• (anal atresia) Congenital absence of the anus, i.e., the opening at the bottom end of the intestinal tract.
  Human Phenotype Ontology (HPO)
  The Human Phenotype Ontology Project, 2025
• (imperforate anus) A congenital birth defect characterized by the absence of a normal anal opening. It may be associated with other congenital abnormalities.
  NCI
  U.S. National Cancer Institute, 2021
• A congenital abnormality characterized by the persistence of the anal membrane, resulting in a thin membrane covering the normal ANAL CANAL. Imperforation is not always complete and is treated by surgery in infancy. This defect is often associated with NEURAL TUBE DEFECTS; MENTAL RETARDATION; and DOWN SYNDROME.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• Anal atresia is an imperforate anus. In anal atresia, the tissue closing the anus may be several centimeters thick or just a thin membrane of skin. In high supralevator lesions (in which the atresia ends above the levator sling), a fistula often extends from the anal pouch to the perineum or the urethra in males and to the vagina, the...
  Merck Manuals
  Merck & Co., Inc., 2025
• Imperforate anus is a birth defect where the opening to the anus is missing or blocked. The anus, also known as the rectum, is the opening at the end of the intestines through which stool (bowel movement) leaves the body. Imperforate anus may end in a pouch, be too narrow (stenotic or atresic), or open into part of the urinary system,...
  NIH Genetic and Rare Diseases
  National Center for Advancing Translational Sciences