What is the diagnosis and management of a right adrenal mielolipoma?

Adrenal Myelolipoma: Diagnosis and Management

Adrenal myelolipoma is a benign, non-functioning tumor composed of mature adipose and hematopoietic tissue that requires no further follow-up imaging or functional testing if it is less than 4 cm and contains macroscopic fat detected on initial imaging. 1

Diagnosis

Adrenal myelolipomas are rare benign tumors with an incidence of 0.1-0.2% in CT and autopsy series 2. They have distinctive imaging characteristics that typically allow for definitive diagnosis without biopsy:

• CT Imaging: The presence of macroscopic fat within the adrenal mass is pathognomonic for myelolipoma

  • Appears as well-defined mass with areas of fat density (negative HU values)
  • Non-contrast CT with HU < 10 indicates benign nature 3

• MRI: Chemical shift MRI can confirm the diagnosis

  • Signal intensity loss in opposed-phase images 3
  • High signal intensity on T1-weighted images in the fatty components

Management Algorithm

1. Size < 4 cm, asymptomatic, and contains macroscopic fat:

   • No further follow-up imaging or functional testing required 1
   • Simple observation is appropriate

2. Size ≥ 4 cm but radiologically benign:

   • Repeat imaging in 6-12 months 1, 3
   • If growth > 5 mm/year, consider adrenalectomy after repeating functional workup 1
   • If growth < 3 mm/year, no further imaging follow-up or functional testing required 1

3. Symptomatic myelolipoma (regardless of size):

   • Surgical resection is indicated for:
     • Flank or abdominal pain due to mass effect 2, 4
     • Hemorrhage within the tumor 2
   • Laparoscopic adrenalectomy is the preferred approach for benign lesions 3, 5

4. Large myelolipomas (> 6 cm):

   • Consider surgical resection due to increased risk of hemorrhage 2, 6
   • Both open and laparoscopic approaches are feasible depending on size and surgeon expertise 5, 6

Important Considerations

• Hormonal Evaluation: Although myelolipomas are typically non-functioning, a basic hormonal workup is recommended to exclude coexisting functional adrenal disorders 3, 4

  • 1mg overnight dexamethasone suppression test
  • Plasma or 24-hour urinary metanephrines
  • Aldosterone-to-renin ratio in hypertensive patients

• Differential Diagnosis: Must be differentiated from other fat-containing adrenal masses:

  • Adrenocortical carcinoma with fatty degeneration
  • Adrenal adenoma with fat content
  • Adrenal lipoma

Pitfalls to Avoid

1. Overtreatment: Not all myelolipomas require surgical intervention. Small (<4 cm), asymptomatic myelolipomas can be safely observed 1.

2. Misdiagnosis: Ensure proper imaging characterization before determining management. The presence of macroscopic fat is essential for diagnosis.

3. Overlooking complications: Large myelolipomas (>4-6 cm) have increased risk of hemorrhage and may warrant surgical intervention even if asymptomatic 2, 6.

4. Surgical approach: While laparoscopic adrenalectomy is feasible even for giant myelolipomas 5, very large tumors may require open surgery depending on surgeon experience and local resources.

5. Follow-up: For myelolipomas ≥4 cm that are not surgically removed, appropriate imaging follow-up at 6-12 months is necessary to monitor for growth 1, 3.