Adrenocortical carcinoma masquerading as Cushing's disease

Abstract

Cushing's syndrome (CS) can be classified as adrenocorticotropic hormone (ACTH)-dependent or ACTH-independent depending on the ACTH levels. However, 30% of the patients with CS have ACTH levels in the 'grey zone' (5-20 pg/mL), thereby posing a challenge in establishing the aetiological diagnosis. In a patient with full-blown features of Cushing's syndrome with equivocal ACTH levels, and a pituitary microadenoma on contrast-enhanced MRI sella, can falsely lead to a diagnosis of Cushing's disease. Pituitary microadenoma, if <6 mm in size, may be an incidental finding (incidentaloma) in this scenario and can be present in ∼3-27% of the healthy population. Therefore, in a patient with CS with equivocal ACTH levels and a pituitary microadenoma, multiple samplings for ACTH and adrenal imaging should be performed to exclude ACTH-independent CS and if required, bilateral inferior petrosal sinus sampling to determine the source of ACTH excess.

Figure 1

Contrast-enhanced MRI sella showing hypointense lesion on the left side of the pituitary measuring 5.5×4.3 mm.

Figure 2

Contrast enhanced computerised tomography (CECT) of abdomen showing heterogeneous enhancing mass lesion with arterial hypervascularity in the left suprarenal area measuring 10.7×8.6×11.3 cm.

Figure 3

Suggested strategy for the differential diagnosis and approach to a patient with Cushing's syndrome. ACTH, Adrenocorticotropic hormone; CRH, corticotropin releasing hormone; CD, Cushing’s disease; CS, Cushing's syndrome; HDDST, high dose dexamethasone suppression test; IPSS, inferior petrosal sinus sampling; IV, intravenous.