Fibromuscular Dysplasia Pathology
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Direct answer
A "string of beads" along the mid and distal renal artery, sparing the origin, is the angiographic signature of fibromuscular dysplasia — a non-atherosclerotic, non-inflammatory disease of medium-sized arteries that predominantly affects women aged 15 to 50. In the renal artery it is the second commonest cause of renovascular hypertension after atherosclerosis; in the carotid and vertebral arteries it causes mid-cervical stenosis, dissection, aneurysm and, occasionally, the Horner syndrome of a carotid dissection. The medial fibroplasia variant accounts for the great majority of cases and produces alternating webs of collagen and segments of medial thinning — hence the beads. Unlike vasculitis, the erythrocyte sedimentation rate and C-reactive protein are normal, and unlike atherosclerosis the lesions sit away from the ostium; percutaneous angioplasty, usually without stenting, can cure the hypertension outright.
What you must remember
- Definition in one line: idiopathic, non-inflammatory, non-atherosclerotic fibrous thickening of medium-sized arterial walls, most often renal, then carotid-vertebral, with women of reproductive age making up the great majority.
- Histological variants: medial fibroplasia (about 80 per cent, the string of beads), perimedial fibroplasia (beads with smaller diameters), intimal fibroplasia (younger patients, smooth focal webs) and the rare adventitial form — the exam expects medial fibroplasia as the answer to "which type is commonest".
- Renovascular consequences: renin-mediated hypertension, often severe or resistant, with a bruit over the flank; a small kidney with a preserved cortical margin on imaging (contrast atrophy from large-vessel stenosis, unlike the patchy cortical scarring of reflux).
- Cerebrovascular consequences: mid-distal internal carotid and vertebral artery stenoses, spontaneous dissection (a recognised cause of stroke in young adults, sometimes with painful Horner syndrome), and intracranial aneurysm association warranting screening of the cerebral circulation.
- The negative tests that matter: normal inflammatory markers, no thrombotic or embolic screen positivity — the separation from vasculitis that examiners phrase as "fibromuscular dysplasia is not an arteritis".
- Location versus atherosclerosis: atherosclerosis narrows the renal ostium and proximal third in older patients with vascular risk factors; fibromuscular dysplasia involves the mid and distal artery in young women — the single most examinable contrast in the topic.
- Treatment logic: percutaneous transluminal renal angioplasty, with stenting reserved for dissection or elastic recoil; cure of hypertension is likelier when hypertension is short-standing; smoking cessation and screening of other vascular beds complete the plan.
The young hypertensive, worked through
A 27-year-old woman has had hypertension for two years, now on two drugs; examination reveals an epigastric bruit and her serum creatinine is normal. The secondary-hypertension sieve opens: renal artery stenosis (atherosclerotic or fibromuscular), phaeochromocytoma (metanephrines), thyroid disease, coarctation (femoral pulses, arm-leg pressure), Cushing syndrome, obstructive sleep apnoea and contraceptive use. Her demographic points at the renal artery: computed tomography or magnetic resonance angiography shows the beaded mid and distal right renal artery with a modestly smaller right kidney.
Two management branches follow. First, is intervention worthwhile? Short-duration hypertension favours angioplasty, which in medial fibroplasia has high technical success and meaningful cure or improvement — usually without a stent, because the lesion is compliant webbing rather than calcified plaque. Second, what else needs screening? Fibromuscular dysplasia is a systemic disease of vessels, so cerebrovascular imaging (for carotid-vertebral involvement and aneurysm) is part of the initial evaluation, and smoking — the one modifiable association — is addressed firmly. The failing branch, dissection, is recognised by sudden neck pain, horner syndrome or neurological deficit and treated as an emergency.
Where the exam sets its traps
Beads are misattributed: the string-of-beads appearance belongs to the mid and distal renal and internal carotid arteries in fibromuscular dysplasia, while atherosclerosis claims the origin and proximal segments — reversing the two is the commonest single-mark loss. Second, candidates reach for immunosuppression on hearing "artery disease in a young woman"; the inflammatory markers are normal because this is not vasculitis, and the treatment is mechanical or medical, not immunological. Third, the dissection link is under-known: fibromuscular dysplasia is a leading underlying arteriopathy in spontaneous cervical artery dissection, so a young adult with a painful Horner syndrome or ischaemic event deserves vascular imaging that includes the renal arteries.
Frequently asked questions
Which arteries are most often involved in fibromuscular dysplasia?
The renal arteries first, then the cervical internal carotid and vertebral arteries, with iliac, mesenteric and other beds less commonly affected.
What produces the string-of-beads appearance?
Medial fibroplasia — alternating rings of collagenous fibrosis and areas of medial attenuation causing irregular dilation alternating with web-like stenoses.
How is fibromuscular dysplasia distinguished from atherosclerotic renal artery stenosis?
By patient profile and lesion site: young women with mid-to-distal beading and normal inflammatory markers versus older patients with risk factors and ostial-proximal plaque.
Why is angioplasty preferred without a stent in renal fibromuscular dysplasia?
The compliant fibrous webs respond well to balloon dilatation alone, with stenting reserved for elastic recoil, flow-limiting dissection or residual gradient.
What cerebrovascular risks accompany fibromuscular dysplasia?
Spontaneous carotid or vertebral artery dissection — a cause of stroke and painful Horner syndrome in young adults — and an association with intracranial aneurysm.