Metamorphosis of a non-functioning pituitary adenoma to Cushing's disease.

Silent pituitary adenomas occur in 25-40% of all clinically apparent pituitary tumours. However, the subsequent development of florid Cushing's disease in a patient with a previous non-functioning tumour is extremely rare. We describe a 47 year-old woman presenting initially with a large, invasive and recurrent, non-functioning pituitary tumour. Histopathologic study of the initial tissue did not stain for any hormones. Six years after the initial presentation, she manifested florid ACTH dependent Cushing's syndrome. A recurrent invasive pituitary macroadenoma necessitated a third transphenoidal surgery. The resected specimen, in this instance, revealed positive staining for ACTH, FSH, prolactin, and growth hormone on immunocytochemistry. An incomplete response to surgical, radiation and medical therapy necessitated a bilateral adrenalectomy to control the hypercortisolism, which resulted in remarkable clinical improvement. We also review five previous case reports from the published literature of similar transformations from non-secreting pituitary adenomas to Cushing's disease. This subset of patients may represent yet another entity in the widening spectrum of Cushing's syndrome.