A spectrum of behaviour in silent corticotroph pituitary adenomas

Silent corticotroph adenomas (SCA) are pituitary tumours positive on immunohistochemical staining for ACTH but without clinical evidence of Cushing's disease in the patient. Previous reports suggest that these tumours may behave in a more aggressive way then other pituitary adenomas. We have followed the natural history of SCA and assessed whether histopathological indices predict tumour behaviour. We identified 22 patients in whom trans-sphenoidal surgery was performed for a non-functioning adenoma (NFA) with positive immunostaining for ACTH between 1990 and 2000 and examined the history of their disease. Patients were followed up for a mean of 4.8 years. A total of 86.7% of patients had documented visual deficits at presentation. In four cases hypercortisolaemia was observed later in the course of the disease. Two patients died as a result of their SCA and 33.3% of tumours recurred. Recurrence was more frequent in patients treated with adjuvant radiotherapy. Pathological indices (increased mitotic range and Ki-67) did not predict recurrence or malignant transformation. We suggest that certain 'silent' corticotroph tumours may have the potential for ACTH secretion leading to hypercortisolaemia at a later stage in the disease. The possibility of transformation to a more aggressive tumour needs to be considered in all SCA.