revolution of MR imaging in evaluation of posterior fossa tumors, is there still a value of CT examination in this respect, an initial-experience comparative study in Assiut University

Althrough a period of time extending from January to December 2001, fifty-one patients [32 males and 19 females] and of ages ranged from 2 months to 70 years were selectively included in our study for the clinical suspicion of posterior fossa space occupying lesions [SOL]. All patients submitted to full clinical assessment that was followed by a dual sitting radiologic work-up including CT scanning [using a Toshiba CT machine] and multiplanar MR imaging [using a Gyroscan MR machine] where comparison of the obtained CT and MR findings was performed depending on the proof obtained from final operative and histopathologic reports to assess the well-established role of the former [CT] to that of superadded latter procedure [MR] in the light of our experience in this respect. According to the histopathologic results, it was noted that cerebellar astrocytomas were the most frequent [18] ones representing 35.8% followed by 12 medulloblastomas [23.6%], 8 brain-stem gliomas [15.7%], 3 meningiomas [5.7%], 3 acoustic neuromas, 3 hemangioblastomas [5.7%], 2 ependymomas [3.9%] and 2 choroid plexus papillomas [CPPs] [3.9%]. It was noted that MR imaging has notably improved the tumour detectability regarding its borders and relation to the surrounding tissues that were sometimes improperly assessed on CT images due to petrous bones imaging artifacts and regarding its ability to detect the CSF seedlings of a tumour that was seen only on contrast-enhanced MR images in six of our patients due to its highest inherent resolution and soft tissue discrimination ability and to the unlimited multiplanar imaging capabilities, although detection of calcification is still a unique advantage of CT over MR imaging in this respect. In our study, the compared overall accuracy of MR to CT was 99.32% to 98.42% respectively. We concluded that when both procedures are available for usage, MR should be that of choice