Diffusion- and perfusion-weighted MR imaging of dural sinus thrombosis

A patient with dural sinus thrombosis had progressively worsening symptoms and signs that resolved after intradural thrombolysis. Intradural sinus pressures were 54 mm Hg. Echo-planar MR imaging revealed complex abnormalities of diffusion and widespread delay in mean transit time that improved immediately after thrombolysis. This case suggests that diffusion- and perfusion-weighted imaging can provide valuable information noninvasively to help triage patients with dural sinus thrombosis between conservative and aggressive management.     

Parenchymal abnormalities associated with cerebral venous sinus thrombosis: assessment with diffusion-weighted MR imaging

BACKGROUND AND PURPOSE: The common entity cerebral venous sinus thrombosis is associated with the poorly characterized imaging finding of parenchymal abnormalities; diffusion-weighted imaging has offered some insight into these manifestations. We assessed the relationship between the diffusion constant from apparent diffusion coefficient (ADC) maps in patients with cerebral venous thrombosis (CVT) with follow-up imaging findings and clinical outcome. METHODS: We evaluated the medical records and T2-weighted MR images of 13 patients with CVT complicated by intraparenchymal abnormality. Diffusion-weighted (DW) images and ADC maps were evaluated for increased, decreased, or unchanged signal intensity and were compared with signal intensity of contralateral, normal-appearing brain. In addition, ADCs were obtained in nine pixel regions of interest in abnormal regions in eight of the 13 patients. RESULTS: Eight patients had superficial CVT, and five had superficial and deep CVT. CVT of deep veins was associated with deep gray nucleus and deep white matter abnormalities, whereas superficial CVT was associated with cortical and subcortical abnormalities. Twenty-four nonhemorrhagic lesions were identified in 10 of 13 patients on the basis of follow-up imaging findings. Four patients without seizures had lesions with decreased diffusion that appeared hyperintense on follow-up T2-weighted images, three patients with seizures had lesions with decreased diffusion that resolved, and seven patients had lesions with increased diffusion that resolved. Three of 10 patients had more than one lesion type. No difference was noted in mean ADCs for lesions with decreased diffusion that resolved compared with lesions with decreased diffusion that persisted. CONCLUSION: DW imaging in these patients disclosed three lesion types: lesions with elevated diffusion that resolved, consistent with vasogenic edema; lesions with low diffusion that persisted, consistent with cytotoxic edema in patients without seizure activity; and lesions with low diffusion that resolved in patients with seizure activity. This information may be important in prospectively determining severity of irreversible injury and in patient treatment.     

Magnetic resonance imaging of carotid artery abnormalities in patients with sphenoid sinusitis

Sphenoid sinusitis is unusual in children, but when it occurs, it can lead to serious intracranial complications. We show the value of MRI in demonstrating intracranial abnormalities due to sphenoid sinus infection, particularly those involving the internal carotid arteries and cavernous sinuses. We reviewed our imaging experience of sphenoid sinusitis and found four patients with ICA narrowing who had undergone MR evaluation including conventional and diffusion imaging. MR angiography was also performed in three patients to determine the extent of ICA narrowing. Narrowing of ICA was found in the cavernous segment in all patients and in the supraclinoid segment in three. Cerebral infarction was found in two patients. In one patient the cavernous sinus showed hyperintensity on diffusion-weighted images and hypointensity on apparent diffusion coefficient map, suggesting reduced diffusion. Although infrequent in children, sphenoid sinus infection should be considered as a possible cause of intracranial infection, particularly in teenagers. Early recognition of cavernous sinus involvement and ICA narrowing may lead to prompt treatment and hence a more favorable outcome.     

Neurotoxicity of intrathecal methotrexate: MR imaging findings

We report a case of intrathecal methotrexate neurotoxicity manifesting as left arm weakness and aphasia. Diagnostic imaging showed restricted diffusion and fluid-attenuated inversion recovery imaging findings were normal at presentation. Three weeks later, diffusion abnormalities resolved, and T2-weighted studies showed increased signal intensity of prolonged T2 changes in areas of prior restricted diffusion. We attribute the clinical and radiographic findings to cytotoxic edema secondary to intrathecal methotrexate.     

