Tumors of the adenohypophysis are the principal tumors of the sellar region, and also are among the most frequent primary intracranial neoplasms seen in clinical practice. They represent approximately 10-15% of all operated intracranial tumors. The overwhelming majority of neoplastic lesions arising in the adenohypophysis are adenomas. Diseases of the hypothalamus comprise tumors, inflammatory and infectious diseases, and genetic disorders. Tumors found in the hypothalamus and neurohypophysis include granular cell tumor, craniopharyngioma, germinoma, teratoma, meningioma, glioma. Inflammatory diseases include sarcoidosis, histiocytosis, etc. Infectious diseases such as meningitis (tuberculous, bacterial, viral or fungal) are also found in the hypothalamus and neurohypophysis. A rare and little-studied neoplasm occurring in this location, the pituicytoma or infundibuloma, is one of the few primary tumors of the neurohypophysis. The term pituicytoma was historically also used for other tumors in the sellar and suprasellar region (granular cell tumors, pilocytic astrocytomas), but this term is now reserved for low-grade glial neoplasms that originate in the neurohypophysis or infundibulum and that are distinct from pilocytic astrocytomas. To date, only a few microscopically proven cases have been reported in the literature (1, 2, 3, 4, 5, 6, 7, 8, 9, 10). Pituicytoma was believed pathologically to arise from the "pituicyte", a specialized glial cell of the neurohypophysis (5). Microscopically, pituicytomas have a solid, compact architecture and consisting almost entirely of elongate, bipolar spindle cells arranged in interlacing fascicles or in a storiform pattern. Tumors can show dense adherence to adjacent structures. Individual tumor cells contain abundant eosinophilic cytoplasm and cell shapes range from short and plump to elongate and angulated. There is no significant cytoplasmic granularity or vacuolization. Nuclei are of moderate size, oval-to-elongate, with little or no atypia. Mitotic figures are rare. Reticulin stain shows a perivascular distribution, intercellular reticulin being sparse. Important for the differential diagnosis with pilocytic astrocytoma and normal neurohypophysis, pituicytomas show no Rosenthal fibers or eosinophilic granular bodies. In this case, histological examination showed the characteristic of pituicytoma. Immunohistochemical staining of the tumors demonstrated diffuse, strong positive staining for S-100. The tumor cells were immunonegative for synaptophysin, patchy positive staining for glial fibrillary acidic protein(5, 6), and EMA(6). There was no immunostaining of tumor cells by Neu-n and Progesterone receptor. In summary, pituicytoma should be included as a rare differential diagnosis in patients with well-enhanced homogeneous lesions in the sellar.
Contributed by Yong Huang, MD, Juan Quan, MD, Hong Su, MD, Hai-xia Hu, MD, Feng Wang, MD