Cushing's syndrome caused by an ectopic pituitary adenoma of the sphenoid sinus: Adrenal crisis after partial resections of the adenoma.

A 60-year-old woman with an 8-year history of Cushing's syndrome was evaluated. Biochemical data were consistent with those of Cushing's disease. Plasma ACTH levels responded paradoxically to GnRH. MRI demonstrated a large tumor occupying the sphenoid sinus, which was enhanced by gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). The pituitary gland was normal in shape and was located in the sella turcica without dislocation. The pituitary gland and the sphenoid tumor could be distinguished by the obvious difference in their MRI intensities. Three consecutive partial resections of the sphenoid tumor were performed, but plasma ACTH and cortisol levels remained high just after the third operation. Histological studies revealed a chromophobe adenoma immunohistochemically positive for ACTH. However, adrenal crisis occurred 3 months after the third operation during reserpine administration ( 1.5 mg/day for approximately 2 mo) for the treatment of Cushing's syndrome due to the residual tumor in the sphenoid sinus. Subsequent MRI showed no change in the tumor shadow, and the paradoxical response of plasma ACTH levels to GnRH remained unchanged. The fourth operation reconfirmed the existence of the ACTH-producing adenoma in the sphenoid sinus. There was no anatomical interaction between the sphenoid tumor and the pituitary gland, and, histologically, no tumor cells were present in the pituitary gland. These findings suggest that the tumor is an ACTH-producing ectopic pituitary adenoma arising from the sphenoid sinus. The patient has been in remission for 4 years on glucocorticoid replacement therapy. The factors responsible for the adrenal crisis were not well understood, although reserpine administration might have had some role.