Kommerell diverticulum (KD) is a developmental anomaly of the aortic arch characterized by a diverticulum at the proximal descending aorta of left or right arch configuration that gives rise to an aberrant subclavian artery. KD is primarily asymptomatic but may become symptomatic secondary to dilatation of KD, atheroma and fibrotic changes in paratracheal or paraesophageal tissue, presenting with signs of tracheal compression (more common in children), esophageal compression (dysphagia lusoria; more common in patients with a right sided aortic arch), chest pain, or blood pressure difference in the upper limbs. KD may also predispose toward aortic dissection or rupture.

Aortic dilatation refers to a dimension that is greater than the 95th percentile for the normal person age, sex and body size. In contrast, an aneurysm is defined as a localized dilation of the aorta that is more than 150 percent of predicted (ratio of observed to expected diameter 1.5 or more). Aneurysm should be distinguished from ectasia, which represents a diffuse dilation of the aorta less than 50 percent of normal aorta diameter.