Metastases to the Pituitary Gland: Histological Patterns of Spread and Review of the Literature

Abstract

Few studies have focused on histological patterns of metastatic spread to the pituitary gland. We review our experience and that in the literature, 1970–present. Departmental cases, 1998–2021, were assessed for anterior versus posterior gland and/or capsular involvement and cohesive tumor obliterating underlying pituitary architecture versus metastatic cells filling pituitary acini with relative acinar preservation. Eleven autopsy/15 surgical cases, including 2 metastases to pituitary adenomas, were identified. Cohesive/obliterative patterns predominated histologically in both surgical and autopsy cases, but acinar filling by metastatic cells was extensive in 3/26 cases, focal in 5/26, and had resulted in initial erroneous impressions of atypical pituitary adenoma/pituitary carcinoma in 1 case and pituitary adenoma with apoplexy in another, likely due to focusing on necrotic areas in the specimen where the acinar pattern had been broken down and not appreciating nearby areas with acinar filling by metastatic cells. Although most pituitary metastases produce readily identifiable cohesive/obliterative patterns, diagnostic challenges remain with the less frequently seen “acinar filling” pattern. A dichotomy exists between patients with symptomatic pituitary metastases occurring early in the disease course and requiring surgical excision versus patients in whom asymptomatic small pituitary metastases are found incidentally at autopsy, the latter almost invariably in late disease stages, with widely disseminated metastatic disease.