Fibromuscular dysplasia (FMD) is a rare segmental disorder of small and medium-sized arteries (Luscher et al. 1987). The patients are of any age, females are affected more than males, and the cause is unknown. It usually affects more than one artery in the same individual and is most common in the renal arteries, causing hypertension. The mid-cervical portion of the ICA is the most commonly affected artery to the brain. Sometimes the vertebral arteries are affected at the level of the first two cervical vertebrae. Intracranial involvement is exceptional (Arunodaya et al. 1997).
Histologically there is fibrosis and thickening of the arterial wall alternating with atrophy, so the typical angiographic appearance is likened to a "string of beads". In rare cases there is concentric tubular narrowing of the affected segments, or sometimes just a ‘web’ at the proximal ICA (Morgenlander and Goldstein 1991).
FMD is associated with intracranial saccular aneurysms and arteriovenous malformations, and can be complicated by aneurysmal bulging of the atrophic segments as well as by dissection. FMD of some arteries to the brain may be found in up to 1 per cent of routine post-mortems, so that any association with cerebral ischaemia or infarction may be no more than coincidence. Occasionally, however, it may indeed be complicated by thrombosis and embolism. The natural history is unknown and treatment with anticoagulants or angioplasty is entirely empirical.