CT imaging characteristics of oncocytic adrenal neoplasms (OANs): comparison with adrenocortical carcinomas

Oncocytic adrenal neoplasms (OANs) are rare, but are an important subtype of adrenal tumors that is being diagnosed with increasing frequency. Unfortunately, the imaging characteristics of this tumor have not been well described. Our purpose was to identify CT features to differentiate OANs from adrenocortical carcinomas (ACC).

From 1991 to 2012, 18 patients with OANs were identified from our institution's pathology database. Twelve had CT examinations available for review. CT characteristics of five benign and seven malignant OANs were reviewed by two abdominal radiologists, and compared to ACC (n = 10). Morphologic characteristics and density measurements were recorded for each imaging phase. Absolute contrast washout was calculated and compared.

Benign OANs were smaller [mean size 3.7 cm (range 2.6-5.3)] and more homogeneous than malignant OANs and demonstrated greater washout [mean washout percentage 72.3% (range 61-88)]. Malignant OANs demonstrated features similar to ACCs, including size [mean 9.4 cm (range 5.2-9.8)] and internal necrosis (n = 6). Mean enhancement washout percentage for malignant OANs was 12% (range -8 to 32).

Benign OANs (oncocytomas) may be distinguished from lipid-rich adenomas on non-contrast CT but may be indistinguishable from lipid-poor adenomas. Malignant oncocytic neoplasms can demonstrate features similar to ACCs, including larger size, internal necrosis, and lower percentage enhancement washout.