Atresia

Atresia (plural: atresias) refers to a situation where there is absence, underdevelopment or abnormal closure, of a normal anatomical tubular structure or opening. 

Contrast this with agenesis which refers to the complete absence of any anatomical structure including its primordial precursors.

For example:

• respiratory tract
  • bronchial atresia
  • choanal atresia
  • tracheal atresia
  • laryngeal atresia
• alimentary tract
  • esophageal atresia
  • duodenal atresia
  • ileal atresia
  • jejunal atresia
  • jejunoileal atresia
  • colonic atresia
  • anal atresia
• bile ducts
  • biliary atresia
• genitourinary tract
  • vaginal atresia
    • lower vaginal atresia
  • urethral atresia
• skeleton
  • oval window atresia

Some authors occasionally overlap the two terms (i.e. atresia and agenesis), which in general is an erroneous practice.