What type of CT (Computed Tomography) imaging should be ordered to assess for fibromuscular dysplasia?

CT Angiography from Head to Pelvis is the Preferred Imaging Modality for Fibromuscular Dysplasia

CT angiography (CTA) from head to pelvis is the recommended imaging modality for the assessment of fibromuscular dysplasia (FMD), as it provides the highest sensitivity (84.2%) among non-invasive techniques and allows comprehensive evaluation of multiple vascular beds in a single examination. 1

Rationale for CTA as First-Line Imaging

• CTA offers superior spatial resolution compared to other non-invasive modalities, allowing detailed visualization of:

  • The classic "string-of-beads" appearance in medial fibroplasia
  • Focal stenosis in intimal fibroplasia
  • Associated vascular complications (aneurysms, dissections)

• FMD should be considered a systemic arterial disease that can affect multiple vascular beds simultaneously, requiring comprehensive evaluation 1, 2

• The 2024 ESC guidelines specifically recommend CTA for the assessment of renovascular hypertension due to FMD 2

Imaging Protocol Considerations

The optimal CT protocol for FMD assessment should include:

1. Full coverage from head to pelvis - Since FMD is a systemic disease, comprehensive imaging is essential to detect all affected vascular territories 2, 1

2. Arterial phase contrast enhancement - Using iodinated contrast media (such as iodixanol) for optimal visualization of arterial abnormalities 3

3. Thin-slice acquisition - Typically 1-3mm collimation to maximize spatial resolution 4

4. Multiplanar reconstructions - Including:

   • Maximum intensity projections (MIP)
   • Volume rendering
   • Curved multiplanar reformats
   • These reconstructions are crucial and affect final assessment in 36-56% of cases 5

Diagnostic Yield and Clinical Impact

• Screening CTA of chest, abdomen, and pelvis in FMD patients shows substantial diagnostic yield, with studies demonstrating:

  • New areas of arterial beading in 49% of patients
  • Previously undetected aneurysms in 19% of patients
  • New dissections in 3% of patients 5

• The most commonly affected vessels are:

  • Renal arteries (67% of patients)
  • Lower extremity/iliac arteries (32% of patients) 5

Alternative Imaging Modalities

While CTA is preferred, other imaging options include:

1. MR Angiography (MRA):

   • Reasonable alternative with better sensitivity (62.5%) than ultrasound
   • Advantages: no radiation exposure, highly sensitive for brain parenchyma imaging
   • Limitations: lower spatial resolution than CTA, contraindicated with certain implants, longer scanning times 1, 2

2. Duplex Ultrasonography:

   • First-line screening test in some centers
   • Advantages: non-invasive, no radiation
   • Limitations: significantly lower sensitivity (28%) compared to CTA 1

3. Catheter Angiography:

   • Gold standard for diagnosis but more invasive
   • Reserved for cases with inconclusive non-invasive imaging or when intervention is planned 1

Common Pitfalls to Avoid

• Incomplete imaging: Failing to image all relevant vascular beds may miss multifocal disease. Since FMD is a systemic disease, CT or MRI angiography from head to pelvis is recommended 2

• Overlooking subtle findings: Less common presentations of FMD beyond the classic "string-of-beads" appearance include vascular loops, fusiform vascular ectasia, arterial dissection, and aneurysms 6

• Radiation exposure concerns: In younger patients (especially women), consider the cumulative radiation exposure from repeated imaging studies. When longitudinal follow-up is needed, consider alternating with MRA for surveillance 2

• Misinterpreting atherosclerotic disease as FMD: Careful evaluation is needed to distinguish FMD from atherosclerosis, particularly in older patients 7

In conclusion, CTA from head to pelvis represents the most comprehensive initial imaging approach for patients with suspected FMD, providing detailed anatomic information about the extent of disease and associated complications while guiding appropriate management decisions.