Embryology and anomalies of the external ear.

Malformations of the auricle are not uncommon and occur in 1 out of 12500 births. They can occur alone or can be associated with genetically determined syndromes. Most congenital malformations in the human occur during the third to twelfth weeks of embryonic life. During this period, the external ear is undergoing development and can be affected in many ways. There are three parts to the external ear: the auricle, the cartilaginous external auditory canal, and the bony external canal. The auricle (pinna) and the cartilaginous canal are closely related and probably develop from the same anlage. The bony canal is derived from the tympanic ring which is an incomplete cylinder of membranous bone. It must be clearly understood that, although this article is primarily concerned with the morphogenesis and dysmorphogenesis of the auricle, the rest of the external ear, specifically the external auditory canal, is developing simultaneously. Therefore, maldevelopment of the external canal and the auricle will frequently occur together.