DIAGNOSIS AND DISCUSSION
Discussion: Pituicytomas are rare primary tumors of the neurohypophysis. The putative cell of origin is the pituicyte, which is a glial cell normally residing in the posterior pituitary and pituitary stalk, the function of which is thought to be the regulation of hormone secretion from the neurohypophysis. Alternatively, some authors have proposed the folliculostellate cell, an S100 expressing cell of the anterior pituitary, as the cell of origin. The natural history of the pituicytoma is not well understood due to their rarity, although the largest case series in recent years suggests that complete resection may be curative. However, there is a chance of recurrence following sub-total resection with the role of adjuvant therapies being uncertain at this time (2).
The histology of the current case is typical of a pituicytoma: fascicles of elongated, non-granular cells with a rich capillary network and little evidence of proliferation (1). Their immunohistochemical profile is that of S100 and GFAP expression, with variable expression of NSE and PGP9.5. The differential diagnosis includes granular cell tumor, however the cytoplasm of the former lacks granularity or PAS positivity. An astrocytoma (especially of a pilocytic nature) may be considered, but the pituicytoma lacks a biphasic growth pattern, Rosenthal fibers, or eosinophilic granular bodies. Meningioma is also a consideration, but one usually resolved by the absence of EMA expression and lack of meningothelial ultrastructural features. Finally, schwannoma may enter the differential diagnosis, but is ruled out by the GFAP expression and ultrastructural features.
Contributed by Julia Keith-Rokosh, Gary Ferguson and Robert Hammond