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Adrenal Myelolipoma (Myolipoma)



General Considerations

  • Rare, usually non-functioning tumors found incidentally most often in males aged 40-60
  • Benign tumors composed of fat and hemopoietic cells enclosed by pseudocapsule
  • Usually occurs in adrenal gland but may be extra-adrenal in 15%

Clinical Findings

  • Almost always asymptomatic
  • Most are discovered incidentally during a CT scan for other reasons
    • Adrenal masses are discovered incidentally in about 2.5-5% of abdominal CT scans
  • May be painful if there is hemorrhage

Imaging Findings

  • Unilateral
  • Usually small (<4 cm)
    • May be large in size (~10 com)
      • Hemorrhage is more common in larger lesions
    • Calcifications can occur in ¼ from prior hemorrhage
  • CT
    • Fatty mass of -30 to -115 HU
    • Fat interspersed with higher attenuation marrow-like elements
  • US
    • Mostly hyperechoic mass with interspersed hypoechoic regions
  • MRI
    • Heterogeneously high signal on T1
    • Intermediate intensity similar to spleen on T2
    • In opposed phase, there is a drop in signal intensity

Differential Diagnosis

  • Adrenal cysts
    • Water density with thin wall
  • Adrenal adenomas
    • Most are fat containing with densities of <10 HU
    • Density measurements before and after contrast administration can be used
      • Enhancement washout (HU portal venous phase minus HU delayed phase)/ HU portal venous phase x 100
      • If value is > 50%, adrenal adenoma
        • Sensitivity of 93% and specificity 98%

Treatment

  • Conservative with follow-up to determine if there is enlargement for masses >4 cm
  • Symptomatic masses are usually surgically removed

Complications

  • Occasionally associated with endocrine disturbances
    • Cushing’s syndrome
    • Conn’s syndrome
    • Addison’s disease
  • Acute hemorrhage may be associated with increase in size

adrenal myelolipoma,myolipoma

Adrenal myelipoma. Contrast-enhanced axial CT scan image through the upper abdomen reveals a large, partially fat-containing mass in the left adrenal glad (white arrow). The mass has a thin capsule surrounding it. A portion of the normal right adrenal is seen (red arrow).
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Kohli A. Adrenal Incidentilomas: Can we characterize them?. Indian J Radiol Imaging 2006;16:163-4