What is an Adrenal Myelolipoma?
An adrenal myelolipoma is a rare, benign, hormonally inactive tumor composed of mature adipose (fat) tissue and hematopoietic elements (bone marrow-like tissue) that requires no treatment or follow-up in most cases. 1, 2
Tumor Characteristics
Composition and Behavior:
- The tumor consists of mature lipomatous tissue mixed with hematopoietic elements that resemble bone marrow 2, 3
- These are biochemically nonfunctioning tumors—they do not produce hormones 3, 4
- Myelolipomas are definitively benign with no malignant potential 1
Clinical Presentation:
- Most myelolipomas are asymptomatic and discovered incidentally on imaging performed for unrelated reasons 2, 3, 4
- Symptoms occur only when tumors become large, typically presenting as abdominal pain, flank pain, or increasing abdominal girth from tumor bulk 2, 3
- Rare complications include spontaneous retroperitoneal hemorrhage or tumor necrosis 3
Location and Distribution:
- Usually unilateral (one-sided), but bilateral cases have been reported 4, 5
- Can occasionally develop in extraadrenal sites including the retroperitoneum, thorax, and pelvis 3
Diagnostic Features
Radiologic Identification:
- Myelolipomas are readily identified on CT imaging by their characteristic macroscopic fat content 1
- The presence of fat within the lesion on imaging is diagnostic and distinguishes myelolipomas from other adrenal masses 1
Important Caveat:
- While myelolipomas themselves are hormonally inactive, they can coexist with other hormonally active adrenal tumors or congenital adrenal hyperplasia 6, 3
- Hormonal evaluation is only necessary if there is clinical suspicion of a concomitant functional adenoma 6
Management Approach
No Follow-Up Required:
- Patients with myelolipomas and other small masses containing macroscopic fat detected on initial work-up do not require further follow-up imaging or functional testing, regardless of size 1, 6, 7
- This exemption from the typical 4 cm threshold for repeat imaging applies specifically because the fat content makes them definitively diagnosable as benign 6
- Patients can be reassured this is a benign finding requiring no treatment 6
Surgical Indications:
- Surgery is reserved for symptomatic tumors causing pain or mass effect 1, 3, 8
- Some sources suggest considering resection for very large tumors (>7 cm) even if asymptomatic, though this remains controversial 8
- Laparoscopic adrenalectomy is the preferred surgical approach when intervention is needed 5
Key Clinical Pitfall: