Abstract
Fibromuscular dysplasia (FMD), formerly called fibromuscular fibroplasia, is a group of nonatherosclerotic, noninflammatory arterial diseases that most commonly involve the renal and carotid arteries. The prevalence of symptomatic renal artery FMD is about 4/1000 and the prevalence of cervicocranial FMD is probably half that. Histological classification discriminates three main subtypes, intimal, medial and perimedial, which may be associated in a single patient. Angiographic classification includes the multifocal type, with multiple stenoses and the 'string-of-beads' appearance that is related to medial FMD, and tubular and focal types, which are not clearly related to specific histological lesions. Renovascular hypertension is the most common manifestation of renal artery FMD. Multifocal stenoses with the 'string-of-beads' appearance are observed at angiography in more than 80% of cases, mostly in women aged between 30 and 50 years; they generally involve the middle and distal two-thirds of the main renal artery and in some case also renal artery branches. Cervicocranial FMD can be complicated by dissection with headache, Horner's syndrome or stroke, or can be associated with intracerebral aneurysms with a risk of subarachnoid or intracerebral hemorrhage. The etiology of FMD is unknown, although various hormonal and mechanical factors have been suggested. Subclinical lesions are found at arterial sites distant from the stenotic arteries, and this suggests that FMD is a systemic arterial disease. It appears to be familial in 10% of cases. Noninvasive diagnostic tests include, in increasing order of accuracy, ultrasonography, magnetic resonance angiography and computed tomography angiography. The gold standard for diagnosing FMD is catheter angiography, but this invasive procedure is only used for patients in whom it is clinically pertinent to proceed with revascularization during the same procedure. Differential diagnosis include atherosclerotic stenoses and stenoses associated with vascular Ehlers-Danlos and Williams' syndromes, and type 1 neurofibromatosis. Management of cases with renovascular hypertension includes antihypertensive therapy, percutaneous angioplasty of severe stenoses, and reconstructive surgery in cases with complex FMD that extends to segmental arteries. The therapeutic options for securing ruptured intracerebral aneurysms are microvascular neurosurgical clipping and endovascular coiling. Stenosis progression in renal artery FMD is slow and rarely leads to ischemic renal failure.
Highlights
Disease name/synonyms Early descriptions of the disease used the terms fibromuscular hyperplasia or fibroplasia, but the term fibromuscular dysplasia (FMD) is used
85% of all FMD stenoses in the renal arteries are medial FMD; the lesion is a homogeneous collar of elastic tissue that presents as multiple stenoses interspersed with aneurismal outpouchings, with a preserved internal elastic lamina
A conservative conclusion is that multifocal stenoses with the "string-of-beads" feature is characteristic of FMD [3,4,10] and probably denotes the presence of the medial type FMD [3], whereas other angi
Summary
Screening tests The presence of renal artery FMD can be documented by the following non-invasive tests (in increasing order of accuracy): the captopril test, captopril renal scintigraphy, Doppler ultrasound, magnetic resonance angiography, gadolinium-enhanced magnetic resonance angiography, and computed tomographic angiography [37]. Patients with vascular Ehlers-Danlos syndrome, with the Williams syndrome, or with type 1 neurofibromatosis may have stenoses of renal and visceral arteries that mimic FMD The diagnosis of these conditions relies on associated phenotypic traits and genetic tests: acrogeric dysmorphy, distal joint laxity and tiny skin elasticity in vascular Ehlers-Danlos syndrome (confirmed by detection of COL3A1 gene mutations) [40]; facial dysmorphy, supraaortic stenosis and particular behavior in Williams syndrome (confirmed by detection of deletion 7q1.2 using FISH method) [41]; and specific skin lesions in neurofibromatosis 1 [42]. Revascularization is recommended for patients with hemodynamically significant renal artery stenosis – i.e. with bilateral stenoses or a unilateral stenosis causing more than 60% reduction in luminal diameter – and accelerated hypertension, resistant hypertension, malignant hypertension, hypertension with an unexplained unilateral small kidney, and hypertension with intolerance to medication [15] It is useful in young patients with recent-onset hypertension and hemodynamically significant renal artery stenosis due to FMD: in these cases the goal is to cure the hypertension. The major aims of current research are to unravel the pathophysiological mechanisms of FMD; to seek gene(s) that predispose to the condition; to assess more accurately the risk of disease progression in focal or multifocal FMD, http://www.OJRD.com/content/2/1/28 and in FMD affecting renal or extrarenal arteries; and to improve the detection and quantification of renal artery stenoses
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