Fibromuscular dysplasia
Updates to Article Attributes
Fibromuscular dysplasia (FMD) is a heterogenous group of vascular lesions characterised by an idiopathic, non-inflammatory, and non-atherosclerotic angiopathy of small and medium-sized arteries 7.
Epidemiology
The prevalence is unknown 7. 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 transitory ischaemic attacks, 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 1-4,7.
Classification
FMD is classified into five categories according to the vessel wall layer affected:
- intima: 5%
4-
1:
-
- media: 90-95%
4-
2:fibroplasiadysplasia (70%, commonest type) 3:medial hyperplasia (8-10%)-
4:perimedial (subadventitial) fibroplasia (15-20%) - medial hyperplasia (8-10%)
-
- adventitia: rare
4-
5:
-
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)
- intracranial aneurysms +/- subarachnoid haemorrhage
- 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, particularly in more common intimal subtype, 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. Inand adventitial type III, there may be eccentricis focal concentric, long-segment tubular stenosis or diverticular outpouching present. Cross-sectional imaging (CT and MRI) allows assessment of end-organ ischaemic damage.
- typical angiographic features include: vascular loops, fusiform vascular ectasia and a string of beads
- less typical features include: arterial dissection, aneurysm and subarachnoid haemorrhage
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)
- vasospasm
-<li>intima: 5% <sup>4</sup><ul><li>-<strong>1:</strong> intimal fibroplasia</li></ul>- +<li>intima: 5% <ul><li>intimal fibroplasia</li></ul>
-<li>media: 90-95% <sup>4</sup><ul>-<li>-<strong>2:</strong> medial fibroplasia (70%, commonest type)</li>-<li>-<strong>3:</strong> medial hyperplasia (8-10%)</li>-<li>-<strong>4:</strong> perimedial (subadventitial) fibroplasia (15-20%)</li>- +<li>media: 90-95% <ul>
- +<li>medial dysplasia (70%, commonest type)</li>
- +<li>perimedial (subadventitial) fibroplasia (15-20%)</li>
- +<li>medial hyperplasia (8-10%)</li>
-<li>adventitia: rare <sup>4</sup><ul><li>-<strong>5:</strong> adventitial fibroplasia (1%)</li></ul>- +<li>adventitia: rare <ul><li>adventitial fibroplasia (1%) <sup>8</sup>
- +</li></ul>
-</ul><h4>Radiographic features</h4><p>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 <a href="/articles/string-of-beads-sign">string of beads</a> appearance <sup>5</sup>. Less commonly in intimal type II, smooth tapering of affected vessel or dissection may be seen. In type III there may be eccentric diverticular outpouching. Cross-sectional imaging (CT and MRI) allows assessment of end-organ ischaemic damage.</p><ul>- +</ul><h4>Radiographic features</h4><p>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, particularly in more common intimal subtype, is alternating stenoses and dilatations, causing a <a href="/articles/string-of-beads-sign">string of beads</a> appearance <sup>5</sup>. Less commonly in intimal and adventitial type, there is focal concentric, long-segment tubular stenosis or diverticular outpouching present. Cross-sectional imaging (CT and MRI) allows assessment of end-organ ischaemic damage.</p><ul>
References changed:
- 8. Olin JW. Recognizing and managing fibromuscular dysplasia. Cleve Clin J Med. 2007;74 (4): 273-4, 277-82. <a href=http://www.ncbi.nlm.nih.gov/pubmed/17438676">Pubmed citation</a><span class="auto"></span>
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