Atresia
A/an , or birth defect, can result in a malformation such as the absence of a normal body opening or the failure of a structure to be tubular, which is termed atresia.
Atresia is the absence of normal passage or the failure of a structure to be tubular or fully formed. Atresia can occur in any structure of the body. Examples of atresia include imperforate anus, which is the malformation of the hole between the rectum and anus, and choanal atresi, which is the blockage of the back of the nasal passage,usually by abnormal bony or soft tissue.