What is the recommended imaging approach for diagnosing fibromuscular dysplasia (FMD)?

Imaging Approach for Fibromuscular Dysplasia (FMD)

Catheter angiography is the gold standard for diagnosing FMD, but CTA should be used as the initial imaging modality for suspected FMD due to its high sensitivity and comprehensive assessment capabilities. 1, 2

Initial Diagnostic Approach

First-Line Imaging

• Computed Tomography Angiography (CTA)
  • Highest sensitivity (84.2%) among non-invasive modalities 2
  • Superior to MRA in visualizing vascular lesions in FMD 1
  • Allows comprehensive assessment from head to pelvis in a single session 2
  • Recommended protocol: full coverage from head to pelvis to detect all affected vascular territories 2

Alternative First-Line Option

• Magnetic Resonance Angiography (MRA)
  • Reasonable alternative with 62.5% sensitivity 2
  • Benefits: no radiation exposure, better soft tissue characterization 1
  • Particularly useful for younger patients where radiation exposure is a concern 2
  • Limited by lower spatial resolution than CTA 1
  • Contraindications: implanted metal, older pacemakers 1

Supplementary Imaging

• Duplex Ultrasonography
  • Recommended as a screening test but has limited sensitivity (28%) 2
  • Requires highly skilled technicians and interpreting physicians 1
  • Can identify corkscrew collateral vessels in some cases 1
  • Not reliable as a standalone test for FMD diagnosis 3

Definitive Diagnostic Imaging

• Catheter-based Angiography
  • Gold standard with superior spatial resolution (<0.1 mm) 1
  • Definitive test for equivocal cases on noninvasive imaging 1
  • Reserved for:
    • Inconclusive noninvasive imaging results 2
    • When intervention is planned during the same procedure 2
  • Caution: avoid in patients with congenitally weakened vessels (e.g., vascular EDS) due to risk of vascular perforation 1

Imaging Considerations by Vascular Territory

Renal Arteries

• Most common site of FMD (80% of cases) 2
• CTA has high sensitivity for detecting the classic "string-of-beads" appearance 4
• Consider pressure measurements during catheter angiography to assess physiologic significance 4

Cervicocranial Arteries

• CTA or MRA for initial assessment 2
• Digital subtraction angiography historically used but not recommended as initial screening due to procedural risks 1
• For brain aneurysm detection (common in FMD), multirow detector CTA is preferred with 82% sensitivity for aneurysms <3mm 1

Follow-up Imaging

• Annual noninvasive imaging (CTA or MRA) initially recommended 2
• More frequent imaging may be needed in first few years after diagnosis 2
• Consider alternating between CTA and MRA for long-term surveillance to reduce radiation exposure 2
• Frequency can be reduced once disease stability is confirmed 2

Common Pitfalls to Avoid

1. Incomplete imaging - FMD is a systemic disease; failure to image all relevant vascular beds may miss multifocal disease 2
2. Overlooking subtle findings - FMD findings may be subtle and missed if not specifically sought 1
3. Inadequate image reconstruction - Multiple reconstruction formats (multiplanar reformatted images, shaded surface display, maximum-intensity projections) are necessary for adequate evaluation 1
4. Relying solely on ultrasound - While useful as a screening tool, ultrasound has poor sensitivity (28%) compared to CTA (84.2%) 2, 3
5. Missing accessory renal arteries - MRA detects 96% of accessory renal arteries compared to only 5% with duplex ultrasonography 3

By following this imaging approach, clinicians can effectively diagnose FMD and develop appropriate management strategies for affected patients.