Fibromuscular dysplasia (FMD) is an arterial disease characterized by nonatherosclerotic, noninflammatory thickening of the arterial wall, resulting in stenosis, occlusion, aneurysm, or dissection. Most commonly the renal artery (75%-80% of cases), internal carotid artery, and/or and vertebral artery (75% of cases) is affected, but pathologic changes can be found in nearly every arterial bed. Among adults, there is a strong female predominance. Children with FMD do not have female predominance.

Presentation varies significantly and correlates with affected arterial beds. Aneurysms, dissection, occlusion, and thrombosis of affected arteries can occur. The most common sign of FMD is renovascular hypertension due to an affected renal artery; this is especially true in children.

Other signs include stroke, transient ischemic attack, myocardial infarction, and bruits on examination. The most serious presentations are stroke due to cervical artery dissection, myocardial infarction due to spontaneous coronary artery dissection, and subarachnoid or intra-abdominal hemorrhage due to ruptured aneurysm.

Clinical manifestations include pulsatile tinnitus, dizziness, headache, neck pain, neurological dysfunction, chest pain, flank pain, and abdominal pain.

There are two subtypes of FMD based on arterial angiography:

• Multifocal FMD is more common in adults and is defined as at least two areas of stenosis in a vessel segment, which appears as a string of beads. Histologically, this is caused by disorganized collagen in the medial layer of the vessel wall.
• Unifocal FMD presents with a solitary or tubular stenosis caused by intimal or adventitial fibroplasia.