Restricted diffusion in bilateral optic nerves and retinas as an indicator of venous ischemia caused by cavernous sinus thrombophlebitis

A 44-year-old man developed bilateral blindness following severe periorbital cellulitis and pansinusitis. CT and MR imaging demonstrated bilateral cavernous sinus thrombosis. Diffusion-weighted imaging revealed reduced apparent diffusion coefficient in bilateral optic nerves, suggesting optic nerve ischemia caused by the cavernous sinus thrombophlebitis (CST). Following surgical debridement of pansinusitis, antimicrobial therapy, and anticoagulation, the patient recovered from the infectious episode but sustained permanent bilateral blindness. This case shows that both retinal and optic nerve ischemia can be the cause of blindness after CST. Arguments supporting an arterial-versus-venous origin for the ischemia are discussed.     

Q-ball imaging.

Magnetic resonance diffusion tensor imaging (DTI) provides a powerful tool for mapping neural histoarchitecture in vivo. However, DTI can only resolve a single fiber orientation within each imaging voxel due to the constraints of the tensor model. For example, DTI cannot resolve fibers crossing, bending, or twisting within an individual voxel. Intravoxel fiber crossing can be resolved using q-space diffusion imaging, but q-space imaging requires large pulsed field gradients and time-intensive sampling. It is also possible to resolve intravoxel fiber crossing using mixture model decomposition of the high angular resolution diffusion imaging (HARDI) signal, but mixture modeling requires a model of the underlying diffusion process.Recently, it has been shown that the HARDI signal can be reconstructed model-independently using a spherical tomographic inversion called the Funk-Radon transform, also known as the spherical Radon transform. The resulting imaging method, termed q-ball imaging, can resolve multiple intravoxel fiber orientations and does not require any assumptions on the diffusion process such as Gaussianity or multi-Gaussianity. The present paper reviews the theory of q-ball imaging and describes a simple linear matrix formulation for the q-ball reconstruction based on spherical radial basis function interpolation. Open aspects of the q-ball reconstruction algorithm are discussed.     

Brain stem hypertensive encephalopathy evaluated by line scan diffusion-weighted imaging

Hypertensive encephalopathy rarely presents with predominant involvement of the brain stem and relative sparing of the supratentorial regions. We describe the MR imaging features in a patient with reversible brain stem hypertensive encephalopathy. Extensive hyperintensity was predominantly seen in brain stem regions on fluid-attenuated inversion-recovery and T2-weighted images. These lesions showed an increased apparent diffusion coefficient with the use of line scan diffusion-weighted imaging. The clinical findings and MR imaging abnormalities resolved with control of hypertension.     

A regularized two-tensor model fit to low angular resolution diffusion images using basis directions

PURPOSE: To resolve and regularize orientation estimates for two crossing fibers from images acquired with conventional diffusion tensor imaging (DTI) sampling schemes. MATERIALS AND METHODS: Partial volume causes artifacts in DTI. Given that routine use of high angular resolution diffusion imaging (HARDI) is still tentative, a regularized two-tensor model to resolve fiber crossings from conventional DTI datasets is presented. To overcome the problems of fitting multiple tensors, a model that exploits the planar diffusion profile in regions with fiber crossings is utilized. A regularization scheme is applied to reduce noise artifacts, which can be significant due to the relatively low number of acquired images. A set of basis directions is used to convert the two tensor model to many models of lower dimensionality. Relaxation labeling is utilized to select from amongst these models those that preserve continuity of orientations across neighbors. Revised fractional anisotropy (FA) and mean diffusivity (MD) values are computed. RESULTS: Spatial regularization improves the orientation estimates of the two-tensor model in simulations and in human data and estimates agree well with a priori anatomical knowledge. CONCLUSION: Orientational, anisotropy, and diffusivity information can be resolved in regions of two fiber crossings using full brain coverage scans acquired in less than six minutes.     

