EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
88. Congenital Malformations of The Digestive System: Midgut Malformations
Review of MEDICAL EMBRYOLOGY Book by BEN PANSKY, Ph.D, M.D.
- Midgut malformations are common and may result from abnormal development of the digestive tube, incomplete rotation, and/or failure of fixation, from abnormalities in its location and arrangement, or from defective development of neighboring organs. More than one cause may be interconnected. The major clinical manifestation of malformation is a syndrome of neonatal intestinal obstruction
- UNDERDEVELOPMENT
- Agenesis: complete absence of an intestinal segment (incompatible with survival if it is very extensive)
- Atresia and stenosis: an intestinal segment is, and remains, narrow and constricted (obstructs the passage of food)
- Seen most often in the ileum
- Duodenal atresia: distal to the duodenal papilla; vomitus always has bile
- Polyhydramnios may occur with duodenal atresia
- Cause often failure of recanalization or interruption of the blood supply
- Aplasia: where the contracted segment does have a mucosa and lumen
- Mucosal narrowing: often associated with other anomalies
- OVERDEVELOPMENT
- Duplications: range from simple diverticulae to almost complete doubling of the digestive tub Also may include many varieties of cystic malformations
- Commonly found on the dorsal (mesenteric) border of the intestine
- All duplications are caused by failure of normal recanalization and formation of two lumina
- OMPHALOCELE OR EXOMPHALOS: seen in 1/6500 births and results from failure of the intestines to return to the abdomen during stage 2 of midgut loop rotation. The loop remains in the extraembryonic coelom of the umbilical cord
- Hernia can be a single loop of bowel or may contain most of the intestine as well as the spleen, liver, and pancreas
- The hernial sac is covered by the amnion of the umbilical cord
- Eventration of the abdominal viscera or congenital umbilical hernia (type of omphalocele) is due to faulty closure of the lateral body folds during week 4 of embryonic lif The abdominal viscera develop outside the embryo in a sac of amnion.
- Is often associated with exstrophy of the urinary bladder
- Gastroschisis is uncommon; due to a defect of the anterior abdominal wall (not stomach) with extrusion of abdominal contents without involving umbilical cord
- The viscera protrude into the amniotic sac and float in fluid
- Usually seen on the right side and is more common in males
- ANOMALIES OF POSITION
- Nonrotation: quite common; called "left-sided colon" and generally is asymptomatic, but twisting or volvulus can occur
- Midgut does not rotate after it enters the abdomen. Thus, the caudal limb enters before the cranial limb
- Small intestines lie on the right side and the entire large intestines on left. May cause obstruction of vessels and gut if kinking or twisting occurs
- Volvulus and mixed rotation: cecum lies below the pyloris and is fixed to the posterior abdominal wall by peritoneal bands that cross over the duodenum
- Usually causes duodenal obstruction
- Due to a failure of the midgut loop to complete final 90 degrees of rotation, thus, terminal ileum enters the abdominal cavity first
- Reversed rotation: rare, clockwise rotation (not counterclockwise)
- Duodenum lies in front of the superior mesenteric artery and transverse colon behind it, which may obstruct the latter due to pressure from the artery
- Small intestines lie on the left; large intestines lie on the right, and cecum is found in the center
