The radiographically diagnosed adrenal myelolipoma: what do we really know?

Purpose: Adrenal myelolipomas are uncommon, benign tumors of the adrenal glands that are not routinely evaluated for autonomous hormone secretion or followed by repeat imaging, but may lead to retroperitoneal hemorrhage. Little is known about the natural history these tumors with the majority of previous publications being confined to case reports and small case series. Methods: We reviewed the computed tomography (CT) reports of 62,279 patients evaluated at a tertiary referral center between 2002 and 2015 for the presence of an adrenal myelolipoma >1 cm in size. We then reviewed the CT imaging and patient charts to determine tumor size, growth, evidence of retroperitoneal hemorrhage, and endocrine dysfunction. Results: We identified 150 (0.24%) patients with 155 radiographically diagnosed adrenal myelolipomas found on a CT scan during our study period. The median tumor size at discovery was 2.1 cm. Twelve (7.7%) tumors were >6 cm. Sixty-nine (46%) patients had a follow-up CT with a mean time interval between scans of 3.9 years. Eleven tumors (16%) grew over our follow-up period with a median growth rate of 0.16 cm/year. No patient developed a retroperitoneal hemorrhage. Twenty (13%) patients underwent an evaluation for endocrine dysfunction. Three patients had evidence of hypercortisolism and one patient had primary aldosteronism. Conclusion: The majority of radiographically diagnosed adrenal myelolipomas found on abdominal CT imaging are small and slow growing. Retroperitoneal hemorrhage is uncommon, but the rate of associated endocrine dysfunction may be underestimated.