Diffusion and perfusion MR imaging in stroke

Magnetic resonance imaging (MRI) in stroke makes it possible to visualize the initial infarct in cases of acute cerebral ischemia. Perfusion MRI serves to determine which tissues are additionally at risk of infarction due to persistent hypoperfusion. MRI also allows those examiners with limited experience to reliably confirm an infarct. The most important differential diagnosis of cerebral ischemia, intracerebral hemorrhage, can likewise be recognized with certainty using MRI. Although diffusion and perfusion MRI only demonstrate the pathophysiology of cerebral ischemia approximately, the method is suited for identifying those patients who would profit from reperfusion therapy. Whether MRI is also appropriate as an aid to reaching a prognosis on the risk of secondary hemorrhage has not yet been resolved.     

Extracerebral cavernous hemangioma of the cavernous sinus: diagnosis with MR imaging and labeled red cell blood pool scintigraphy

We present the case of a 64-year-old man with a presumed diagnosis of extracerebral cavernous hemangioma involving the cavernous sinus. The diagnosis was made on the basis of labeled red cell blood pool scintigraphy findings in conjunction with those of MR imaging. This lesion was not altered in appearance at 6-year follow-up MR imaging. We also present the labeled red cell blood pool scintigraphy findings obtained in three other patients with similar-appearing cavernous sinus lesions at MR imaging who underwent subsequent biopsy; histologic findings confirmed chondrosarcoma, chordoma, and meningioma, respectively.     

Echo planar diffusion tensor imaging of the mouse spinal cord at thoracic and lumbar levels: A feasibility study

Diffusion tensor imaging is increasingly used for probing spinal cord (SC) pathologies, especially in mouse models of human diseases. However, diffusion tensor imaging series requires a long acquisition time and mouse experiments rarely use rapid imaging techniques such as echo planar imaging. A recent preliminary study demonstrated the feasibility and robustness of the echo planar imaging sequence for mouse cervical SC diffusion tensor imaging investigations. The feasibility of echo planar imaging at thoracic and lumbar levels, however, remained unknown due to bulk motion, field inhomogeneities, and off‐centering of the SC in the axial plane. In the present study, the feasibility and the robustness of an echo planar imaging–based diffusion tensor imaging sequence for mouse thoracic and lumbar SC investigations is demonstrated. Quantitative and accurate diffusion tensor imaging metrics, as well as high spatially resolved images, have been obtained. This successful demonstration may open new perspectives in the field of mouse SC imaging. Echo planar imaging is used in several imaging modalities, such as relaxometry or perfusion, and may prove to be very attractive for multimodal MR investigations to acquire a more detailed characterization of the SC tissue. Magn Reson Med 63:1125–1134, 2010. © 2010 Wiley‐Liss, Inc.     

Central tegmental tract involvement in an infant with 6-pyruvoyltetrahydropterin synthetase deficiency

We report the case of an asymptomatic 2-month-old infant with 6-pyruvoyltetrahydropterin synthetase deficiency detected through a neonatal phenylketonuria screening program. MR imaging revealed symmetrical lesions in the central tegmental tract with reduced diffusion, which resolved after treatment. A possible explanation for these lesions is intramyelinic edema resulting from brain insults in utero.     

Serial investigation of perfusion disturbances and vasogenic oedema in hypertensive encephalopathy by diffusion and perfusion weighted imaging

Serial MRI including diffusion and perfusion imaging was performed in a patient with hypertensive encephalopathy. At admission, the patient was disorientated and presented with seizures and cortical blindness. Perfusion imaging showed a marked reduction in blood volume and flow, with corresponding vasogenic oedema in the occipital, posterior temporal, and, to a lesser extent, frontal lobes. The clinical symptoms disappeared rapidly following treatment, whereas the disturbed circulation pattern and vasogenic oedema resolved more slowly. A complete normalisation was seen after 1 year.     

