Fibromuscular Dysplasia

Fibromuscular dysplasia (FMD) is an idiopathic, segmental, non-atherosclerotic, non-inflammatory disease of the arterial wall that causes stenosis in small- and medium-sized arteries. The renal arteries and extracranial carotid and vertebral arteries are commonly involved, although FMD can affect several vascular beds. Its cause remains uncertain and probably reflects genetic and environmental factors. The angiographic classification is binary. Multifocal FMD causes alternating areas of stenosis and dilatation—the familiar "string of beads"—and usually affects the mid-to-distal artery. Focal FMD produces one concentric or tubular stenosis and may occur anywhere in the artery. Older histologic labels are no longer the primary clinical classification. A stenotic renal lesion lowers perfusion pressure beyond the narrowing. The kidney responds with renin release and activation of the renin–angiotensin–aldosterone system. Angiotensin II raises vascular tone, while aldosterone promotes sodium and water retention; renovascular hypertension may therefore be the first sign of renal FMD. Cervical disease may cause turbulent flow, thromboembolism, narrowing, or dissection. Pulsatile tinnitus reflects flow heard near the ear; headache and neck pain are less specific. A transient ischemic attack (TIA) or stroke indicates cerebral ischemia,...