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.