[Perifocal abnormal signal intensity area in MRI in meningiomas]

To investigate the perifocal abnormal signal intensity area in MRI in meningiomas, we have analysed MRI in 10 cases among 73 meningiomas which were diagnosed by X-ray CT and verified by operation and pathology. The MRI scanners used in this study were Siemens Magnetom and Toshiba MRT 15A. Ten meningiomas diagnosed by MRI were as follows; one free convexity, one pyramidal, three falx and parasagittal, one sphenoid ridge, one olfactory groove, one cerebellopontine angle, two ventricular meningiomas. Perifocal abnormal signal intensity area was diagnosed as vasogenic edema in 4 cases. This area was shown as high signal intensity in T2-weighted MRI and was confined to the white matter. In proton density-weighted MRI, it was shown as high signal intensity and usually clearly distinguished from rather iso- or hypointensity tumor area. In T1-weighted MRI, this area was shown as slightly low signal intensity, which could be readily differentiated from the remarkably low intensity ventricular CSF. In one case a thin semi-lunar abnormal intensity area bordering the tumor was verified in MRI, but no abnormal area was shown in CT. In the remaining 6 cases, namely one free convexity, one pyramidal and two ventricular meningiomas, one cerebello-pontine and one sphenoid ridge meningioma, in which CSF abutted the tumor, abnormal signal intensity area was diagnosed as entrapped CSF space. The perifocal abnormal signal intensity area in MRI should be regarded as vasogenic edema or entrapped CSF space, and these two should be differentiated by the signal intensity, the distribution of the area and CT-cisternography.(ABSTRACT TRUNCATED AT 250 WORDS)