Giant pituitary macroadenoma of stem cell origin: illustrative case

BACKGROUND: Giant pituitary macroadenomas with a diameter >4 cm are rare tumors, accounting for only about 5% of pituitary adenomas. They are more difficult to maximally resect safely owing to limited access as well as encasement of adjacent structures. Acidophil stem cell adenomas are rare immature neoplasms proposed to derive from common progenitor cells of somatotroph and lactotroph cells. These adenomas comprise about 4.3% of surgically removed pituitary adenomas. No previous reports have described acidophil stem cell adenomas that grow to the size of giant macroadenomas. This rare entity poses special challenges given the need for maximal safe resection in an immature neoplasm. OBSERVATIONS: The authors report a 21-year-old female who presented with 3 years of progressive visual decline and a giant macroadenoma. She underwent endoscopic transsphenoidal surgery for decompression. Given the tumor size and involvement of adjacent critical structures, gross-total resection was not achieved. The authors review the literature on giant pituitary adenomas and provide a discussion on clinical management for this rare entity. LESSONS: The authors present a very rare case of a giant pituitary adenoma of acidophil stem cell origin and discuss the technical and management challenges in this rare entity.