[Atypical computed tomographic features of meningioma: a case report].

Diagnosis of intracranial meningiomas with computed tomography (CT) is usually easy. However, some authors have reported cases preoperatively misdiagnosed because of atypical computed tomographic features. We report a case of non-cystic meningioma presenting a ring enhanced mass lesion, with CT scan. A 48-year-old male was admitted to our hospital on January 5, 1987, because of progressive monoparesis of his left lower limb. This had continued for 1 1/2 years. Neurological examination revealed monoparesis, hypesthesia and decreased deep sensation of the left lower limb. X-ray films of the skull appeared normal. A CT scan demonstrated a ring-like high density mass attached to the falx in the right frontoparietal area with perifocal low density. The ring-like high density was irregularly increased with contrast enhancement. Right carotid angiograms showed a doughnut like tumor stain without meningeal blood supply. Brain scintigrams revealed a dense round hot lesion in the frontoparietal area at 5 minutes, and the hot lesion was still visualized after 90 minutes. We diagnosed a cystic parasagittal meningioma. A right frontoparietal craniotomy was performed, and total removal of the parasagittal tumor was made. The center of the tumor was very soft but it could not be said that it was not cystic. Histologically the tumor was a meningotheliomatous meningioma. The center of the tumor, which was very soft, was necrotic with arteriolar hyalinization. The meningioma cells survived around the patent vessels. These intact meningioma cells were scattered like islands in extensive necrosis. This is so called "oasis phenomenon" indicating that the necrosis of the tumor was caused by intratumoral ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)