurcation, or highly calcified plaques.¹³The chemical composition and physical properties of tissues can be determined by MR imaging, which indicates that this diagnostic technique should be useful in plaque characterization. Along with recent advances in imaging devices and techniques, many studies have documented the usefulness of high-resolution MR imaging in the diagnosis of plaque.^14–21 In addition to sorting plaque composition on the basis of MR signal intensity, if soft plaque can be differentiated from nonsoft plaque by overall plaque MR signal intensity, MR imaging will be a simple, objective, and useful method to diagnose carotid atherosclerosis. To our knowledge, however, few studies have closely assessed the MR imaging signals of plaque components by comparing CEA specimens with carotid MR imaging in vivo,²² and the findings on MR imaging of carotid soft plaque have not been described.Our study investigates the benefit of carotid black-blood (BB) MR imaging by evaluating the MR signal intensity of the components of carotid plaque and by detecting soft plaque on the basis of overall plaque MR signal intensity.     

Diagnostic criteria for spontaneous spinal CSF leaks and intracranial hypotension

BACKGROUND AND PURPOSE:Comprehensive diagnostic criteria encompassing the varied clinical and radiographic manifestations of spontaneous intracranial hypotension are not available. Therefore, we propose a new set of diagnostic criteria.MATERIALS AND METHODS: The diagnostic criteria are based on results of brain and spine imaging, clinical manifestations, results of lumbar puncture, and response to epidural blood patching. The diagnostic criteria include criterion A, the demonstration of extrathecal CSF on spinal imaging. If criterion A is not met, criterion B, which is cranial MR imaging findings of spontaneous intracranial hypotension, follows, with at least one of the following: 1) low opening pressure, 2) spinal meningeal diverticulum, or 3) improvement of symptoms after epidural blood patch. If criteria A and B are not met, there is criterion C, the presence of all of the following or at least 2 of the following if typical orthostatic headaches are present: 1) low opening pressure, 2) spinal meningeal diverticulum, and 3) improvement of symptoms after epidural blood patch. These criteria were applied to a group of 107 consecutive patients evaluated for spontaneous spinal CSF leaks and intracranial hypotension.RESULTS: The diagnosis was confirmed in 94 patients, with use of criterion A in 78 patients, criterion B in 11 patients, and criterion C in 5 patients.CONCLUSIONS:A new diagnostic scheme is presented reflecting the wide spectrum of clinical and radiographic manifestations of spontaneous spinal CSF leaks and intracranial hypotension.

Spontaneous intracranial hypotension is an increasingly recognized cause of new daily persistent headaches, particularly among young and middle-aged people, but an initial misdiagnosis remains common.¹ Mechanical factors combine with an underlying structural dural disorder to cause the primary spontaneous spinal CSF leak.^2,3 The prototypical patient with spontaneous intracranial hypotension presents with orthostatic headaches, has pachymeningeal enhancement on cranial MR imaging, and is treated with an epidural blood patch, as reflected by the revised 2004 diagnostic criteria according to the International Classification of Headache Disorders (ICHD-2).⁴ However, it has become well established that the spectrum of clinical as well as radiographic manifestations of spontaneous intracranial hypotension is unusually broad,^1,5 and this is not reflected by the ICHD-2 criteria. We report a new set of diagnostic criteria for spontaneous spinal CSF leaks and spontaneous intracranial hypotension encompassing its varied clinical and radiographic manifestations. The intent of these criteria is to present a diagnostic scheme that can be used to more reliably diagnose spontaneous spinal CSF leaks and intracranial hypotension.     

Comparison of multidetector CT angiography and MR imaging of cervical artery dissection

BACKGROUND AND PURPOSE: Conventional angiography has been historically considered the gold standard for the diagnosis of cervical artery dissection, but MR imaging/MR angiography (MRA) and CT/CT angiography (CTA) are commonly used noninvasive alternatives. The goal of this study was to compare the ability of multidetector CT/CTA and MR imaging/MRA to detect common imaging findings of dissection.MATERIALS AND METHODS: Patients in the data base of our Stroke Center between 2003 and 2007 with dissections who had CT/CTA and MR imaging/MRA on initial work-up were reviewed retrospectively. Two neuroradiologists evaluated the images for associated findings of dissection, including acute ischemic stroke, luminal narrowing, vessel irregularity, wall thickening/hematoma, pseudoaneurysm, and intimal flap. The readers also subjectively rated each vessel on the basis of whether the imaging findings were more clearly displayed with CT/CTA or MR imaging/MRA or were equally apparent.RESULTS: Eighteen patients with 25 dissected vessels (15 internal carotid arteries [ICA] and 10 vertebral arteries [VA]) met the inclusion criteria. CT/CTA identified more intimal flaps, pseudoaneurysms, and high-grade stenoses than MR imaging/MRA. CT/CTA was preferred for diagnosis in 13 vessels (5 ICA, 8 VA), whereas MR imaging/MRA was preferred in 1 vessel (ICA). The 2 techniques were deemed equal in the remaining 11 vessels (9 ICA, 2 VA). A significant preference for CT/CTA was noted for VA dissections (P < .05), but not for ICA dissections.CONCLUSION: Multidetector CT/CTA visualized more features of cervical artery dissection than MR imaging/MRA. CT/CTA was subjectively favored for vertebral dissection, whereas there was no technique preference for ICA dissection. In many cases, MR imaging/MRA provided complementary or confirmatory information, particularly given its better depiction of ischemic complications.

