Fibromuscular dysplasia (FMDA) is a nonatherosclerotic, noninflammatory arterial disease that most commonly involves the renal and carotid arteries. The prevalence of symptomatic renal artery FMDA is about 4 in 1,000 and the prevalence of cervicocranial FMDA is about half of that. Histologic classification includes 3 main subtypes, intimal, medial, and perimedial, which may be associated in a single patient. Angiographic classification includes the multifocal type, with multiple stenoses and the 'string of beads' appearance that is related to medial FMDA, and tubular and focal types, which are not clearly related to specific histologic lesions (summary by Plouin et al., 2007)

A separation (dissection) of the layers of the internal carotid artery wall.

A small, sac-like aneurysm (outpouching) of a cerebral blood vessel.

A localized circumferential (i.e., bulges on all sides) dilatation or ballooning of a cerebral artery.

Hemorrhage occurring between the arachnoid mater and the pia mater.