Fibromuscular dysplasia
Updates to Article Attributes
Fibromuscular dysplasia (FMD) is a heterogenous group of vascular lesions characterised by a non-inflammatory, non-atherosclerotic angiopathy of medium-sized arteries.
Epidemiology
Most common in young women with a female to male ratio of 3:1. It typically is diagnosed between the ages of 30 and 50 4.
Clinical presentation
FMD is frequently asymptomatic. Symptomatic patients commonly present with hypertension due to renal artery stenosis, or less commonly renal impairment. They may also present ischaemia due to narrowing of other vessels, for example TIA s, stroke, dissection, or Horner syndrome.
Pathology
The exact cause is not well known. The underlying pathology is fibrous or fibromuscular thickening of the arterial wall. Any layer of the vessel wall may be affected: intima, media or adventitia. There is absence of inflammatory cells.
Classification
FMD is classified into 5 categories according to the vessel wall layer affected:
- intima: 5% 4
- 1: intimal fibroplasia
- media: 90-95% 4
- 2: medial fibroplasia (70%, commonest type)
- 3: medial hyperplasia (8-10%)
- 4: perimedial ( subadventitial ) fibroplasia (15-20%)
- adventitia: rare 4
- 5: adventital fibroplasia (1%)
The outcome is arterial stenoses. FMD most commonly causes small stenoses along a vessel with intervening areas of dilatation (small aneurysms), creating a “string of beads” appearance. Less commonly the stenosis has a smooth tapered appearance. FMD also weakens the vessel wall which predisposes to dissection.
Location
FMD may affect any medium sized artery in the body, and is commonly multifocal and bilateral (up to 60% when involving the renal arteries). FMD usually involves mid segment of the vessels and spares origins. Some sites are very frequently involved:
- renal arteries (one of the commonest sites of involvement)
- extracranial internal carotid arteries
- vertebral arteries
- iliac arteries
- mesenteric arteries
Complications
- spontaneous dissection
- distal embolisation (of thrombus formed in aneurysm)
- intra cranial aneurysms with or without SAH
- arteriovenous fistula
Radiographic features
Arterial imaging with CT angiography, MR angiography and digital subtraction angiography (DSA) may be used to visualise the lesions in FMD. Selective DSA is the gold standard because it allows visualisation of small or peripheral lesions. The characteristic finding is alternating stenoses and dilatations, causing a string of beads appearance 5. Less commonly in intimal type II, smooth tapering of affected vessel or dissection may be seen. In type III there may be eccentric diverticular out pouching. Cross-sectional imaging (CT and MRI) allows assessment of end-organ ischaemic damage.
Treatment and prognosis
Asymptomatic cases are only observed but if symptomatic then FMD responds well to angioplasty, with high long-term patency rates. A stent is generally not required.
Differential diagnosis
Imaging differential considerations include:
- atherosclerosis: usually at origin or proximal portion of artery
- vasculitis: elevated ESR +/- fever present
- traumatic/iatrogenic vascular injury: correlate with appropriate history
- segmental arterial mediolysis (SAM)
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