Faculty Bibliography

In vitro studies provide a framework for understanding the biophysical mechanisms in the evolution of the magnetic resonance (MR) appearance of cerebral hematomas. Varying concentrations of oxyhemoglobin, deoxyhemoglobin and methemoglobin in saline or in concentrated bovine serum albumin solutions were imaged at 1.5 T, allowing assessment of the relative relaxation effects of heme oxidation state, oxygenation, and protein concentration. The findings demonstrate the importance of susceptibility effects arising from local field heterogeneity in producing T2 shortening upon varying hemoglobin concentration for intracellular deoxyhemoglobin and methemoglobin. Correlation between the clinically observed MR appearance of acute and subacute hematomas with these in vitro models is presented

Mood and behavioral changes have been reported in patients with thalamic tumors. We report a case in which an infiltrating mass lesion of both thalami was manifested by an alteration in personality with relative motor and sensory sparing. These personality changes, unlike many such cases reported in the literature, were not related to increased intracranial pressure and hydrocephalus. Magnetic resonance imaging (MRI) demonstrated the lesion that was subtle and nearly inapparent on contrast-enhanced computerized tomography (CT)

Routine evaluation of axial MR images of the cervical spine with high-intensity CSF (long TR/TE spin-echo or gradient-echo images) revealed apparent narrowing of the cord's anteroposterior diameter when these images were compared with corresponding postmyelography CT scans. This discrepancy was believed to be due to the truncation artifact at the CSF-cord boundary. To examine the truncation effect, we compared cord diameters in 12 patients on postmyelography CT scans and MR images and then compared these with MR scans of normal volunteers and of an agar-saline spine phantom. There was an artifactual diminution of the cord diameter in the 128-step phase-encoding axis of the 128 x 256-matrix MR scan as compared with the diameter of the cord in the patients' postiohexol CT scans and in the 256 phase-encoded axis MR scan in the volunteer study. A similar discrepancy was noted in the spine phantom study, in which the cord diameter in the 256-step phase-encoded MR scan, the CT scan, and direct measurement exceeded that in the 128-step phase-encoded axis MR scan. The range of differences between the measurements was as large as 2.3 mm (patients), 1.7 mm (volunteers), and 1.8 mm (phantom) for the three studies. In all three studies, varying the photographic window width and level produced variation in the apparent cord diameter of up to 1.5 mm. To eliminate this effect, the cord diameters in the phantom and the normal control subjects were measured at identical window levels. The truncation artifact, coupled with standard window settings used in photography, may lead to inaccurate display of the diameter of the cervical spinal cord

Forty patients with positive CSF cytology for subarachnoid dissemination of neoplasms were examined by magnetic resonance (MR) imaging for the detection of intracranial or intraspinal CSF metastases. The MR evidence of cerebral leptomeningeal metastases was noted in 12 of 54 unenhanced (22.2%) and 7 of 20 (35%) gadolinium-enhanced studies. However, in only 2 of the 20 (10%) gadolinium-enhanced scans did the enhanced brain images alone demonstrate the presence of CSF seeding. Four of 29 (13.8%) unenhanced studies of the spine and 6 of 16 (37.5%) gadolinium-enhanced spine studies were positive for neoplastic deposits on the spinal nerves or cord. Magnetic resonance without and with gadolinium enhancement was most likely to be positive in studies of patients with a non-CNS primary malignancy (16/51 = 31.4%) and least accurate with lymphoma or leukemia (1/18 = 5.6%). Although gadolinium administration increases the ability of MR to detect leptomeningeal metastases (particularly in the spine), the overall sensitivity of unenhanced and enhanced MR examinations is low (19.3 and 36.1%, respectively) in patients with proven cytological evidence of neoplastic seeding

