During gestation the midgut grows so rapidly that the intraembryonic coelom is too small to accommodate it. So the midgut with its superior mesenteric artery is extruded into the extra-embryonic coelom in the umbilical cord, forming a temporary physiological umbilical hernia. When the midgut returns back to the intraembronic coelom, rotation of the midgut loop takes place through 270° in anticlockwise direction in three stages.

In the first stage [fifth to tenth week] the growth of the right lobe of the liver carries this organ downward and to the right, taking the left umbilical vein [ligamentum teres] with it. This pulls the prearterial segment of the midgut loop down and to the right. So in effect, the midgut loop rotates through 90° in anticlockwise direction.

Figure 4

Figure 4: Rotation of midgut loop [Figures 4, 5, 6 and 7 have been drawn, photographed & edited by the author]

Normally, in the second stage of rotation [at the tenth to eleventh week of gestation] the midgut loop returns to the abdominal cavity from the umbilical cord. The prearterial part, i.e. the small gut, returns first while the superior mesenteric artery is fixed to the umbilicus. Because the space in the abdomen is limited, the returning coils of intestines are pushed to the left underneath the superior mesenteric artery. The last coils of ileum reduce later and carry the superior mesenteric artery with it as it is reduced. The cecum and right colon reduces next and passes anterior to the right of the superior mesenteric artery. The subsequent growth and elongation of colon pushes the cecum into the right iliac fossa.

Figure 5

Figure 5

In the third stage of rotation [eleventh week to shortly after birth] the gut becomes fixed to the posterior abdominal wall. Arrest of development at any stage changes anatomical placement of organs and also narrows the mesenteric base and impairs fixation, leaving the bowel at high risk for volvulus.

Figure 6

Figure 6

Arrest of the first phase leaves the bowel herniated into the umbilical cord, creating omphalocele. Arrest during the second phase may result in nonrotation, incomplete rotation, hyperrotation, or reversed rotation. Moreover, gastroschisis and diaphragmatic hernias and mesocolic paraduodenal hernias also occur during the late second phase of rotation. Failure of the third phase results in a mobile cecum, unattached duodenum, or unattached small bowel mesentery, which makes it vulnerable to cecal volvulus and internal hernias [1].

Nonrotation is the most common rotational abnormality and is due to failure of normal counterclockwise rotation of the prearterial segment of the small gut around the superior mesenteric artery. In nonrotation of midgut loop, the umbilical ring is lax. So the colon and cecum reduce first. The small gut follows and displaces the colon and superior mesenteric artery to the left. So the small gut lies on the right side, the terminal ileum crosses the midline to meet the cecum and enters on its right instead of left side. The colon is confined mainly to the left side of the abdomen. The whole midgut loop may be suspended in the abdominal cavity by an extremely narrow pedicle, the dudenocolic isthmus thus making it vulnerable for volvulus. Bands fixing the cecum to the lateral abdominal wall develop abnormally crossing the duodenum [Ladd’s band] and have potential for duodenal obstruction. In both nonrotation and incomplete rotation, cecal bands may cause obstruction and ischemia before birth, leading to congenital duodenal atresia or stenosis. Therefore, patency of the duodenum should be checked routinely during corrective surgery [2].

Incomplete rotation is the next most common abnormality and involves arrest of rotation at or near 180°. Thus the cecum lies in the right hypochondrium or in the upper abdomen.

Figure 7

Figure 7: Rotational abnormalities.

Reversed rotation results in a 90° clockwise rotation of the gut. The cecum and ascending colon reduce first, so the transverse colon goes behind the superior mesenteric artery and the duodenum comes anterior to the artery. In such cases the superior mesenteric artery may obstruct the transverse colon.

The term malrotation is used to imply irregular and mixed defects of rotation. The true incidence of malrotation is unknown, since many asymptomatic patients fail to present.

Rotational abnormalities are often associated with other congenital abnormalities like congenital abdominal wall defects, polysplenia or asplenia [2]. The surgeon exploring such patients should diligently look for associated congenital abnormalities.

Abnormal rotation with deficient fixation of gut predisposes the patient to volvulus of the ileocecal segment resulting in intestinal obstruction. Sequelae include ischemia, mucosal necrosis, intramural air formation, gram-negative sepsis, perforation, peritonitis, and death. Midgut volvulus can occur at any age though it more commonly presents in the first few weeks of life. Volvulus presents with irritability with bilious vomiting and later on bloody stools and eventually collapse due to intestinal ischemia. Chronic duodenal obstruction due to Ladd’s band may manifest as intermittent vomiting.

Anomalies of intestinal rotation are most often asymptomatic ^{and are often incidental findings in adults. Nonrotation occurs in approximately 1 in 500 live births [3]. Most patients present in emergency with cramping generalized abdominal pain and vomiting. So most cases of nonrotation in adults are detected at emergency laparotomy for intestinal obstruction due to midgut or ileocecal volvulus [4]. Some patients may give prior history of recurrent vague abdominal pain with bilious vomiting suggestive of intermittent small intestinal obstruction or volvulus. Stooling pattern varies and diarrhea is recorded in 16% [5]. In few cases nonrotation has been noted as an accompanying finding at laparotomy for another condition.}

In the acute symptomatic patient, only emergency laparotomy can provide the correct diagnosis and decrease the risk of bowel gangrene. In the chronic situation, barium studies of the upper and lower gastrointestinal tract may reveal findings suggestive of midgut nonrotation or malrotation.

Duodenal obstruction causes gastric and duodenal distension with a prominent duodenal bulb and air-fluid level. This double-bubble is the classic sign on abdominal radiography. There is relative paucity of gas in the lower abdomen. In older patients, the double bubble may be absent in the asymptomatic phase. The diagnosis may be made by upper GI contrast studies in intermittently symptomatic patients. The duodenum may be distended and may have an abnormal shape. The duodenojejunal junction may be on the right and the cecum may be on the left. The duodenum may show a corkscrew effect suggesting partial volvulus. The small intestines may be entirely in the right side of the abdomen. Barium enema may show a displaced cecum with the ileum entering the cecum from the right. Ultrasound and computed tomography scan of the patient's abdomen ^{showing the superior mesenteric vein located on the left of the superior mesenteric artery suggest nonrotation of the intestine but are not sufficiently accurate to confidently exclude malrotation or volvulus. The CT whirl or whirlpool sign portrays the swirling appearance of bowel and mesentery twisted around the superior mesenteric artery axis.}