Congenital Intestinal Defects
Midgut malformations
- Rotation defects
- Omphalocele
- Meckel's diverticulum
Recall that, typically, the primary intestinal loop undergoes 270 degrees counterclockwise rotation as it elongates; in the final position, the large intestine "frames" the small intestine.
Rotation Defects
- Non-rotation
- When rotation does not occur, the small intestine lies to the right of the large intestine (thus, it this defect is sometimes referred to as "left-sided colon").
- Reversed rotation
- When rotation occurs clockwise; in this case, the duodenum will pass ventral to the transverse colon, instead of dorsal to it.
- Mixed rotation
- When rotation of the cranial and caudal intestinal segments is not coordinated: only the cranial end undergoes the first rotation, and only the caudal end undergoes the second. The cecum lies at the midline, just inferior to the pyloric region of
- Occurs when the abdominal viscera protrude through the umbilical ring
- The viscera is covered in a vascular membrane, which is susceptible to rupture (not to be confused with gastroschisis, in which the viscera protrude from the anterior body wall but are not covered by a membrane).
- Omphalocele is often present in conjunction with other abnormalities, and is thought to occur as result of failure to fully retract during midgut rotation, lateral body folding failures, or failure of connective tissues in the abdominal wall.
- Present when the vitelline duct fails to fully regress.
- Its location and length are variable, and, in many cases, is asymptomatic. However, if the diverticulum contains pancreatic or gastric tissues, bleeding ulcers can form.
Hindgut Malformations
- Fistulas
- Imperforate anus
- Rectourethral fistulas occur when the urinary and digestive tracts are connected.
- Thus, both urine and feces are directed through the urethra, and surgery is required.
- Rectovaginal fistulas are characterized by a connection between the vagina and rectum.
- The connection between the rectum and vagina channels rectal contents to the vagina; surgery is required to form a separate outlet for feces.
Presents in various permutations; corrective surgeries are necessary to treat imperforate anus, which is often accompanied by fistula.
Agenesis
- Characterized by the formation of a blindly ending anorectal canal.
- Occurs when the anal membrane is abnormally thick, and prevents the anus from opening to the external environment.