What is the recommended CT (Computed Tomography) scan order for a patient with a suspected adrenal myelolipoma?

Recommended CT Scan Order for Suspected Adrenal Myelolipoma

For a patient with suspected adrenal myelolipoma, a non-contrast CT scan of the abdomen should be ordered as the initial imaging study, as it can reliably identify the characteristic macroscopic fat within the lesion. 1, 2

Diagnostic Imaging Algorithm

1. First-line imaging:

   • Non-contrast CT abdomen
   • Look for: Characteristic fat density (negative Hounsfield units, HU < 10)
   • Macroscopic fat within the lesion is pathognomonic for myelolipoma 2

2. If initial non-contrast CT is indeterminate:

   • Proceed with contrast-enhanced washout CT
   • Parameters to assess: >60% washout at 15 minutes suggests benign lesion 1, 2

3. Alternative second-line imaging if needed:

   • Chemical shift MRI (if CT findings are equivocal)
   • Look for: Signal intensity loss in opposed-phase images 1, 2

Key CT Findings in Adrenal Myelolipoma

• Presence of macroscopic fat (negative HU values) is diagnostic 3
• May have heterogeneous appearance if containing varying amounts of myeloid tissue 4
• Size can range from small to large (reported cases from 2-9 cm) 3
• Predominantly right-sided in some case series, though can occur bilaterally 3, 5

Important Considerations

• Precontrast images are essential to avoid diagnostic errors 3
• Myelolipomas composed primarily of myeloid tissue may not show the typical fat density and can appear more heterogeneous 3, 4
• CT is superior to ultrasound for definitive diagnosis, as ultrasound findings can be variable (hyperechoic in fat-predominant lesions, hypoechoic in myeloid-predominant lesions) 3, 4

Management Based on Imaging Findings

• Myelolipomas <4 cm that contain macroscopic fat on initial imaging require no further follow-up imaging or functional testing 1, 2
• Myelolipomas ≥4 cm but radiologically benign should undergo repeat imaging in 6-12 months 1, 2
• Consider adrenalectomy if growth is >5 mm/year after repeating functional workup 1, 2
• No further imaging follow-up is required if growth is <3 mm/year on follow-up imaging 1
• Surgical removal may be indicated for symptomatic lesions or those exceeding 7 cm 6

Common Pitfalls to Avoid

• Failing to obtain precontrast images, which are essential for identifying fat density 3
• Misdiagnosing myeloid-predominant myelolipomas that may not show typical fat density 4
• Unnecessary follow-up imaging for small (<4 cm) myelolipomas with characteristic fat density 1, 2
• Overlooking the need to exclude functional adrenal disorders through appropriate hormonal evaluation, even though myelolipomas are typically non-functioning 2, 7

By following this approach, the diagnosis of adrenal myelolipoma can be established with high confidence, avoiding unnecessary additional testing or interventions for this benign condition.