The development of Cushing's syndrome from a previously silent pituitary tumour.

A 60 year old woman originally presented with headache. Investigations revealed a pituitary tumour and endocrine investigations at that time showed normal plasma cortisol levels. Seven years after removal of this tumour, the patient developed the clinical and biochemical features of Cushing's disease. Immunoperoxidase staining of the original tumour was positive for adrenocorticotrophic hormone. This report suggests that immunocytochemistry may have an important role in the routine evaluation of pituitary tumours.