Malrotation

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Malrotation refers to abnormal intestinal rotation. Intestinal rotation is a complex embryologic process which is difficult to understand, even for most physicians. The intestines are outside the abdomen during early fetal development, and re-enter the abdomen in a complicated, predetermined sequence. Malrotation occurs when there is an error in one of these stages. The highly variable nature of malrotation is due to multiple different errors occurring at various stages of rotation.

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Detorsion of midgut volvulus
 
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How common is malrotation?
The autopsy prevalence is as high as 0.5 to 1%, but clinically malrotation only presents in 1 per 4000 live births. Males and females are affected equally. Babies are at highest risk of problems, with 50% to 75% of those who become symptomatic doing so in the first month of life and 90% during the first year of life.

Normal Rotation: First Stage (Herniation)

  • Middle portion of growing intestine begins to herniate into the body stalk at 6 weeks
  • As it herniates, it undergoes a 180 degree counterclockwise twist around the SMA
  • The proximal limb elongates faster than the distal limb
  • The colon remains relatively straight

Normal Rotation: Second Stage (Return to the Abdomen)

  • Undergoes a further 90 degree rotation counterclockwise to make the total rotation 270 degrees counterclockwise
  • The “pre-arterial” limb enters first
  • The terminal ileum and cecum last

Normal Rotation: Third Stage (Fixation)

  • Fixation occurs from 12 weeks until after birth
  • Portions of the mesentery fuse with the posterior peritoneum

Abnormal Rotation

  • Stage I (usually occurs normally)
  • Stage II (Classic Malrotation)
  • Stage III (nonrotation, cecal volvulus)

Second Stage Anomalies: Return to the Abdomen

  • Nonrotation
  • Rotates through 90 degrees only, instead of 270 degrees
  • Distal limb (colon) enters first instead of last , colon on the left; small bowel on the right
  • 0.5% of autopsies; twice as frequently in males than females
  • Clockwise volvulus is the main danger

Nonrotation
In nonrotation, the cecum is in the left lower quadrant and the base of the small bowel mesentery is broad and not predisposed to volvulus. These children can be safely observed. While volvulus can occur, surgery does not decrease risk.

Second Stage Anomalies: Return to the Abdomen

  • Malrotation
  • Rotates only 180 degrees, instead of 270 degrees
  • Terminal ileum enter abdomen first
  • Cecum is in a subhepatic location on the right

Second Stage Anomalies: Return to the Abdomen

  • Malrotation
  • Ladd bands (peritoneal bands) attach the cecocolic loop to the posterior abdominal wall

Second Stage Anomalies: Return to the Abdomen

  • Ladd’s bands may compress the second part of the nonrotated duodenum
  • Entire midgut being suspended on the superior mesenteric vessels on a narrow stalk
  • This mesentery is prone to volvulus

Second Stage Anomalies: Return to the Abdomen
2 Other Rare Variants: reversed rotation and hyper-rotation

Reversed rotation

  • In stage 1 the intestine rotates 90 degrees counterclockwise (instead of 180)
  • In stage 2 the intestine rotates 180 degrees clockwise (i.e., the final 180 degrees of rotation is clockwise instead of counterclockwise)

Second Stage Anomalies: Return to the Abdomen

  • Reversed rotation (2 subtypes)
  • If the colon enters first, the colon is posterior to the SMA
  • This can cause obstruction of the transverse colon and is usually presents in adulthood
  • If the small bowel enters first, the small bowel is on the left and anterior to the artery and the colon is on the right
  • Opposite of nonrotation

Second Stage Anomalies: Return to the Abdomen

  • Hyperrotation
  • Rotation continues through 360 or 450 degrees
  • Instead of stopping at 270 degrees
  • Cecum in pelvis or in area of splenic flexure of the colon in the LUQ

Third Stage: Failure of Fixation

  • Normal rotation, but cecum and ascending colon are not fixed
  • Present in as many as 10% of asymptomatic individuals
  • more common in females (mobile cecum)
  • May allow cecal volvulus

Clinical Aspects:

  • Bilious Emesis (95%)
  • Volvulus
  • May present acutely (usually in first year of life) or as chronic intermittent or partial obstruction
  • Duodenal obstruction
  • Internal herniation

Diagnosis is with upper GI series which will show an abnormal position of ligament of Treitz or perhaps duodenal obstruction. Barium enema may show an abnormally placed cecum, but normal placement does not Rule out malrotation. Transverse colon may occasionally show obstruction if volvulus is present.

Volvulus: twisting of the bowel mesentery. This may lead to loss of blood to the intestine, dead intestine, and ultimately death if untreated. Approximately 60% to 80% of neonates with malrotation develop volvulus.

Treatment for malrotation is a Ladd's procedure. The bands obstructing the duodenum are divided if present, and the bowel is placed in position of nonrotation (small intestine on right, large bowel on the left, cecum in the left hypochondrium). Appendectomy (not described by Ladd) is often done at the same operation. No fixation of the bowel is done. Unfortunately, fixation of the intestine only leads to a higher risk of twisting around the fixated points.

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Radiograph of malrotation
 
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