Adrenal myelolipomas are benign, nonfunctional adrenal neoplasms predominantly composed of mature adipose tissue and intermixed myeloid tissue. They comprise 6% to 16% of all adrenal incidentalomas and are the second most common cause of adrenal lesions after adrenal adenomas.
The increased prevalence of adrenal myelolipomas is primarily due to markedly increased detection because of the wider accessibility and usage of computed tomography (CT) and magnetic resonance imaging (MRI) scans for unrelated reasons. The pathogenesis of adrenal myelolipoma is believed to either be due to metaplastic change in the mesenchymal cells or to overstimulation by adrenocorticotrophic hormone (ACTH).
Clinically, they are usually small and asymptomatic but may present with abdominal pain, nausea, or vomiting. On CT scan, they appear as well-circumscribed, hypodense masses with an attenuation of 90 to 120 Hounsfield units (HU) or lower, depending on their fat content.
Myelolipomas are rarely encountered outside the adrenal glands and are termed extra-adrenal myelolipomas, most often found in the retroperitoneum, thorax, or pelvis. Surgical resection is indicated in cases of significant adrenal neoplasm growth (>1 cm in defined time period), size >7cm due to chance of rupture and bleeding, symptomatic pain or mass effect, suspicion of malignancy, or hormonal hypersecretion.
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