89. Midgut Malformations

  1. Midgut malformations (continued)
    1. ANOMALIES OF POSITION (continued)
      1. Subhepatic cecum: failure of the proximal colon to elongate during stage 3 of rotation, thus, cecum ends up near the liver
      2. Mobile cecum: due to incomplete fixation of the ascending colon. Results also in a mobile and variable appendix and even volvulus of the cecum
      3. Midgut volvulus: mesenteries fail to undergo normal fixation, and the intestines twist with incomplete rotation of the midgut loop
        1. The small intestines hang by a narrow stalk of the superior mesenteric vessels and twist around it, thus obstructing at or near the duodenojejunal junction
    2. REMNANTS OF THE VITELLINE DUCT: the duct usually disappears at 6 weeks
      1. Meckel's diverticulum is an ileal diverticulum and the most common malformation of the digestive tract (2-4% of people). It is clinically significant because it can become inflamed and cause symptoms mimicking appendicitis
        1. It is located about 2 to 3 feet (0.6-0 m) from the ileocecal valve and is a fingerlike pouch about 3 to 6 cm long arising from the antimesenteric border of the ileum
        2. Its walls contain all the layers of the ileum, but may also contain gastric and pancreatic tissu The gastric mucosa may secrete acid and produce ulceration, bleeding, and perforation
      2. Umbilical or vitelline fistula: vitelline duct remains patent over its entire length, thus, connects the umbilicus and intestinal tract. It may lead to fecal discharge at the umbilicus or ileal prolapse through the fistula
        1. One may find the duct closed at both ends and the formation of a vitelline cyst or enterocystoma in its midportion
      1. Congenital aganglionic dystony or megacolon (Hirschsprung's disease) is rare; may affect the colon, small intestine, or duodenum, but especially the rectum and its internal and external sphincters
        1. Causes a portion of the colon to dilate due to the absence of ganglion cells of the myenteric plexus distal to the dilated segment, as a result of failure of migration of the neural crest cells. The dilated portion itself has a normal population of ganglion cells
        2. Dilatation is caused by failure of the distal segment to move the intestinal contents onward
        3. The severity of the condition is directly proportional to the length of the gut segment involved
      2. Mucoviscidosis: adherence of meconium to the intestinal wall secondary to a deficiency of trypsin secretion by the pancreas as a result of the latter being invaded by interstitial fibrosis of unknown origin

midgut malformations: image #1