Prolactin-producing pituitary adenoma with atypical spindle cell morphology: a case report

Reported herein is a 25-year-old woman who was treated for a large and highly atypical prolactin-producing pituitary adenoma. On presentation, she exhibited right hemiparesis and left-sided visual loss, associated with amenorrhea. A massive (>5 cm) intra- and suprasellar lesion was seen on imaging, and her serum prolactin level was 4408 ng/ml. The patient received dopamine agonist treatment preoperatively for 4 weeks. To resect the tumor, a two-stage excision was required. Histologically, the specimen was composed of polygonal or spindle cells showing marked nuclear pleomorphism and/or multinucleation. Fibrosis was also focally conspicuous. Differential diagnoses included pituitary adenoma, pituitary carcinoma, pituicytoma, paraganglioma, spindle cell oncocytoma, and meningioma. Immunohistochemically, the tumor cells were positive for prolactin, chromogranin-A, and synaptophysin, but were negative for glial fibrillary acidic protein, S-100 protein, epithelial membrane antigen, and vimentin. No apparent cerebrospinal or systemic metastases are found. Ultimately, prolactin-producing pituitary adenoma was diagnosed. Our case highlights the difficulty in definitively diagnosing an unusual prolactin-producing adenoma based on histopathology alone and the importance of referring to clinical information and immunohistochemical findings when deriving the diagnosis.