Pilonidal sinus disease: MR imaging distinction from fistula in ano

PURPOSE: To describe magnetic resonance (MR) imaging features in patients with proved pilonidal sinus disease and to compare these features with those in a matched group of patients with proved fistula in ano to determine the accuracy with which MR imaging can be used to distinguish between the two diseases. MATERIALS AND METHODS: Seven patients with pilonidal sinus disease underwent MR imaging with a body coil. The site and morphology of sepsis were noted, with particular reference to natal cleft sepsis and deep-seated sepsis, including intersphincteric anal canal sepsis and any enteric communication. Comparison was made with 14 age- and sex-matched patients with fistula in ano. Categoric frequencies were compared to calculate differences between the groups and sensitivities, specificities, and predictive values. RESULTS: All patients with pilonidal sinus had natal cleft sepsis, but five (71%) had sepsis at deep-seated sites more characteristic of fistula in ano. Eight patients with fistula in ano (57%) had natal cleft sepsis that was thought characteristic of pilonidal sinus. No patient with pilonidal sinus had intersphincteric sepsis or an enteric communication, in contrast to all patients with fistula in ano having both (P <.001). Natal cleft sepsis reached the subcutaneous tissues overlying the coccyx and sacrum in only one patient with fistula (7%), in contrast to six (86%) with pilonidal sinus (P <.001). MR imaging had a sensitivity of 86% (six of seven), specificity of 100% (14 of 14), positive predictive value of 100% (six of six), and negative predictive value of 93% (14 of 15) for diagnosis of pilonidal sinus disease. CONCLUSION: MR imaging features of perianal and deep-seated sepsis, characteristic of fistula in ano, are also found in patients with pilonidal sinus, but the absence of intersphincteric sepsis or enteric opening allows reliable MR imaging distinction between the two.     

Hypertensive encephalopathy of brain stem with minimal supratentorial involvement: a rare manifestation of hypertensive encephalopathy

We report a case of a 38-year-old man with brain stem hypertensive encephalopathy. MR imaging revealed diffuse hyperintensities in the brain stem. Diffusion-weighted imaging (DWI) was normal, and apparent diffusion coefficient (ADC) values were increased in the brain stem. The supratentorial regions were largely spared, and only subtle high intensities were seen. The lesions completely resolved after stabilization of blood pressure. The findings of normal DWI and high ADC values were compatible with vasogenic edema due to hypertension.     

Diffusion tensor imaging in an infant with traumatic brain swelling

We present the case of a 14-month-old male infant who underwent diffusion tensor imaging within 24 hours of traumatic brain injury. Although conventional MR findings that included those of diffusion-weighted imaging were unremarkable, full-tensor diffusion imaging revealed striking abnormalities in regions of brain that subsequently developed overt swelling. This case engenders important hypotheses regarding mechanisms of traumatic brain swelling and anisotropic diffusion of water in pathologic tissues.     

MRI appearances of the sphenoid sinus at the late follow-up of trans-sphenoidal surgery for pituitary macroadenoma

We aimed to demonstrate the appearances of the sphenoid sinus on MRI performed later than 2 years post- transsphenoidal surgery (TSS). We retrospectively reviewed 47 patients in whom follow-up MRI scans had been performed at least 2 years post-TSS. We specifically reviewed the clinical and imaging of those patients in whom the sphenoid sinus was filled with signal abnormality or masses were present arising from the sinus roof and classified them as tumour or indeterminate abnormalities on imaging criteria. We documented other clinicoradiological details. Twelve of 47 patients demonstrated sphenoid sinus filling or sinus roof masses and in six of 12 patients it was possible to classify them as tumourous using imaging and clinical criteria. The indeterminate and non-tumourous sphenoid sinus abnormalities most frequently had a T1-weighted signal similar to subsellar tumour and displayed rim enhancement and thus could not be reliably distinguished from tumourous abnormality on the basis of signal or enhancement characteristics. The presence of a well-defined surgical defect in the sella floor was associated with resolution of abnormality on MRI follow-up. We concluded MRI findings of sphenoid sinus filling or sinus roof masses are present in approximately 26% of scans performed longer than 2 years post-TSS. Half of these are of indeterminate origin and follow-up is required to discriminate tumour from non- tumour with certainty. A well-defined surgical defect in the sella floor is, however, suggestive of a non-tumourous abnormality.     

