Cervical aortic arch: a commentary.

C ERVICAL AORTIC ARCH (CAA) was first described by Reid in 1914.’ Rare as it is, CAA provides a link in the embryogenesis of the great arteries of the thorax. Its interesting variations offer a clarifying dimension to the complex confusion of anomalies of the thoracic aorta. The high location of the CAA is usually attributed to persistence of the right or left third arch instead of the fourth arch, thereby rerouting the aorta via the neck. However, failure of the normal caudal migration of the fully developed fourth arch in the growing embryo from the occipital level in the thoracic cage at the seventh week of gestation has also been invoked as a cause of cervical ectopy of the aortic arch.* D’Cruz et al considered CAA to be the result of a confluence of the third and fourth arches as a result of anomalous growth of the pharyngeal pouch tissue, along with failure of the normal fourth arch to descend into the thorax with the heart.3 A good reason to separate CAA from the other forms of anomalous aortic arch is that its unusual connections confirm some of the views that have been expressed as being responsible for the maldevelopment of aortic arch (Felson, Letter from the Editor, p 69). For example, the separate