Histopathological Review of Silent Pituitary Somatotroph Adenoma

Abstract

Silent pituitary somatotroph adenoma is an adenoma that expresses growth hormone (GH) and GH mRNA and has ultrastructural features common to somatotroph adenoma, without evidence of acromegaly. Forty-one silent somatotroph adenomas were reported in the literature, and their relatively common clinical symptoms include amenorrhea and/or galactorrhea. Random GH and insulin-like growth factor-1 levels are within normal in nearly half of the patients, whereas random PRL level is elevated in about 80% of patients. Generally, the GH immunostaining of silent somatotroph adenoma is weaker than that of classical somatotroph adenoma. Tissue culture studies indicate silent somatotroph adenoma has a very low basal secretory capacity of GH. Most of the silent somatotroph adenomas reported in the literature are sparsely granulated adenomas. The mechanism of silence may be attributed to unknown translational abnormalities of GH gene product, impaired secretion of GH, lack of biological activity of secreted GH, or it may represent an early stage of classical somatotroph adenoma. Meticulous endocrinological and histopathological examination may be helpful for the identification of silent somatotroph adenoma among patients with clinically non-functioning adenomas, especially female patients with amenorrhea and/or galactorrhea.