Faculty Bibliography

PURPOSE: To evaluate the role of T2*-weighted echo-planar perfusion imaging by using a first-pass gadopentetate dimeglumine technique to determine the association of magnetic resonance (MR) imaging-derived cerebral blood volume (CBV) maps with histopathologic grading of astrocytomas and to improve the accuracy of targeting of stereotactic biopsy. MATERIALS AND METHODS: MR imaging was performed in 29 patients by using a first-pass gadopentetate dimeglumine T2*-weighted echo-planar perfusion sequence followed by conventional imaging. The perfusion data were processed to obtain a color map of relative regional CBV. This information formed the basis for targeting the stereotactic biopsy. Relative CBV values were computed with a nondiffusible tracer model. The relative CBV of lesions was expressed as a percentage of the relative CBV of normal white matter. The maximum relative CBV of each lesion was correlated with the histopathologic grading of astrocytomas obtained from samples from stereotactic biopsy or volumetric resection. RESULTS: The maximum relative CBV in high-grade astrocytomas (n = 26) varied from 1.73 to 13.7, with a mean of 5.07 +/- 2.79 (+/- SD), and in the low-grade cohort (n = 3) varied from 0.92 to 2.19, with a mean of 1.44 +/- 0.68. This difference in relative CBV was statistically significant (P < .001; Student t test). CONCLUSION: Echo-planar perfusion imaging is useful in the preoperative assessment of tumor grade and in providing diagnostic information not available with conventional MR imaging. The areas of perfusion abnormality are invaluable in the precise targeting of the stereotactic biopsy

PURPOSE: Our purpose was to describe the MR imaging features in a series of spinal intramedullary gangliogliomas and to compare these findings with the MR features of intramedullary astrocytomas and ependymomas. METHODS: A retrospective analysis was performed of 76 MR examinations in 27 patients with histologically proved spinal ganglioglioma; these were then compared with imaging findings in a representative sample of histologically proved spinal cord astrocytomas and ependymomas. RESULTS: Statistically significant observations regarding spinal gangliogliomas included young age of the patients (mean, 12 years), long tumor length, presence of tumoral cyst, presence of bone erosion and scoliosis, absence of edema, presence of mixed signal intensity on T1-weighted images, and presence of patchy enhancement and cord surface enhancement. A trend (not statistically significant) was noted for holocord involvement and lack of magnetic susceptibility. CONCLUSION: Spinal ganglioglioma can be strongly suspected if MR images reflect the above criteria; however, the ultimate diagnosis still depends on radical resection and appropriate histopathologic investigation

PURPOSE: To assess the magnetic resonance (MR) imaging characteristics of spinal intramedullary ependymomas. MATERIALS AND METHODS: MR images obtained in 25 patients (aged 12-73 years) with proved intramedullary ependymomas were retrospectively reviewed. T1- and T2-weighted images were obtained in all patients. Gadopentetate dimeglumine was intravenously administered in 23 patients; enhanced sagittal and axial T1-weighted spin-echo images were reviewed. RESULTS: All tumors had hyperintense signal on T2-weighted images. In the 23 patients who received contrast material, all tumors became enhanced; enhancement was heterogeneous in 15 patients and homogeneous in eight patients. Twenty tumors had sharply defined, enhanced borders. Nineteen tumors were centrally located in the spinal cord. A hypointense rim on T2-weighted images was noted in five patients. CONCLUSION: Intramedullary ependymomas become enhanced after administration of gadopentetate dimeglumine; the enhanced borders are usually sharply marginated. They are characteristically located centrally in an expanded spinal cord. Hemosiderin is often present at the periphery of cervical ependymomas

We have previously shown that 5 mm axial T1-weighted images following Gd-diethylenetriamine pentaacetic acid (DTPA) administration were sufficient as a screening examination of the internal auditory canal (IAC) and cerebellopontine angle cistern in 80% of cases with sensorineural hearing loss. In the remaining 20% of cases 3 mm slices were necessary for confirmation of the diagnosis. To reduce the number of cases requiring the additional examination, we have modified our protocol to include a coronal 'scout' T1-weighted sequence followed by 5 mm axial sections angled through the IACs. Routine axial T2-weighted images of the posterior fossa were also obtained. One hundred eleven patients were studied with this protocol. In all but two of these the 5 mm sections unequivocally provided the diagnosis and in those two cases the coronal images confirmed the diagnosis suspected on the axial study. Three millimeter slices were not necessary in any patient. This three sequence, post-Gd-DTPA protocol, which requires only 12 min of scan time, is recommended as a screening protocol for IAC and cerebellopontine angle disease