Fibromuscular dysplasia classification
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Fibromuscular dysplasia Microchapters |
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ASA/ACCF/AHA Guideline Recommendations |
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Management of Patients With Fibromuscular Dysplasia of the Extracranial Carotid Arteries |
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American Roentgen Ray Society Images of Fibromuscular dysplasia classification |
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Risk calculators and risk factors for Fibromuscular dysplasia classification |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mohsen Basiri M.D.
Overview
The classification system for fibromuscular dysplasia (FMD) was first according to the arterial layer involved. (intima, media, or adventitia) . However, with use of TPA for treatment and its preference rather than surgery, the obtaining of pathological specimens are restricted.Thus,today, FMD is a disease diagnosed radiographically and histopathological classification has been replaced by an arteriographic findings . Olin JW, Gornik HL, Bacharach JM, et al. Fibromuscular dysplasia: state of the science and critical unanswered questions: a scientific statement from the American Heart Association. Circulation 2014; 129:1048. 20. Lüscher TF, Lie JT, Stanson AW, et al. Arterial fibromuscular dysplasia. Mayo Clin Proc 1987; 62:931 Historically, FMD has been classified histopathologically into categories based on the dominant arterial layer involved (media, intima, or adventitia) and the composition of the arterial lesion (collagen deposition, known as fibroplasia, or, less commonly, hyperplasia of smooth muscle cells).
Classification
Fibromuscular dysplasia may be classified according to angiographic findings or histological characteristics, as below.
Angiografic classification
- Multifocal FMD
- With angiographic appearance of a "string of beads" due to multiple areas of stenosis and dilatation(image; this subtype corresponds pathologically to medial fibroplasia.
- Focal FMD
- This form is less common (image 2), and it has the angiographic appearance of a "circumferential or tubular stenosis" and corresponds pathologically to intimal fibroplasia. Medial hyperplasia and periarterial hyperplasia are histologic types that may also have a focal appearance.
It has been shown that these two different angiographic subtypes of FMD (multifocal and focal) have different phenotypic presentations and natural history [21]. 21. Savard S, Steichen O, Azarine A, et al. Association between 2 angiographic subtypes of renal artery bromuscular dysplasia and clinical characteristics.Circulation 2012; 126:3062. This has led some investigators to question whether FMD is, in fact, a single disease [22]. Olin JW. Is bromuscular dysplasia a single disease? Circulation 2012;126:2925.
Histologic classification
- Medial fibroplasia
- This type of FMD represents the most common dysplastic lesion, accounting for more than 80 percent of fibromuscular lesions [18,19]. Angiographically, medial fibroplasia is characterized by the classic "string of beads" appearance (image 1). This appearance is due to alternating fibromuscular webs and aneurysmal dilatation. In areas of dilatation, the internal elastic lamina is absent, which is possibly the primary defect. Total occlusion is uncommon. [1]
- Intimal fibroplasia (which accounts for approximately 10 percent of FMD) is caused by circumferential or eccentric deposition of collagen in the intima (image 2). The internal elastic lamina may be intact, fragmented, or duplicated, the latter especially in the childhood form. There is no inflammatory or lipid component.
- In perimedial fibroplasia, which occurs predominately in children, large parts of the media (in particular, the outer zone) are replaced by collagen, with irregular thickening of the media. Total occlusion may occur with development of collateral vasculature. "Beading" is present in this type, but the "beads" are less numerous and are smaller than in medial fibroplasia. Aneurysm formation is uncommon.
- Medial hyperplasia, a rare manifestation, is caused by smooth muscle cell hyperplasia without fibrosis.
- Periarterial hyperplasia, also a rare manifestation, is caused by expansion of the fibrous adventitia; collagen extends into the periarterial fat, with accompanying inflammation