A Tale of Two Arches

When the pharyngeal arches appear during the 4 th and 5 th weeks of development they receive an artery known as an aortic arch. These aortic arches appear, become modified or regress in a cranial to caudal direction to result in the normal arrangement of an aortic arch with a brachiocephalic trunk, left common carotid and left subclavian arteries. On occasion different patterns of the aortic arches may arise. This paper describes the occurrence of two aortic arch variations found during a routine dissection in a human anatomy course. Aortic arch 1: Left vertebral artery arises directly from arch Four major branches can be observed originating from the aortic arch in this individual. The initial branch is the brachiocephalic trunk, which contains right common carotid and right subclavian arterial branches. The left common carotid artery arises subsequent to the brachiocephalic trunk. Contrary to the typical pattern, the left vertebral artery arises next directly from the aortic arch and traverses posteriorly toward the cervical transverse foramina. The final branch originating from the aortic arch is the left subclavian artery. This variation was described by Thomson1 in 1893 and reported to have occurred in 27 of 500 cases. Aortic arch 2: Right subclavian artery traverses posterior to trachea and esophagus Again, four branches can be observed originating from the aortic arch. The first branch, however, is not the brachiocephalic trunk and instead the right common carotid artery originates directly from the aortic arch. The next branch is the left common carotid artery followed by the left subclavian artery. The right subclavian artery originates after the left subclavian artery and traverses posterior to the trachea and esophagus towards the right clavicle. As the right subclavian artery passes posterior to the esophagus, the right vertebral artery originates. An additional contribution to the right vertebral artery arises from the right common carotid artery. The two vertebral artery contributions join and a single vertebral artery can be seen diving posterior toward the cervical transverse foramina. This aortic arch variation was found to occur in 4 of 500 individuals1. Anatomy courses vary with respect to giving the cause of death of the cadaver prior to dissection. Some courses give the students an opportunity to attempt to determine the cause of death based upon what is identified during the dissection process. Unfortunately, the stated cause of death rarely tells a complete story as numerous “abnormalities” or variations can exist in a body that do not relate to the cause of death. It is uncertain that the aortic arch variations contributed to the cause of death in these two cases and quite possible that they had little impact on the general health of the individuals.