How is FMD diagnosed?
Medical imaging is necessary to diagnose FMD. In case of symptoms suggestive of FMD, the recommended first-line imaging is CTA (Computed Tomographic Angiography) or MRA (MRI enhanced with contrast) if CTA is contraindicated.
Duplex ultrasound as a first-line diagnostic test may be an alternative in specialized centres with a large experience.
It may also bring complimentary information to assess the responsibility of an FMD-related stenosis in the onset of hypertension, and may assist with the decision on whether to proceed to an intervention to improve the blood flow to the kidney/s or not ( see below).
In many cases, duplex ultrasound is very useful for follow-up imaging, either by itself, or in conjunction with other types of imaging.
If the CTA or MRA doesn’t confirm a diagnosis, but a high level of suspicion still exists, catheter- based angiography (where a tube catheter is inserted into the artery, usually via the groin, and a contrast agent is used to better visualize the interior of the artery) may be considered.
The most typical radiological image seen (in 80-90% of cases) is a series of alternating stenosis and dilations that give the artery a “string of beads” appearance. This FMD subtype is classified as Multifocal FMD. Multifocal FMD lesions are most often seen in the mid- and distal (furthest from the aorta) segments of the artery.
In 10-20% of FMD cases, one single, or several isolated stenosis may be seen. In this case the diagnoses of FMD can only be made once other possible causes of arterial narrowing such as atherosclerosis, or other rare, inflammatory or genetic diseases have been ruled out. This subtype is classified as Focal FMD. Focal FMD lesions can be seen across the whole length of the artery, but in the case of a proximal (closest to the aorta) lesion, it may be difficult to differentiate from a stenosis caused by atherosclerosis.
Focal FMD is the form seen more commonly in children.