A Cryptic Cause of Cushing's Disease

Abstract

A 26-year-old woman with Cushing’s syndrome (CS), including hypertension, weight gain, and amenorrhea, had a 24-hour urine free cortisol value of 423 g (normal, 50 g) and endocrine testing consistent with Cushing’s disease (CD). Pituitary magnetic resonance imaging (MRI) (Figure 1A) suggested that a lesion on the left, inferior petrosal sinus sampling (IPSS) was consistent with CD, the ACTH concentrations were higher on the left, and she had exploratory surgery of the left side of the gland with removal of what was thought to be a microadenoma. Pathology was negative, and she remained hypercortisolemic. Postoperative MRI (Figure 1B) indicated only the site of the surgery (arrow), and a second IPSS was consistent with CD, but the ACTH concentrations from this procedure were higher on the right (in neither IPSS were the ACTH levels normalized to the concurrent prolactin levels). She then had repeat exploratory surgery, but no adenoma was found and CS continued. Three months later she was referred to the University of Virginia and a coronal MRI with thin cuts (1.2 mm) revealed a 5to 6-mm adenoma within the right cavernous sinus (Figure 1C, arrow), consistent with an ectopic parasellar microadenoma. At transsphenoidal surgery, a 5-mm microadenoma was found completely within the right cavernous sinus and was removed. It stained positive for ACTH. Her plasma cortisol and ACTH levels promptly dropped to subnormal levels (Figure 1D), and resolution of the clinical features of CS occurred over the next several weeks. In retrospect the adenoma could clearly be seen on all prior MRI but was in such an unusual location that it had been overlooked on the previous scans. This case highlights the importance of inspection of the parasellar regions in patients with CD and an MRI that demonstrates a normal pituitary (1).