[Case report of the right-sided aortic arch (N-type): new classification based on macroscopic observations]

We report on a case with unusual origin of the left subclavian artery, so-called N-type found in a 62-year-old Japanese male in 1995. We took the opportunity in proposing for a new classification based on macroscopic observations. In the present observation, the following arteries branched off from the aortic arch in the order of the left common carotid, the right common carotid, the right subclavian and the left subclavian arteries. There was an aortic diverticum between the left subclavian artery and the dissending aorta. The left subclavian artery passed between the esophagus and the thoracic vertebrae. The arterial ligament connected the left pulmonary artery with the aortic diverticulum of the left subclavian artery. According to our observations, the arch of the aorta, descending aorta, aortic diverticulum of the left subclavian artery, arterial ligament and pulmonary artery joined to foam an incomplete vascular ring around the trachea and esophagus. This case can be classified into the N-type according to classifications by Adachi (1928), Williams (1932, 1935) and Nakagawa (1939). This may be the 22nd report in Japan regarding this kind of combined variations. Our classification also includes those by Takemura (1990) and Edwards (1964). An explanation of the new classification is described below and is also shown in Fig. 3. Abbreviations for classification types have been arranged in the order of the relation to the esophagus, the mirror-image subtyping of the Takemura's classification and the location of the arterial ligament. For example, type Na1 (present case) represents the left subclavian artery passing behind the esophagus, mirror-image to the Takemura's G-type, and left arterial ligament.