Dissection of the extracranial arteries accounts for 10%–25% of strokes in young and middle-aged patients.¹ It may be spontaneous or traumatic and can cause a variety of clinical presentations, including stroke, headache, neck pain, tinnitus, Horner syndrome, and cranial neuropathies.^1-4 Dissections are typically diagnosed on the basis of a combination of the clinical presentation, imaging studies (conventional angiography, CT/CT angiography [CTA], MR imaging/MR angiography [MRA], and sonography), and exclusion of other arterial disease, particularly atherosclerosis.^1,2,5 In patients with mild or atypical symptoms, noninvasive imaging may facilitate earlier diagnosis and prevent embolic ischemic complications with the use of antithrombotic therapy.^3,6Conventional angiography has historically been considered the gold standard for dissection diagnosis, but it has limitations, which include its cost and invasiveness.^1,7,8 Although the angiographic appearance of dissection is often characteristic, it does not assess the vessel wall for intramural hematoma; because of this feature, dissections in unusual locations or with atypical morphology may be misclassified or attributed to other processes. MR imaging/MRA and CT/CTA have emerged as viable alternatives for both diagnosis and follow-up of dissection.^9-15 In general, the 2 techniques have different strengths and weaknesses. Diffusion-weighted MR imaging is a powerful technique for detecting acute stroke,¹⁶ which may then lead to increased scrutiny of the upstream arterial tree. Axial T1-weighted fat-suppressed images can detect the methemoglobin of the intramural hematoma within the false lumen, a finding referred to as a crescent sign.^9,13 Multidetector CT/CTA has enabled routine acquisition of thinner sections with rapid imaging times, facilitating multiplanar and volume reconstructions. Additionally, it is more widely available (especially at night), has fewer contraindications, and provides greater spatial resolution than MR imaging/MRA. However, the use of ionizing radiation in the relatively young population of patients with dissection is potentially concerning, especially given the often frequent follow-up studies in these patients.Only 1 study to date has compared CT/CTA with MR imaging/MRA for evaluation of dissection, retrospectively reviewing 7 internal carotid dissections and showing CTA to be marginally more effective in the identification of the dissected vessel.¹¹ To our knowledge, this current study is the largest comparative series of cervical artery dissection imaged with both tomographic techniques. Given the higher spatial resolution of CT/CTA, we hypothesized that CT/CTA may be particularly suited to visualize dissections within the smaller vertebral arteries. Additionally, we hypothesized that in a series of known dissections, CT/CTA would be more sensitive to identify specific imaging features associated with dissections.     

High b-value diffusion tensor imaging of the neonatal brain at 3T

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging studies of the adult brain have shown that contrast between lesions and normal tissue is increased at high b-values. We designed a prospective study to test the hypothesis that diffusion tensor imaging (DTI) obtained at high b-values increases image contrast and lesion conspicuity in the neonatal brain.MATERIALS AND METHODS: We studied 17 neonates, median (range) age of 10 (2–96) days, who were undergoing MR imaging for clinical indications. DTI was performed on a Philips 3T Intera system with b-values of 350, 700, 1500, and 3000 s/mm². Image contrast and lesion conspicuity at each b-value were visually assessed. In addition, regions of interest were positioned in the central white matter at the level of the centrum semiovale, frontal and occipital white matter, splenium of the corpus callosum, posterior limb of the internal capsule, and the thalamus. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values for these regions were calculated.RESULTS: Isotropic diffusion image contrast and lesion-to-normal-tissue contrast increased with increasing b-value. ADC values decreased with increasing b-value in all regions studied; however, there was no change in FA with increasing b-value.CONCLUSIONS: Diffusion image contrast increased at high b-values may be useful in identifying lesions in the neonatal brain.

Diffusion-weighted MR imaging is increasingly being used to investigate neonatal cerebral pathologic lesions. Previous studies have shown that diffusion-weighted imaging (DWI) is able to demonstrate lesions that are not always discernible on conventional MR imaging, and the usefulness of this imaging technique to assess infarction^1-3 and metabolic disorders^4,5 in the neonatal brain is established. In addition to the qualitative assessment of injury, diffusion tensor imaging (DTI) provides directionally invariant measurements of mean diffusivity and diffusion anisotropy. These objective measurements provide information regarding water molecular mobility, which reflect tissue microstructure and thereby provide insight into mechanisms of brain development and disease processes.Diffusion-weighted MR imaging with b-values of more than 2000 s/mm² has been performed in animal studies,^6,7 in the adult brain,^8-14 and in infants.^8,15 These studies suggest that diffusion contrast characteristics are altered at higher b-values. In addition, adult studies of cerebral infarction¹³ and white matter disease¹⁴ have shown increased lesion conspicuity at higher b-values, and so it is possible that high b-value DTI in neonates may also improve lesion conspicuity.To our knowledge, the only studies investigating the effects of high b-value diffusion imaging in the neonatal brain were done on infants whose results on conventional MR imaging was considered normal and did not examine the full diffusion tensor.^8,15 In this prospective study, we tested the hypothesis that diffusion imaging at high b-values enhances contrast between lesions and normal tissue in neonates and thereby increases lesion conspicuity. Furthermore, we acquired diffusion data in 6 noncollinear directions of sensitization, enabling us to examine the effects of high b-values on diffusion anisotropy.The aims of this study were 1) to assess isotropic DWI contrast and lesion conspicuity at b-values between 350 and 3000s/mm² and 2) to assess whether apparent diffusion coefficient (ADC) or fractional anisotropy (FA) in the neonatal brain change with increasing b-value.