Adrenocortical neoplasm of uncertain malignant potential with a myelolipomatous component

Macroscopic fat inside an adrenal lesion on CT is pathognomonic for myelolipoma, a benign neoplasm. Without macroscopic fat, it can be difficult to discern the nature of an indeterminate adrenal mass on imaging. One possible diagnosis for an indeterminate lesion without macroscopic fat is an adrenal oncocytic neoplasm (AON). Despite its typical benign presentation cases of malignant AON have been reported. Patients with malignant AON are often not surgical candidates and survival for unresected disease is 20%-35%. We present the third report of an AON of uncertain malignant potential (AONUMP) associated with a macroscopic fatty component with the largest reported size and longest duration of follow-up in the literature. This report details diagnostic and therapeutic challenges posed by AONUMP. This case highlights how pathognomonic radiographical findings associated with benign myelolipoma might mask rare, potentially malignant, lipomatous tumours.