3D coloured computed tomography (CT) scan of the heart of a patient with Kommerell diverticulum, a rare congenital (present from birth) anomaly of the aortic arch (upper centre left). The aorta is the main artery that carries blood from the heart to the rest of the body. A diverticulum is a bulging pouch. Kommerell diverticulum may be asymptomatic or cause symptoms due to the compression of surrounding structures such as the trachea (wind pipe) or oesophagus (gullet). A possible complication is rupture of the diverticulum, which can be fatal. Therefore, surgical intervention to repair or replace the aortic arch is necessary.