Neuroradiological findings of intracranial schwannomas not arising from the stems of cranial nerves.

Four cases of intracranial schwannomas not arising from the stems of cranial nerves are reported. All cases were confirmed by surgery and pathological examination. The related histogenesis and the CT and MRI findings are discussed, and the literature is reviewed. The CT and MRI findings of these tumours were analysed retrospectively and their pathological characteristics were reviewed. The tumours presented as heterogeneous hypointense to isointense mixed dense lesions with multiple areas of cystic degeneration and necrosis. Extensive cystic degeneration was the prominent characteristic on CT. The tumours showed hypointense to isointense signal on T(1) weighted images and heterogeneous hyperintense signal on T(2) weighted images. On contrast enhanced CT and MRI, the solid component and the wall of the tumours showed moderate to strong enhancement. Haematoxylin and eosin staining of the lesion demonstrated two histological patterns, Antoni type A and Antoni type B. Immunostaining showed intense immunoreactivity for S-100 protein. The CT and MRI findings of these tumours were similar to those of schwannomas arising from cranial nerves, although the former show a higher rate of cystic degeneration. Therefore, even when a mass is not in the usual cranial nerve region, if its imaging characteristics are similar to those of common schwannomas, the possibility of a schwannoma not arising from cranial nerve should be considered.