ABSTRACT
Early in development, the communication between the third and fourth aortic arches-the carotid duct-becomes obliterated, and the extracranial carotid system assumes its adult configuration. These primordial vascular changes and cardiogenesis occur in the cephalad region of the embryonic pharynx. Developmental elongation of the fetal neck subsequently leads to descent of the heart into the mediastinum, with elongation of the innominate and carotid arteries. Maldescent of the heart or persistence of embryonic anatomy is felt responsible for subsequent looping and redundancy of the internal carotid artery.[3] Evidence for the congenital origin of the carotid loop is based upon its identification in fetal postmortem examinations. The anomaly is found in approximately 15% of children studied, with the prevalence rising to 25% of adults.[10] Degenerative changes of the arterial wall with secondary elongation are probably responsible for the higher prevalence in aging populations. Others have identified elastic tissue dysplasia of the tunica media of the carotid artery, a finding supportive of the congenital origin of carotid loops and tortuosities.[11,12] The etiologic significance of degenerative changes secondary to arteriosclerosis-with accentuation by chronic arterial hypertension and other hyperdynamic circulatory statesremains speculative.
