The wall of this intramyocardial coronary artery is thickened and the lumen is narrowed due to abundant deranged muscle and fibrous tissue.
Fibromuscular dysplasia was first described in 1938. It is usually manifested as a disease of renal or craniocervical arteries but can involve arteries in almost any location. It may involve coronary arteries without evidence of vascular involvement elsewhere. It has been reported as either an isolated phenomenon or in association with such entities as Noonan syndrome, hypertrophic cardiomyopathy, Friedreich ataxia, scleroderma, and Marfan syndrome. Though most reports are of disease in the larger epicardial coronary arteries, sometimes small epicardial arteries are the site of disease. There have been reports of involvement of the SA node artery and the AV node artery associated with sudden cardiac death. In one series of 1000 cases of sudden cardiac death there were 9 cases of hypertension with fibromuscular disease of small coronary arteries. Though most often reported as involving the epicardial coronary arteries where it can be associated with dissection, it has been reported in cases of sudden death in which the arterial involvement was confined to intramyocardial coronary arteries as in this case. In this case and other reported cases localized fibrosis is seen in the vicinity of the involved vessel.