Fibromuscular Dysplasia

Fibromuscular dysplasia (FMD) is an idiopathic, non-atherosclerotic, non-inflammatory disease of medium-sized arteries. Abnormal cellular proliferation and disordered arterial architecture weaken or narrow the vessel wall. The renal arteries and extracranial carotid and vertebral arteries are most often involved, although FMD can affect several vascular beds. The angiographic classification is now binary. Multifocal FMD causes alternating areas of stenosis and dilatation—the familiar “string of beads.” Focal FMD produces one concentric or tubular stenosis and may occur anywhere in the affected artery. Older labels such as medial or intimal fibroplasia are histologic descriptions and are no longer the primary clinical classification. A stenotic renal lesion reduces perfusion pressure distal to the narrowing. The kidney interprets that change as inadequate circulating volume, releases renin, and activates the renin–angiotensin–aldosterone system. Angiotensin II raises vascular tone, while aldosterone promotes sodium and water retention. The resulting renovascular hypertension may be the first visible consequence of otherwise silent renal FMD. Cervical disease produces symptoms through turbulent flow, thromboembolism, arterial narrowing, or dissection. Pulsatile tinnitus reflects flow heard near the ear; headache and neck pain are less specific....