not a true diverticulum, but a bulblike swelling at the origin of the left subclavian artery due to a remnant of the left fourth aortic arch; associated vascular ring compression syndromes involve persistent right aortic arch; the left subclavian artery may pass behind the esophagus; the diverticulum may be large enough to compress the trachea and esophagus even after the vascular ring has been divided and may need to be resected or affixed to the thoracic wall or vertebral fascia.
