MR imaging of extracranial hematomas: comparison with CT

Thirty MR examinations of twenty-five patients with extracranial hemorrhagic lesions were reviewed. Comparative CT studies were available in 11 patients. The acute hematomas (less than 3 days old) showed intermediate intensity on the short TR (0.5 sec.) and increased in signal intensity on the long TR (2.0 sec.). The MR appearance of acute hematoma was not specific. Clot (more than 3 days old) demonstrated an intermediate intensity on the short TR and increased markedly in signal intensity on the long TR equaling the signal intensity of fat. Serum (more than 3 days old) was imaged as a high intensity lesion on both short and long TR. It is concluded that MR can be very useful for the differential diagnosis of subacute and chronic hemorrhagic lesions from other lesions.     

Intracranial hematomas: imaging by high-field MR

Twenty intracranial hematomas between 1 day and over 1 year old were imaged using magnetic resonance at 1.5 T, with T1- and T2-weighted spin-echo pulse sequences. Characteristic intensity patterns were observed in the evolution of the hematomas, which could be staged as acute (less than 1 week old), subacute (greater than 1 week and less than 1 month old), or chronic (greater than 1 month old). Acute hematomas were characterized by central hypointensity on T2-weighted images (WIs). Subacute hematomas had peripheral hyperintensity on T1-WIs and then on T2-WIs. This hyperintensity proceeded to fill in the hematoma in the chronic stage. In subacute and chronic hematomas, there was hypointensity on T2-WIs in the immediately adjacent part of the brain. On T2-WIs of acute and subacute hematomas, the nearby white matter was characterized by hyperintensity, consistent with edema. A different mechanism is proposed for each of the three characteristic intensity patterns. Two of these mechanisms increase in proportion to the square of the magnetic field magnitude.     

MR imaging of extracranial nerve sheath tumors.

We retrospectively reviewed MR images of 32 histologically proven extracranial nerve sheath tumors (NSTs). There were 23 benign (10 neurofibromas, 13 schwannomas) and 9 malignant NSTs. On T1-weighted images (T1WIs) tumors were isointense or slightly hyperintense to muscle. On T2-weighted images (T2WIs) (11 lesions) and enhanced T1WIs (1 intraspinal lesion), a target pattern with peripheral hyperintense rim and central low intensity was seen in 12 of 23 (52%) benign NSTs (5 of 10 neurofibromas and 7 of 13 schwannomas). This pattern corresponded histologically to peripheral myxomatous tissue and central fibrocollagenous tissue. The pattern was absent in lesions with cystic, hemorrhagic, or necrotic degeneration. These tumors were hyperintense and variably inhomogenous on T2WIs. Malignant NSTs were hyperintense and variably inhomogenous on T2WIs and mimicked benign variably inhomogeneous lesions unless involvement of contiguous structures was visualized. A target pattern was not visible in malignant lesions. Magnetic resonance imaging cannot distinguish schwannomas from neurofibromas, and benign tumors may mimic malignant NSTs when cystic, hemorrhagic, and necrotic degeneration is present. A target pattern may be visualized in some benign NSTs, and evaluation of this sign with assessment of location and growth along nerves may help to avoid confusion with other lesions.     

High-field, high-resolution MR imaging of the human indusium griseum

The human indusium griseum (IG), the paired dorsal continuation of the hippocampus, was investigated with high-field (3.0T) MR imaging. The IG was clearly visible in 16 out of 20 healthy volunteers. The most common pattern was a single lateralized strip. The classical neuroanatomic pattern of paired symmetric strips along the midline was found in one case. The study clearly demonstrates that diminutive, hitherto overlooked structures such as the IG now can be readily investigated in vivo by non-invasive high-field MR imaging.     

High-field MR imaging of superficial siderosis of the central nervous system

A case of superficial siderosis of the central nervous system secondary to bleeding from an ependymoma is presented. High-field magnetic resonance imaging showed marginal hypointensity of the cervical cord, medulla oblongata, pons, mesencephalon, anterior cerebellar and basal cerebral surfaces, and cranial nerves (II, V, VIII). These findings were evident in the T2 weighted images.     

MR imaging in the diagnosis of spontaneous spinal epidural hematomas

Three patients with spontaneous (idiopathic) spinal epidural hematomas were diagnosed with magnetic resonance (MR) imaging. Magnetic resonance is an accurate, rapid method of localizing and characterizing the hematomas. We believe that MR (where available) should be the primary method of diagnosis in cases in which spinal epidural hematoma is suspected.     

