This female patient presented with noisy breathing. The PA chest x-ray shows an abnormal superior mediastinum and cardiac contour. There is a curved bulge to the right of trachea and above the right main bronchus. There is the suggestion of a rounded density to the right of the trachea at T4 level. There is what looks like a left aortic knuckle, but it is somewhat superiorly positioned. There is an abnormal sharp angle in the left mediastinal contour, in the region of the main pulmonary artery. The descending aorta shadow is absent on the left below this level, but there is a double shadow on the right. A lateral film (not shown) showed a marked retrotracheal bulge.
A CT chest was performed in the arterial phase. A diagram of the findings may be seen by clicking on the image above. The left common carotid artery arose from the ascending aorta. The aortic arch was to the right of the trachea, and passed posterior to it. The right common carotid and right subclavian arteries arose from the arch in that order. From the posterior arch, the left subclavian artery arose from a large diverticulum (this corresponds to the left “aortic knuckle” seen on the PA film). The descending aorta then crossed to the right again before passing through the diaphragm in the midline.
This appearance may be due to right aortic arch with aberrent left subclavian artery, or to double aortic arch with atresia of the left arch, subtype 3. This case is more likely to be the former, as there was no narrowing of the trachea, and subtype 3 double aortic arch is rare. The anatomic difference between these two anomalies is persistence or not of an atretic segment of the left arch.
Double aortic arch has been classified as type 1 (both arches patent) and type 2 (one arch atretic). The atretic arch is almost invariably the left. Type 2 double arches may be subclassified according to the position of the atresia. Subtype 1 the atretic segment is between ductus arteriosus and descending aorta; subtype 2 it is between left subclavian artery and ductus arteriosus; subtype 3 it is between left common carotid artery and left subclavian artery; and subtype 4 the atresia is between ascending aorta and left common carotid artery. In subtype 3 it is common for the left subclavian artery to arise from a diverticulum. The diverticulum has the same embryologic origin as that originally described by Burckhard Kommerell, and may reasonably be referred to as a Kommerell’s diverticulum.
Double aortic arch is an important vascular ring anomaly, as the arches and atretic ligamentous cords surround and potentially compress the trachea and oesophagus. A clue as to the presence of double arch on barium swallow is the presence of focal oesophageal narrowing in both the AP and transverse directions.
Credit: Dr Ihor KociumbasCredit: Dr Laughlin Dawes