It may involve the external or intracranial parts of the vertebral arteries or the carotid artery. If haemorrhage tracks through the adventitia it may rupture into the subarachnoid space. Alternatively, haemorrhage within the wall may occlude the lumen and result in occlusion and infarction. Fibromuscular dysplasia First described in the renal arteries. The pathogenesis is unknown and it involves medium and small-sized arteries.
Some cases are familial.
It results in narrowing of the lumen, alternating with dilatation. It affects any layer of the arterial wall, but usually mainly the media, with hyperplasia of both muscle and fibrous tissue.