Incidentally Discovered ACTH-Secreting Pituitary Adenoma on a Sestamibi Scan in a Patient With Hyperparathyroidism

ABSTRACT Objective: Sestamibi scanning is performed to evaluate hyperparathyroidism; however, finding an adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma on a sestamibi scan is not common. Methods: A 49-year-old Caucasian female with increased thirst and urination and weight gain was referred for evaluation of primary hyperparathyroidism (pHPT). Her serum calcium and parathyroid hormone (PTH) levels were at the upper normal limit, and 24-hour urinary calcium was elevated. Sestamibi scan did not reveal a parathyroid adenoma, but showed increased uptake in the pituitary gland. Morning serum cortisol, 11 pm salivary cortisol levels, and 24-hour urinary free cortisol (UFC) levels were elevated on 2 occasions. Cortisol levels were only suppressed with an overnight 8-mg dexamethasone suppression test (DST) and not with 1- or 2-mg DST. Two magnetic resonance imaging (MRI) scans of the pituitary and pan-body computed tomography (CT) scan did not reveal an ACTH source. Inferior petrosal sinus sampling (IPSS) showed a central to peripheral ACTH ratio >3.0 with lateralization to the right, and an ACTH-producing corticotroph adenoma was then surgically confirmed. Results: We report the incidental discovery of an ACTH-secreting pituitary adenoma adenoma on a sestamibi scan in a patient with hyperparathyroidism. Conclusion: Pituitary incidentalomas on sestamibi scans performed to evaluate parathyroid abnormalities have been reported, but their secretory nature has not been studied. Further studies are therefore needed to clarify the role of sestamibi scanning in the diagnosis of imaging-negative pituitary Cushing disease. Abbreviations: ACTH adrenocorticotropic hormone DST dexamethasone suppression test pHPT primary hyperparathyroidism IPSS inferior petrosal sinus sampling MIBI methoxyisobutylisonitrile MRI magnetic resonance imaging PTH parathyroid hormone UFC urinary free cortisol