Adrenal myelolipomas account for 3.3-6.5% of adrenal masses and are typically unilateral, non-secreting tumors. It is diagnosed incidentally via imaging in most cases. The pathogenesis of adrenal myelolipoma is a subject of controversy. In some studies, elevated adrenocorticotropic hormone is believed to be associated with the development of adrenal myelolipoma.

We reported a 59-year-old man who was incidentally diagnosed a 8.3 cm right adrenal nodule without symptoms during a health examination. His baseline adrenocortical function showed normal level of serum cortisone 15.93 μg/dL(normal range: 9.52~26.21 μg/dL) and normal serum level of ACTH 37.51 pg/mL(normal range: 19.6 - 49.7pg/mL). The low-dose dexamethasone test was positive, and Cushing's disease was suspected after the high-dose dexamethasone test(cortisol level 4.42 μg/dL). The sellar MRI revealed a pituitary macroadenoma. After undergoing right adrenalectomy, his serum cortisol level was 18.09 μg/dL(normal range: 9.52-26.21 μg/dL), and it did not decrease from baseline. An endoscopic endonasal approach to remove the pituitary macroadenoma was performed one week later. The follow-up serum cortisol level decreased to 7.58 μg/dL(normal range: 9.52-26.21 μg/dL). The final pathology report revealed right adrenal myelolipoma and pituitary adenoma, respectively.

A previous study reported that myelolipomas larger than 6 cm were associated with a higher incidence of bleeding events[6]. Although Cushing's disease was confirmed, we arranged adrenalectomy for our patient because of the large tumor size. In this retrospective study of 92 myelolipomas evaluated for adrenocortical function, 3.3% of patients had autonomous cortisol secretion, attributed to a concomitant adrenal adenoma. Se Yoon Park et al. (2017) presented a case of pathologically confirmed bilateral adrenal myelolipoma associated with Cushing's disease. The pathogenesis of adrenal myelolipoma is multifactorial, with excess adrenocorticotropic hormone (ACTH) production in Cushing's disease representing one etiologic factor. A comprehensive adrenal function assessment may be considered at the time of diagnosis of an adrenal myelolipoma.

Cushing's disease should be considered in cases of adrenal nodules when Cushing’s syndrome is suspected.