What is the role of CT and MRI in the diagnosis of fibromuscular dysplasia (FMD)?

Updated: Jul 27, 2018
  • Author: James A Wilson, MD, MSc, FRCPC; Chief Editor: Helmi L Lutsep, MD  more...
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Answer

To the authors' knowledge, no large studies have been conducted to assess the sensitivity or specificity of CT angiography (CTA), time-of-flight (TOF) magnetic resonance angiography (MRA), or contrast-enhanced MRA (CE MRA) in the diagnosis of craniocervical FMD. However, these modalities, especially CTA and CE MRA, can show surprising vascular detail and may be sufficiently sensitive for the confident detection of FMD. Due to the risk of conventional angiography, there is certainly a need to identify comparably sensitive noninvasive imaging techniques. Fortunately, we have some clues from the renal literature that the above noninvasive techniques could be comparable.

CTA is continuously improving in resolution and may be used to detect the stenosis associated with FMD, but only recent-generation CTA equipment reliably shows sufficient detail to identify the classic string of beads pattern of most FMD cases. de Monye advocates the use of CTA as a noninvasive modality to diagnose FMD, albeit with only a series of 2 patients. [27] Regarding FMD of the renal arteries, the sensitivity of CTA has been compared directly with conventional angiography. [28] In their series of 21 patients with 40 total lesions identified on conventional angiography, all lesions were identified using several modalities of CTA (multiplanar reformatted images, maximum intensity projections, and shaded-surface display). Suspecting that CTA of the carotid arteries shares similar sensitivity to conventional angiography in identifying craniocervical FMD would be reasonable.

Findings on TOF MRA often suggest vessel stenoses, but this study has insufficient resolution to demonstrate a string-of-beads pattern suggestive of FMD.

Contrast-enhanced MRA will likely perform better than TOF MRA, but this has not yet been studied in detail regarding craniocervical FMD. However, similar to CTA, the renal literature has looked at FMD of the renal arteries using CE MRA. In a series of 25 patients, Willoteaux found the sensitivity and specificity of CE MRA in renal FMD to be 97% and 93% respectively. [29] They found 68% sensitivity in diagnosing stenosis, 95% in identifying the string of pearls, and 100% sensitivity in identifying an aneurysm. Thus, although CE MRA in craniocervical FMD has not specifically been assessed, it is likely that this modality is reasonably sensitive as compared with the more invasive criterion standard.

Conventional CT scanning and MRI may be useful in finding ischemic strokes caused by arterial dissection or the FMD lesions themselves. These modalities can also be useful in detecting subarachnoid hemorrhage.

CTA and MRA can often detect aneurysms greater than about 0.3 cm.


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