Fibromuscular Dysplasia: Renal and Carotid Involvement

Fibromuscular dysplasia (FMD) is a non-atherosclerotic, non-inflammatory vascular disease characterized by abnormal cell growth in the arterial wall leading to stenosis, aneurysm, or dissection. The most common subtype is medial fibroplasia, accounting for 80-90% of cases, which produces the classic 'string of beads' appearance on angiography due to alternating areas of stenosis and mural aneurysms in the arterial media. The pathogenesis involves dysregulation of smooth muscle cell proliferation, collagen deposition, and elastic fiber destruction within the arterial wall layers. Renal artery FMD activates the renin-angiotensin-aldosterone system through reduced renal perfusion pressure, causing secondary renovascular hypertension — characteristically presenting in young women (20-50 years) with resistant hypertension. Carotid and vertebral FMD can cause cerebrovascular symptoms including TIA, stroke, or dissection. Unlike atherosclerosis, FMD affects the mid and distal segments of arteries, occurs predominantly in women (9:1 female-to-male ratio), and is not associated with traditional cardiovascular risk factors.