Atresia: Absence of a normal opening or failure of a structure to be tubular.

Atresia can affect many structures in the body, including: Anal atresia -- congenital absence of a hole at the bottom end of the intestine. Also called imperforate anus. Aortic atresia -- congenital absence of the normal valvular opening into the aorta. Biliary atresia -- absence of the major bile ducts, causing jaundice. Choanal atresia -- congenital failure of one or both nasal passages to open. Esophageal atresia -- a birth defect in which part of esophagus is not hollow. Intestinal atresia -- obliteration of the hollow of the small intestine, involving the ileum (50% of cases) or the jejunum or duodenum. Laryngeal atresia -- congenital failure of the laryngeal opening to develop, resulting in partial or total obstruction at or just above or below the glottis. Pulmonary atresia -- congenital absence of the pulmonary valve opening in the heart. Tricuspid atresia -- congenital lack of the tricuspid valve opening. Vaginal atresia -- congenital occlusion of the vagina or subsequence adhesion (sticking together) of the walls of the vagina occluding it.