ISCHEMIC STROKE / CLASSIFICATION AND ETIOPATHOGENESIS / NONINFALAMMATORY VASCULOPATHIES
Fibromuscular dysplasia (FMD)
Created 14/03/2022, last revision 23/01/2023
- mostly sporadic, rarely hereditary, non-inflammatory disease of unknown etiology affecting medium-sized arteries
- localization (usually sparing the origin of the vessel):
- an extracranial portion of ICA / vertebral arteries
- renal arteries (most common)
- splanchnic arteries (rare)
- subclavian, axillary and iliac arteries (rare)
- usually occurs in young to middle-aged women
- female to male ratio of 3:1
- onset typically between 30-50 years of age
- involved arteries show segmental stenoses and enlargements; ~ 1/3 of patients have multiple lesions
- FMD may lead to serious complications – TIA/stroke, spontaneous dissection, aneurysm formation
Pathology
Pathology- unknown etiology
- identification of YY1AP1 mutations (typical for Grange syndrome) as a cause of FMD indicates that this condition may result from various genetic disorders (Guo, 2017)
- fibrous or fibromuscular thickening of the arterial wall (intima, media, and adventitia) leading to segmental stenoses and microaneurysms
- intima is involved in < 5% of cases (⇒ intimal fibroplasia, also called carotid web)
- media involvement (dominant – 90-95% of cases)
- adventitia (rare, < 1%)
- histology
- accumulations of dysplastic muscle cells + disruption of the internal elastic membrane
- no inflammatory cells are present
- carotid lesions are typically localized in the middle and distal segments of the extracranial internal carotid artery, not rarely extending to the skull base
- FMD predisposes to the development of aneurysms (extra- and intracranial) and arterial dissections
- ⇒ it is advisable, to examine the renal arteries in all patients with dissection
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Clinical presentation and diagnostic evaluation
- carotid artery lesions are often asymptomatic but can cause TIA/stroke
- due to distal thromboembolism (e.g., from the aneurysm)
- due to the dissection
- renal artery involvement leads to renovascular hypertension (by activating RAAS) or renal impairment
- coronary artery involvement can lead to angina pectoris, myocardial infarction, and cardiac death
- FMD is diagnosed by a typical appearance on vascular imaging (CTA, MRA, DSA, ultrasound)
- involved arteries usually have a rosary-like appearance, caused by concentric luminal narrowing alternating with areas of mural dilatation (a string of beads appearance)
- this finding is present in up to 90% of patients with FMD
- less commonly, concentric long-segment tubular stenosis is present
- involved arteries usually have a rosary-like appearance, caused by concentric luminal narrowing alternating with areas of mural dilatation (a string of beads appearance)
- FMD may present with carotid dissection (best seen on fat-saturated T1 imaging)
- less typical features include intracranial aneurysms that can cause subarachnoid hemorrhage (SAH)
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Differential diagnosis
- atherosclerosis – usually appears at the origin or proximal portion of the ICA
- vasculitis
- elevated ESR
- extensive or diffuse thickening of the wall (Takayasu)
- segmental arterial mediolysis (Chao, 2009)
- vasospasms
Management
Stroke prevention
- asymptomatic carotid lesions – most commonly conservative approach is preferred; antiplatelet therapy is not recommended
- stroke patients with FMD:
- strict control of blood pressure and other vascular risk factors
- antiplatelet therapy (AHA/ASA 2021 I/C-LD)
- ASA is most commonly used (based on expert opinion, no studies available)
- statins are not routinely used in FMD unless otherwise indicated
- for stroke caused by carotid dissection without thrombosis, antiplatelet therapy is usually used (AHA/ASA 2021 2a/C-EO)
- if medical treatment fails or significant carotid artery stenosis develops, consider angioplasty (AHA/ASA 2021 2b/C-LD) (Tekieli, 2015)
- angioplasty in FMD has high long-term patency rates; the stent is not always required
- robust data on the clinical benefit of CAS over conservative therapy are lacking
Renovascular hypertension
- angioplasty with stenting of the renal artery is indicated in proven renovascular hypertension
- RAA system provides adequate glomerular pressure by vasoconstriction
- ACE inhibitors may cause renal hypoperfusion