The biophysical basis of tissue contrast in extracranial MR imaging

So that radiologists can understand better the differences between tissues that determine MR image contrast, the biophysical basis of proton-MR tissue contrast is reviewed. Differences in the molecular sizes of water, fat, and protein macromolecules affect the rate of molecular motion, which in turn influences relaxation times. Differences in the physical state of water within tissues determine the extent to which the motion of water is restricted by binding to hydrophilic macromolecules (e.g., protein), which in turn causes variable amounts of T1 and T2 shortening. Understanding these concepts and knowing the location in the body of free water, cellular tissues, fat, collagen, bone, and tissue iron improve the radiologist's ability to extract useful information from MR images.     

Intracranial hematomas studied by MR imaging at 0.17 and 0.02 T

The contrast in magnetic resonance (MR) images relies mainly on the relaxation time differences between the tissues. The relative differences in relaxation times T1 are bigger at lower field strengths, although the absolute values of T1 are smaller. A shorter T1 is also advantageous for the contrast of the T2 and proton density weighted images because of the more complete recovery of the spin system during the repetition time TR. Scrutiny of the clinical results of MR shows some unsolved problems in the specificity of diagnosing fresh intracranial hematomas. Low field MR imaging at 0.02 T seems to offer new vistas in this sense. Fresh subdural hematoma was more easily detected and differentiated at 0.02 T than at 0.17 T. The T2 of fresh intracranial hematomas was rather short compared with cerebrospinal fluid and edema and, unlike T1, was not highly dependent on magnetic field strength. The different visualization of acute versus late intracerebral hematoma and the changes during the resorption were demonstrated in follow-up studies of two patients at 0.17 T and of one at 0.02 T. In one patient the same lesion was imaged successively at both field strengths, showing the divergent contrast in the inversion recovery images at 0.02 and 0.17 T.     

High-field spin-echo MR imaging of superficial and subependymal siderosis secondary to neonatal intraventricular hemorrhage

Summary Two cases of superficial siderosis with subependymal siderosis, secondary to neonatal intraventricular hemorrhage, are presented. High-field spin-echo MR imaging (1.5 Tesla) showed marginal hypointensity of the ventricular walls as well as of the subpial regions. These findings were most evident on T₂ weighted images, characteristic of hemosiderotic deposits.     

High-field MR findings of multiple system atrophy

Magnetic resonance images obtained at 1.5T were reviewed in 23 patients with clinically diagnosed multiple system atrophy (MSA). The patient group consisted of 13 cases with olivoponto-cerebellar atrophy (OPCA), three with striatonigral degeneration (SND), and seven with Shy-Drager syndrome (SDS). In each disorder group, hypointensity of the pars compacta of the substantia nigra was frequently demonstrated as well as the atrophy of the brain stem and cerebellum. Although T2-weighted images depicted hypointensity of the putamen, which was prominent in its posterolateral part, in cases with SND and SDS, it was not encountered in cases with OPCA. Therefore, this finding was considered to facilitate differential diagnosis between OPCA and other two disorders. These hypointensities in the putamen and pars compacta of the substantia nigra may be due to excessive iron deposition and seem to correlate with extrapyramidal tract signs of MSA.     

High-field and low-field MR imaging of superior glenoid labral tears and associated tendon injuries

OBJECTIVE: The purpose of this study was to determine the performance characteristics of high-field and low-field MR imaging for the diagnosis of a glenoid superior labral anteroposterior (SLAP) tear. MATERIALS AND METHODS: High-field (n = 46) or low-field (n = 21) MR imaging was performed on 41 patients with SLAP tears and 26 patients with normal superior labra. The superior labrum was classified into one of four types on the basis of patterns of intralabral signal intensity. The relative frequency of rotator cuff tears and long head of the biceps tendinopathy was also assessed. RESULTS: For the diagnosis of SLAP tear, the sensitivity of high-field MR imaging was 90% (95% confidence interval = 74%, 98%), specificity was 63% (35%, 85%), and accuracy was 80% (66%, 91%). The sensitivity of low-field MR imaging was 64% (31%, 89%), specificity was 70% (35%, 93%), and accuracy was 67% (43%, 85%). A branched linear or stellate focus of abnormal intralabral signal intensity was associated with a SLAP tear in 86% of patients. Conversely, two other labral patterns correlated with a normal superior labrum in 71% of patients. Abnormal signal intensity in the biceps tendon was seen in 15% of patients with a SLAP tear. Full-thickness (37%) and partial-thickness (31%) rotator cuff tears were often seen. CONCLUSION: The performance characteristics of high-field MR imaging are superior to those of low-field MR imaging for the diagnosis of a superior labral tear. Rotator cuff tears can be seen in many patients with superior labral tears, but abnormal signal intensity in the biceps tendon is uncommon.     

