Prolactin-cell adenoma with signet-ring cells: A case report

Objective: Signet-ring cell changes in the pituitary adenomas are extremely rare. To date, there have been only two reports documenting signet-ring cells in pituitary adenomas, one in a growth-hormone cell adenoma and the other in a nullcell adenoma. This report describes, for the first time, signet-ring cells in a prolactincell adenoma. Case history: The patient is a 46-year-old male who presented with severe headache and acute on chronic visual loss. Radiographic studies demonstrated a large cystic pituitary lesion with evidence of pituitary apoplexy. Laboratory values were consistent with a prolactin-cell adenoma. The patient underwent transsphenoidal resection of the prolactin-cell adenoma with significant post-operative improvement. Results: The tumor was composed of sheets of monomorphic round cells with conspicuous nuclei and granular cytoplasm, consistent with pituitary adenoma. Many cells had eccentric, often crescentic-shaped nuclei, imparting a signet-ring appearance and immunostaining was positive for prolactin, denoting an atypical prolactin-cell adenoma. The MIB-1 labeling index was slightly elevated. Electron microscopy demonstrated the presence of vacuolated areas in the cytoplasm that were not membrane bound and did not have specific inclusions. Discussion: This case augments the literature on pituitary adenomas with signet-ring cells. The clinical significance of signet-ring cells in pituitary adenomas is unknown. Accumulation of clinical cases, together with the advances in molecular techniques and experimental models, may yield further insight.