The pituicytoma is a rare neoplasm of the sellar region. As illustrated in our 2 cases, a number of features common to the pituicytoma help to distinguish it from other, more common, lesions of the sellar and suprasellar region, including pituitary adenoma, meningioma, and schwannoma (summarized in the ). Patients present with a discrete, solid sellar mass that is isointense to surrounding brain by T1-weighted MRI and homogeneously contrast enhancing after administration of gadolinium. Surgical resection is the primary treatment, and the tumors are often noted to be highly vascular and sometimes difficult to excise. On pathologic examination, the tumors are composed of bipolar spindle cells with round to elongate nuclei, in a fascicular arrangement, with rare mitotic activity. Immunohistochemistry demonstrates strong, diffuse S100 and vimentin staining; variable Bcl-2 and glial fibrillary acidic protein immunopositivity; and no immunostaining for synaptophysin, chromogranin A and B, and neurofilament. Ultrastructural analysis can assist in the diagnosis of these neoplasms.7,8
Unlike pituitary adenomas, there is an absence of definitive secretory granules. There is no significant accumulation of mitochondria, interdigitation of cell membranes, or accumulation of pericellular basal lamina. Occasional intermediate filaments can be identified.
Characteristic Features of Select Tumors in the Sellar/Parasellar Region
Our findings are consistent with those of other investigators and confirm the unique nature of this rare sellar neoplasm.1,3-5
Interestingly, we observed strong, diffuse immunopositivity for Bcl-2, an important regulator of apoptosis, in both tumor specimens. As shown in , Bcl-2 immunostaining of the normal pituitary gland is focal, and some authors4
have suggested that it is primarily restricted to folliculostellate cells of the adenohypophysis. Our findings, consistent with those of Ulm et al,4
raise the intriguing possibility that the pituicytoma may arise from folliculostellate cells. Alternatively, Bcl-2 expression in pituicytomas may represent an important factor in tumorigenesis, as has been found in other sellar neoplasms.9
To determine if pituicytomas are characterized by unique genetic alterations, we performed array CGH on tumor DNA isolated from patient 1. We identified multiple chromosomal imbalances including losses for chromosome arms 1p, 14q, and 22q and overrepresentation on chromosome arm 5p. Consistent with the notion that pituicytomas are a unique subset of tumors of the sellar region, the overall pattern of genetic alterations was unique when compared to 5 representative pituitary adenomas (data not shown) and previous reports10-12
of chromosomal imbalances in pituitary adenomas. Although the pattern of genetic changes was unique, it is interesting to note that some of the individual genetic changes in pituicytoma, including chromosomal imbalances on 1p, 5p, 14q, and less frequently 22q, have been reported in individual pituitary adenomas. This suggests that there may be some similarities in the mechanisms of tumorigenesis in sellar region neoplasms.
The histologic, ultrastructural, and genetic findings in this study support the unique identity of the pituicytoma. As this is the first report on genetic alterations in pituicytoma, we hope to both contribute to the knowledge of this neoplasm and stimulate future research on its tumorigenesis. Future studies are needed to (1) identify how common these chromosomal imbalances are in pituicytomas and to (2) elucidate critical genes in pathogenesis that may reside in these regions of copy number aberration.