The aortic arch is the curved portion of the aorta connecting the ascending aorta to the descending thoracic aorta, arching superiorly and to the left over the left pulmonary hilum at approximately the level of T4. Three major branches arise from its superior convexity: the brachiocephalic trunk (right), the left common carotid artery, and the left subclavian artery. The ligamentum arteriosum connects the inferior surface of the arch to the left pulmonary artery at the isthmus.
The aortic arch isthmus, just distal to the left subclavian origin at the ligamentum arteriosum attachment, is the most common site of traumatic aortic injury in deceleration trauma. Coarctation of the aorta most commonly occurs at the isthmus, producing upper limb hypertension, rib notching from intercostal collateral enlargement, and a 3 sign on chest radiograph. The arch is accessed during total arch replacement for aneurysmal disease using hypothermic circulatory arrest. The left recurrent laryngeal nerve loops under the arch at the ligamentum arteriosum.
Sudden deceleration in motor vehicle accidents shears the aorta at the fixed isthmus near the ligamentum arteriosum, producing a contained haematoma visible on CT as a mediastinal haematoma with aortic irregularity, managed urgently with endovascular stent grafting or open repair.
Congenital narrowing at the aortic isthmus produces proximal hypertension, diminished femoral pulses, rib notching from collateral intercostal arteries, and left ventricular hypertrophy, treated by balloon angioplasty with stenting or surgical resection and anastomosis.
