SAT-486 - Myelolipomas Are Not Always "Innocent": A Giant Functional Myelolipoma Causing ACTH-Independent Hypercortisolism

Introduction

Adrenal myelolipomas are uncommon benign adrenal tumors composed of mature adipose and hematopoietic tissue, accounting for approximately 3-4% of adrenal neoplasms. They are classically considered non-functioning and are most often discovered incidentally (1). Rarely, myelolipomas may be associated with autonomous cortisol secretion, a phenomenon that remains underrecognized. We present a rare case of a giant functional adrenal myelolipoma causing ACTH-independent Cushing syndrome, highlighting the importance of guideline-directed hormonal evaluation even in lesions with benign imaging characteristics.

Case Description

A 54-year-old woman was referred for obesity management following a prior sleeve gastrectomy and was incidentally found to have a progressively enlarging left adrenal mass measuring approximately 10 cm, with documented interval growth over several years. Her medical history included hypertension and prediabetes, without overt cushingoid features.
Biochemical evaluation demonstrated ACTH-independent hypercortisolism. A 1-mg overnight dexamethasone suppression test showed inadequate cortisol suppression, with morning cortisol of 11.6 µg/dL (normal < 1.8 µg/dL), suppressed ACTH ( < 5 pg/mL), and low DHEA-S. Screening for pheochromocytoma and primary aldosteronism was unremarkable.
Given tumor size, growth, and confirmed cortisol excess, she underwent laparoscopic left adrenalectomy (2). Pathology revealed a benign adrenal myelolipoma measuring 16.5 × 16.0 × 6.0 cm. Postoperatively, she lost 11 lb. ACTH stimulation testing confirmed postoperative adrenal insufficiency due to contralateral adrenal suppression, and physiologic hydrocortisone replacement was initiated.

Discussion

This case illustrates a rare but clinically significant functional adrenal myelolipoma causing ACTH-independent Cushing syndrome. Although typically regarded as non-functioning, myelolipomas may rarely exhibit hormonal activity, particularly when large or enlarging. Current adrenal incidentaloma guidelines emphasize systematic hormonal evaluation regardless of benign imaging features. This case reinforces that principle and highlights the risk of anchoring bias in patients with obesity and metabolic comorbidities.

References

(1) Ortiz Y, Mora G, Aviles A, Mangual M. #1705960 Unexpected Hyperfunctioning Adrenal myelolipoma: a rare cause of mild autonomous cortisol secretion. Endocrine Practice. 2024;30(5):S14. doi:https://doi.org/10.1016/j.eprac.2024.03.141

(2) Young WY, Kebebew E. UpToDate. Uptodate.com. Published 2025. Accessed December 22, 2025. https://www.uptodate.com/contents/evaluation-and-management-of-the-adrenal-incidentaloma?search=adrenal%20myelolipoma&source=search_result&selectedTitle=1~2&usage_type=default&display_rank=1#H26

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