Pituicytoma with unusual histological features.

Pituicytoma is a rare low-grade glial neoplasm that originates in the neurohypophysis or infundibulum. Because of its rare occurrence, the morphology and differentiation of pituicytoma have not been fully clarified. Here, we report a case of pituicytoma with unusual histological features mimicking ependymoma, but exhibiting the diverse morphology and differentiation of pituicytoma. The 1.4 cm-sized suprasellar mass was incidentally found in the magnetic resonance image of a 42-year-old Korean woman who had had a traffic accident. Four years later, she presented with symptoms of hypopituitarism and the follow-up images revealed slight enlargement of the mass. After gross total resection, microscopic examination revealed oval to elongated cells with abundant eosinophilic cytoplasm arranged in a perivascular pseudorosette pattern and short interlacing fascicles. Pleomorphic tumor cells and Herring bodies were diffusely distributed within the tumor. Neither Rosenthal fibers nor eosinophilic granular bodies were identified. The tumor cells were immunohistochemically positive for glial fibrillary acidic protein, vimentin and S-100 protein, but negative for synaptophysin and adenohypophyseal hormones. The epithelial membrane antigen and CD99 were expressed with a paranuclear dot-like or membranous pattern in some tumor cells. Ultrastructural examination revealed that the tumor cells with intermediate filaments were closely apposed with intercellular junctions and frequent basal lamina production.