Routine evaluation of axial MR images of the cervical spine with high-intensity CSF (long TR/TE spin-echo or gradient-echo images) revealed apparent narrowing of the cord's anteroposterior diameter when these images were compared with corresponding postmyelography CT scans. This discrepancy was believed to be due to the truncation artifact at the CSF-cord boundary. To examine the truncation effect, we compared cord diameters in 12 patients on postmyelography CT scans and MR images and then compared these with MR scans of normal volunteers and of an agar-saline spine phantom. There was an artifactual diminution of the cord diameter in the 128-step phase-encoding axis of the 128 x 256-matrix MR scan as compared with the diameter of the cord in the patients' postiohexol CT scans and in the 256 phase-encoded axis MR scan in the volunteer study. A similar discrepancy was noted in the spine phantom study, in which the cord diameter in the 256-step phase-encoded MR scan, the CT scan, and direct measurement exceeded that in the 128-step phase-encoded axis MR scan. The range of differences between the measurements was as large as 2.3 mm (patients), 1.7 mm (volunteers), and 1.8 mm (phantom) for the three studies. In all three studies, varying the photographic window width and level produced variation in the apparent cord diameter of up to 1.5 mm. To eliminate this effect, the cord diameters in the phantom and the normal control subjects were measured at identical window levels. The truncation artifact, coupled with standard window settings used in photography, may lead to inaccurate display of the diameter of the cervical spinal cord

Young children and infants normally have essentially no detectable brain iron. We evaluated brain iron patterns on 23 MR scans in 20 patients under 6 years of age with clinical and MR-documented cerebral infarctions in an attempt to further understand the neuropathologic phenomenon of increased iron deposition, which has been observed in other disease states. MR was performed at 1.5 T with spin-echo sequences from 1 day to 4 years after infarction. MR scans were interpreted without knowledge of clinical information and were assessed for (1) location and character (i.e., bland or hemorrhagic) of infarct, and (2) nonheme iron (i.e., marked hypointensity on long TR/TE images) in the basal ganglia, red nuclei, substantia nigra, thalami, dentate nuclei, and deep white matter. Sixteen of 20 infarctions were associated with increased iron. Six of seven cases with unilateral iron deposition had ipsilateral infarctions. The location (deep versus cortical) and age of the infarction had no apparent bearing on iron patterns. We conclude that increased brain iron is commonly associated with cerebral infarction and is nonspecific, rather than a marker of movement disorders. Since iron may arise from either interruption of transport pathways or directly from cell injury and, in fact, iron itself may propagate the tissue injury, this finding may have important clinical and pathophysiologic implications in ischemic brain injury

The Tolosa-Hunt syndrome consists of painful ophthalmoplegia caused by cavernous sinus inflammation, which is responsive to steroid therapy. The MR features of 11 patients with the clinical diagnosis of Tolosa-Hunt syndrome were studied. Two patients had normal MR studies of the orbit and cavernous sinuses. In nine patients, abnormal signal and/or mass lesions were seen in the cavernous sinuses; in eight cases, the abnormality was hypointense relative to fat and isointense with muscle on short TR/TE images and isointense with fat on long TR/TE scans. Extension into the orbital apex was seen in eight cases. In six of nine cases the affected cavernous sinus was enlarged; in five of nine it had a convex outer margin. One patient had a thrombosed cavernous sinus and superior ophthalmic vein in addition to a cavernous sinus soft-tissue mass. The signal intensity of Tolosa-Hunt syndrome in this limited series was similar to that of orbital pseudotumor and is confined to a limited differential diagnosis, which includes meningioma, lymphoma, and sarcoidosis

Thirty-four pediatric patients, twenty with presumed and fourteen with biopsy or autopsy proven brainstem gliomas were imaged by CT and MR before radiation therapy. Twenty-eight patients received radiotherapy. Of these, eighteen fit the protocol for combined clinical and MR post-treatment evaluation. No cases of radionecrosis were seen at autopsy. This study shows that MR can demonstrate tumor response to radiation therapy, tumor progression prior to clinical deterioration, post-treatment cyst formation and hemorrhage. Although MR clinical correlation was not optimal on six week post-treatment evaluation, 4-10 month post-treatment MR scanning correlated well with clinical evaluation. MR appears useful in post-therapeutic monitoring of tumor response