الفهرس 
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Abstract
Aim of the work:
The clinical management and prognosis of patients with gliomas are dependant on accurate neuropathologic diagnosis. This necessitate tissue sampling and histologic classification. There is a potential of sampling error and improper grading with limited volume of tissues obtained through needle biopsies. The purpose of this study was to determine the accuracy of magnetic resonance imaging (MRI) for grading of giomas of astrocytic series, compared with neuropathologic findings at biopsy, and to explore whether MRI could enable correct determination of grading of cerebral gliomas and to evaluate the significance of different MRI features and the histologic limits of tumor cell invasion in untreated cerebral gliomas. Characteristics evaluated in MRI included boarder definition, mass effect, tumor signal heterogeneity, hemorrhage, calcium deposition, flow void caused by pathologic vasculature, cyst formation, edema, contrast enhancement, and crossing of the midline.
Conclusion:
MR offers definite advantages over CT in imaging of cerebral gliomas. The margins of astrocytomas are defined with much greater clarity by MR; they tend to be more diffuse than circumscribed when compared with CT characteristics. Anaplastic astrocytomas do not present typical or characteristic features on MR images. Anaplastic astrocytoma invariably appears larger on T2-weighted images than on CT scans. MR imaging can detect incipient glioblastoma at an earlier stage than CT, although very early stage glioblastoma are indistinguishable from astrocytomas. MR is more sensitive than CT is detecting infilteration of the corpus callosum. The following features have proven to be highly characteristic of glioblastoma multiforme:
(1) an irregular ring or garland pattern of contrast enhancement, (2) single or multible, irregular centeral areas of low attenuation representing necrosis, (3) typical site of occurrence. MR is far more sensitive than CT in the detection of oligodendrogliomas, but CT is more specific owing to its ability to demonstrate even small foci of calcification. Multifocal growth is better appreciated with MR. CT and MR provides complementary information in the diagnosis of oligodendrogliomas.
In the case of astrocytomas, we conclude that mass effect, cyst formation/necrosis, crossing of the middle line, and the degree of contrast enhancement appear to be the best predictor of high tumor grade. Marked edema and extensive contrast enhancement are signs of high cellularity and a more solid tumor. Tumor malignancy correlates with the amount of necrosis.
Hemorrhage occurs only in high-grade tumors. Measurements of MR tissue parameters have only limited value in characterization brain tumors.