What is an Adrenal Myelolipoma?
An adrenal myelolipoma is a definitively benign, non-functional tumor composed of mature adipose (fat) tissue and hematopoietic (bone marrow-like) elements that requires no treatment or follow-up in most cases. 1
Tumor Characteristics
- Myelolipomas have absolutely no malignant potential and are considered completely benign neoplasms. 1
- The tumor consists of mature adipose tissue interspersed with bone marrow-like hematopoietic elements in varying proportions. 2, 3
- These lesions are typically non-functional and do not secrete hormones, though rare exceptions have been reported. 3, 4
- Myelolipomas occur predominantly in adults and are frequently asymptomatic in approximately half of cases. 5
Diagnostic Features
- The presence of macroscopic fat within the adrenal lesion on CT imaging is diagnostic and definitively distinguishes myelolipomas from other adrenal masses. 1
- Myelolipomas are readily identified by their characteristic fat content on standard CT imaging without requiring additional testing. 1
- The fat component appears as low attenuation (negative Hounsfield units) on unenhanced CT scans. 6
Clinical Presentation
- Most myelolipomas are discovered incidentally during imaging performed for unrelated reasons (adrenal incidentalomas). 2, 3
- When symptomatic, patients may present with chronic abdominal pain, back pain, or symptoms related to mass effect from large tumors. 2, 3
- Hemorrhage within a myelolipoma is an uncommon complication that can cause acute symptoms. 2
- Despite being considered non-secretory, a complete hormonal evaluation should still be performed as approximately 5% of radiologically benign incidentalomas have subclinical hormone production. 7
Management Approach
Patients with myelolipomas detected on initial imaging workup do not require any further follow-up imaging or functional testing, regardless of size. 6, 1 This represents a critical distinction from other adrenal masses, where size-based surveillance is typically recommended.
Conservative Management (Preferred)
- Observation without intervention is appropriate for asymptomatic myelolipomas of any size. 1
- No repeat imaging or hormonal testing is necessary once the diagnosis is established radiologically. 6, 1
Surgical Indications
Surgery should be reserved only for: 1, 3
- Symptomatic tumors causing pain or significant mass effect
- Lesions causing complications such as hemorrhage
- Bulky masses (some sources suggest >7 cm) causing symptoms 3
Surgical Approach When Indicated
- Minimally invasive surgery (laparoscopic or retroperitoneoscopic adrenalectomy) should be performed when feasible. 7
- Complete hormonal evaluation including pheochromocytoma screening must be performed before any adrenalectomy to prevent intraoperative hypertensive crisis. 7
Important Clinical Pitfalls
- Do not subject patients with radiologically confirmed myelolipomas to unnecessary surveillance imaging or repeated hormonal testing. 6, 1 This is a common error that leads to patient anxiety and healthcare waste.
- The NCCN guidelines specifically exempt myelolipomas from the size-based surveillance protocols applied to other adrenal incidentalomas. 6, 1
- While generally non-functional, always perform initial hormonal screening as rare cases of hormone secretion have been documented. 4
- Adrenal biopsy should never be performed when myelolipoma is suspected based on imaging characteristics. 7