Pituicytoma - A distinctive low-grade glioma of the neurohypophysis

Pituicytoma is a rare, poorly characterized tumor of the sella and suprasel lar region that is distinct morphologically from other local tumors and is thought to be derived from neurohypophyseal pituicytes. Clinical data, neur oimaging studies, and microsections were reviewed from nine such low-grade gliomas. Immunostains for glial, neuronal, and proliferation markers were p erformed on all nine tumors and six control neurohypophyses. Three tumors w ere studied ultrastructurally. Six men and three women, age 30 to 83 years (mean, 48 years), presented with visual symptoms, headache, or hypopituitar ism. Magnetic resonance images showed solid, discrete, contrast-enhancing m asses, four within the sella and five in the suprasellar space. The tumors consisted of sheets and/or fascicles of plump spindle cells with slightly f ibrillar cytoplasm and slightly pleomorphic, oval-to-elongate nuclei with p inpoint nucleoli. Extracellular mucin was prominent in one tumor. Rosenthal fibers, granular bodies, and Herring bodies (granular axonal dilatations c haracteristic of the normal neurohypophysis) were lacking. Mitoses were rar e or absent. MIB-1 labeling indices were low (0.5-2%). Tumor cells were str ongly reactive for vimentin and S-100 protein, variably positive for glial fibrillary acidic protein, and nonreactive for synaptophysin and neurofilam ent protein. Cytoplasm varied in electron density and contained intermediat e filaments. Neither meningothelial nor ependymal features were noted. Two tumors recurred at 20 and 26 months after subtotal resection, but none of t he six completely resected tumors have done so. Pituicytomas are discrete, largely noninfiltrative low-grade gliomas of the sellar region that occur i n adults. Their histologic appearance is distinct From pilocytic and ordina ry, infiltrative astrocytomas. The distinction between pituicytoma and norm al neurohypophysis is aided by the latter's content of axons, Herring bodie s, and perivascular anucleate zones rich in axonal terminations. Although c urable by total excision, subtotal resection can be associated with recurre nce.