Band-like hyperintensity along the ventral surface of the brain stem on FLAIR and DWI in leptomeningeal carcinomatosis of lung adenocarcinoma

Since leptomeningeal carcinomatosis is rarely observed before diagnosis of the primary cancer, its detection is often delayed. We report the case of a 60-year-old woman who presented with lung adenocarcinoma with leptomeningeal carcinomatosis. Magnetic resonance imaging showed the characteristic abnormal hyperintensity along the ventral surface of the brain stem on fluid-attenuated inversion recovery and diffusion weighted imaging. It had no contrast uptake. Based on these findings, we were able to make an early diagnosis of leptomeningeal carcinomatosis of lung adenocarcinoma. This condition was resolved after treatment with a tyrosine kinase inhibitor.     

Para-cavernous sinus venous structures: anatomic variations and pathologic conditions evaluated on fat-suppressed 3D fast gradient-echo MR images

BACKGROUND: The cavernous sinus communicates with several para-cavernous sinus venous structures, receiving blood flow from the superficial middle cerebral vein (SMCV), the sphenoparietal sinus (SPS), and the superior ophthalmic vein, and draining into the superior and inferior petrosal sinuses and pterygoid and basilar plexuses. Anatomic variations of these veins have been previously reported; however, some details, such as the relationship between the SPS and the SMCV, are incompletely characterized. The anatomic variations of para-cavernous sinus veins, especially drainage patterns of the SMCV, were evaluated on MR imaging. MATERIALS AND METHODS: Thirty-seven patients, including those without any lesions affecting the cavernous sinus or para-cavernous veins and patients with carotid cavernous fistulas, were examined by using fat-suppressed contrast-enhanced 3D fast gradient-echo MR imaging. Two neuroradiologists evaluated the images on a viewer, regarding the normal anatomy and the pathologic findings of the para-cavernous sinus veins. RESULTS: The fat-suppressed 3D fast gradient-echo MR images clearly depicted the para-cavernous sinus venous structures in all patients. SMCVs had 4 variations in the drainage patterns. The most frequent pattern was drainage into the SPS (39%), and other types were draining into cavernous sinus, pterygoid plexus, and tentorial sinus. The SPS had 3 variations. The most frequent pattern was drainage into cavernous sinus (72%), and others were the hypoplastic type or those draining into pterygoid plexus. CONCLUSION: The fat-suppressed 3D fast gradient-echo MR image is useful for evaluating the venous structures in the skull base. Knowledge of the variations is important for diagnosis and endovascular treatment of the cavernous sinus lesions.     

High angular resolution diffusion imaging reveals intravoxel white matter fiber heterogeneity.

Magnetic resonance (MR) diffusion tensor imaging (DTI) can resolve the white matter fiber orientation within a voxel provided that the fibers are strongly aligned. However, a given voxel may contain a distribution of fiber orientations due to, for example, intravoxel fiber crossing. The present study sought to test whether a geodesic, high b-value diffusion gradient sampling scheme could resolve multiple fiber orientations within a single voxel. In regions of fiber crossing the diffusion signal exhibited multiple local maxima/minima as a function of diffusion gradient orientation, indicating the presence of multiple intravoxel fiber orientations. The multimodality of the observed diffusion signal precluded the standard tensor reconstruction, so instead the diffusion signal was modeled as arising from a discrete mixture of Gaussian diffusion processes in slow exchange, and the underlying mixture of tensors was solved for using a gradient descent scheme. The multitensor reconstruction resolved multiple intravoxel fiber populations corresponding to known fiber anatomy. Ma