Giant somatotrophinoma without acromegalic features: more "quiet" than "silent": case report

"Silent" somatotrophinomas are very rare, typically large pituitary adenomas that present with mild or no acromegalic features despite positive immunostaining for growth hormone and autonomous (nonglucose-suppressible) growth hormone secretion. Because of this, they may be amenable to treatment with somatostatin analogues.

We report a giant somatotrophinoma (7 cm in maximal diameter) in a young woman with 6 years of amenorrhea who had no clinical features of acromegaly despite frankly elevated serum insulin-like growth factor 1 level at the time of diagnosis. Immunohistochemistry revealed focal strong positive staining for growth hormone in only 10% of the surgical specimen. Mutations in exons 8 or 9 of GNAS1, which are present in 40% of somatotrophinomas, were absent in the surgical specimen. The patient's clinical, biochemical, and radiological presentation is described and is compared with previously reported cases of silent somatotrophinomas.

Because of the size and visual symptomatology, partial resection was performed via a transcranial approach. External adjuvant beam radiotherapy was used. As insulin-like growth factor 1 levels remained elevated, treatment with somatostatin analogue is being pursued.

This case represents one of the largest somatotrophinomas described to date, and it demonstrates that serum insulin-like growth factor 1 should be measured even in the absence of acromegalic features in patients presenting with apparently nonsecreting macroadenomas. In addition to surgery and radiotherapy, somatostatin analogues may play an important role in controlling tumor growth.