Diffusion measurements in intracranial hematomas: implications for MR imaging of acute stroke

BACKGROUND AND PURPOSE: The purpose of our study was to analyze the diffusion properties of intracranial hematomas to understand the effects of hematomas on diffusion-weighted MR images of patients with acute stroke and to further our understanding of the evolution of signal intensities of hematomas on conventional MR images. We hypothesized that hematomas containing blood with intact RBC membranes (ie, early hematomas) have restricted diffusion compared with hematomas in which RBC membranes have lysed. METHODS: Seventeen proven intracranial hematomas were studied with conventional and diffusion MR imaging. Hematomas were characterized using conventional images to determine the stage of evolution and their putative biophysical composition, as described in the literature. Apparent diffusion coefficient (ADC) measurements for each putative hematoma constituent (intracellular oxyhemoglobin, intracellular deoxyhemoglobin, intracellular methemoglobin, and extracellular methemoglobin) were compared with each other and with normal white matter. RESULTS: Hematomas showing hemoglobin within intact RBCs by conventional MR criteria (n = 14) showed equivalent ADC values, which were reduced compared with hematomas containing lysed RBCs (P = .0029 to .024). Compared with white matter, hematomas containing lysed RBCs had higher ADC measurements (P = .003), whereas hematomas containing intact RBCs had reduced ADC measurements (P < .0001). CONCLUSION: Restricted diffusion is present in early intracranial hematomas in comparison with both late hematomas and normal white matter. Therefore, early hematomas would be displayed as identical to the signal intensity of acute infarction on ADC maps, despite obvious differences on conventional MR images. These data also are consistent with the biochemical composition that has been theorized in the stages of evolving intracranial hematomas and provide further evidence that paramagnetic effects, rather than restriction of water movement, are the dominant cause for their different intensity patterns on conventional MR images.     

MR imaging of cerebral hematomas at different field strengths: theory and applications

Existing theory on relaxation effects in blood and their field dependence is related to magnetic resonance (MR) imaging of hematomas. These effects include (a) relaxation caused by protein and other macromolecules; (b) inhomogeneous susceptibility created by paramagnetic forms of hemoglobin (Hb) (deoxy and met) within the red blood cells; and (c) direct interaction of water protons with paramagnetic metHb. The effect of proton density is also discussed. These effects combine in a complex way to create hypo- or hyper-intensity on MR images of hematomas. Further, the effects change as the hematoma evolves both physically and chemically. In particular, there are five stages that are associated with typical image appearance: (a) oxygenated blood; (b) deoxygenated blood; (c) conversion to metHb; (d) hemolysis; and (e) protein resorption.     

High-field MR surface-coil imaging of the hand and wrist. Part I. Normal anatomy

High-resolution magnetic resonance (MR) images of the hands and wrists of six healthy volunteers were obtained at 1.5 T with a surface coil. Additionally, the hands and wrists of two fresh cadavers were imaged and were subsequently sectioned for anatomic correlation. High contrast when depicting soft-tissue, coupled with impressive spatial resolution and multiplanar capabilities, enabled delineation of fine structures including nerves, tendons, and blood vessels. Osseous and cartilaginous structures were also well depicted. MR imaging gives anatomic definition of the hand and wrist unmatched by other diagnostic imaging methods.     

MR findings in extracranial cysticercosis

A patient with disseminated cysticercosis involving orbit, tongue, parotid glands, epicardial fat, muscle, and subcutaneous tissues is presented. Magnetic resonance findings are described with emphasis on intraorbital and extracranial lesions.     

Pediatric extracranial applications of MR angiography

Extracranial magnetic resonance angiography (MRA) was performed in 20 children to evaluate for various arterial and venous conditions. Time-of-flight and phase-contrast angiograms were constructed using a maximal-intensity-projection algorithm. The accuracy of MRA was comparable to Doppler ultrasound (n = 12) and conventional angiography (n = 3). MRA could provide an excellent mapping of patent (including collaterals) versus thrombosed vessels at sites not evaluated or inaccessible by sonography. Limitations included assessment of small and/or tortuous vessels, severely stenotic lesions, and very slow flow.