- congenital megacolon
* * *megacolon in a section of the colon due to congenital absence of intrinsic ganglion cells in the myenteric and submucosal plexuses of the next distal segment; the aganglionic part is abnormally narrow, and its loss of motor function causes massive hypertrophic dilatation of more proximal segments. The condition appears soon after birth, is more common in males, and causes extreme constipation, abdominal distention, and sometimes vomiting; when severe, it may result in growth retardation. It is sometimes divided into short-segment and long-segment forms, may occur as an isolated trait or in conjunction with other congenital anomalies, and may show dominant, recessive, or multigenic patterns of inheritance, with gender-dependent penetrance. It has been associated with mutations in one or a combination of several genes, including genes encoding either a protein-tyrosine kinase receptor (RET) or one of its ligands, and genes encoding either endothelin-3 (EDN3) or its receptor (EDNRB). Called also Hirschsprung disease, aganglionic m., and pelvirectal achalasia.
Congenital megacolon; lateral view of barium enema in a three-year-old girl.
Medical dictionary. 2011.