Radiology of skull base neoplasms.

Computed tomography (CT) and magnetic resonance (MR) imaging are used routinely to stage skull base neoplasms preoperatively, define the extent of the tumor, identify perineural spread, plan surgery and radiation therapy, and evaluate the postoperative patient. Arteriography and interventional radiology also play a role in the identification and treatment of certain skull base neoplasms, particularly juvenile nasopharyngeal angiofibromas and paragangliomas. The skull base can be divided into three parts: anterior, central, and posterior. Pathology differs in each region, and CT and MR imaging often demonstrate characteristic imaging features suggestive of diagnosis.

Intracranial and spinal MR imaging findings associated with Krabbe's disease: case report.

Krabbe's disease is an autosomal recessive leukodystrophy with well-documented intracranial findings on both CT scans and MR images. We herein present what is thought to be the second case of Krabbe's disease with spinal involvement shown on MR images as abnormal contrast enhancement of the lumbosacral nerve roots. The typical intracranial findings of T2 hyperintensity without contrast enhancement were present within the periventricular white matter, but there was no area of abnormal signal intensity or enhancement within the substance of the spinal cord. We briefly review the pathophysiology, clinical presentation, and imaging findings of Krabbe's disease. Spinal abnormalities may precede the onset of brain abnormalities, and MR imaging may be a useful diagnostic tool in cases of Krabbe's disease and other leukodystrophies.

High b-value diffusion-weighted MRI of normal brain.

PURPOSE: As MR scanner hardware has improved, allowing for increased gradient strengths, we are able to generate higher b values for diffusion-weighted (DW) imaging. Our purpose was to evaluate the appearance of the normal brain on DW MR images as the diffusion gradient strength ("b value") is increased from 1,000 to 3,000 s/mm2. METHOD: Three sets of echo planar images were acquired at 1.5 T in 25 normal subjects (mean age 61 years) using progressively increasing strengths of a diffusion-sensitizing gradient (corresponding to b values of 0, 1,000, and 3,000 s/mm2). All other imaging parameters remained constant. Qualitative assessments of trace images were performed by two neuroradiologists, supplemented by quantitative measures of MR signal and noise in eight different anatomic regions. RESULTS: As gradient strength increased from b = 1,000 to 3,000, both gray and white matter structures diminished in signal as expected based on their relative diffusion coefficients [calculated average apparent diffusion coefficient (ADC) values: gray matter = 8.5 x 10(-4) mm2/s, white matter = 7.5 x 10(-4) mm2/s]. The signal-to-noise ratios for the b = 1,000 images were approximately 2.2 times higher than for the b = 3,000 images (p < 0.0001). As the strength of the diffusion-sensitizing gradient increased, white matter became progressively hyperintense to gray matter. Relative to the thalamus, for example, the average MR signal intensity of white matter structures increased by an average of 27.5%, with the densely packed white matter tracts (e.g., middle cerebellar peduncle, tegmentum, and internal capsule) increasing the most. CONCLUSION: Brain DW images obtained at b = 3,000 appear significantly different from those obtained at b = 1,000, reflecting expected loss of signal from all areas of brain in proportion to their ADC values. Consequently, when all other imaging parameters are held constant, b = 3,000 DW images appear significantly noisier than b = 1,000 images, and white matter tracts are significantly more hyperintense than gray matter structures.