Giant intracranial granular-cell tumor arising from the abducens

We present a case of an adolescent with a giant intracranial granular-cell tumor, who presented with diplopia and worsening visual acuity. The tumor measured 8.2 cm at the maximum diameter and occupied the right middle cranial fossa, with intrasellar and suprasellar involvement. It was composed of solid nests of oval or polygonal eosinophilic cells with a focal pseudo-papillary configuration. Pituitary macroadenoma was suspected from examination of the intraoperative frozen section, but immunohistochemical and ultrastructural findings were consistent with granular-cell tumor, and they suggested the origin to be the peripheral nerve sheath. Considering that abducens palsy was the first clinical manifestation, the tumor was thought to arise from abducens. From histological findings (focal cellular spindling, mitotic activity and a relatively high Ki-67 labeling index [10.1%]) and according to Fanburg-Smith's criteria, the tumor was suspected to have low-grade malignant potential. Granular-cell tumor should be included in the differential diagnosis of parasellar tumors, even in young patients or patients with large lesions. Both immunohistochemical and electron microscopic studies are essential for diagnosis.