CYSTIC INTRACRANIAL SCHWANNOMA

The development of cystic components in intracranial schwannoma is not rare but has not been emphasized in any previous series or reviews. Cystic areas usually develop from coalescence of mucinous or microcystic areas in Antoni B tissue of the schwannoma. Hemorrhagic degeneration or necrosis due to the characteristic vascular abnormalities of these lesions may cause the formation of tiny cysts but not large ones. The formation of an associated arachnoid cyst and, rarely, the formation of cysts in glandular or pseudoglandular elements have also been reported. Awareness of the potential for partially or largely cystic schwannoma of the acoustic or trigeminal nerve is important for both the differential diagnosis and surgical planning. Surgically proven large cysts (occupying more than 50% of tumour volume) were detected preoperatively by computed tomography (CT) in 7 of the 35 cases of acoustic nerve schwannoma and both cases of trigeminal nerve schwannoma managed surgically at the authors' institution between 1980 and 1990. In a review of the literature the authors found descriptions of low-attenuation regions in CT scans for an average of 13% of acoustic and 29% of trigeminal nerve sheath tumours. Magnetic resonance imaging, ideally performed after intravenous administration of contrast material, also plays an important role in the detection and delineation of these tumour cysts,