Imaging description

CT and MRI angiography provide a reliable and non-invasive method for diagnosis of renal fibromuscular dysplasia (FMD). The characteristic feature of renal FMD is a “string of beads” appearance of the mid- and distal renal artery due to the alternating stenosis and aneurysm formation (Figure 81.1). Axial imaging in combination with maximal intensity projection reconstructions are extremely helpful in making the diagnosis (Figure 81.2). Contrast-enhanced 3D MRA can also be used as an alternate to CTA (Figure 81.3). Care should be taken not to misinterpret the stepladder image reconstruction artifact, resulting from faulty data reconstruction that produces a gap or overlap between sections or from source images that are too thick, as FMD (Figure 81.4). Conventional angiography, although considered gold standard, is not frequently used due to its invasive nature and may be reserved for equivocal findings seen on CTA or MRA and for treatment.

Importance

Fibromuscular dysplasia is the second most common cause of renovascular hypertension, after atherosclerotic disease, affecting mostly young or middle-aged women. The disease is bilateral in two-thirds of the patients. It is classified according to the location of involvement within the vessel wall with medial fibroplasia accounting for 95% of cases. FMD is a non-inflammatory, non-atherosclerotic disease with presence of alternating areas of narrowing and small aneurysms causing the beaded appearance of the arteries. Vascular narrowing and dissections may occur. FMD may also involve other visceral arteries such as the hepatic artery as well as the carotid and vertebral arteries (Figure 81.5). Accurate diagnosis is important as the treatment of FMD is distinct from other causes of renal artery stensosis such as atherosclerotic disease or vasculitis and can be treated with percutaneous transluminal angioplasty with a very high success rate.

Typical clinical scenario

Renal FMD may be incidentally found on imaging in a young potential renal donor or in a young or middle-aged woman with hypertension refractory to medical therapy.