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Malrotation/Midgut Volvulus

Faulty embryologic gut herniation, rotation and return to the abdomen. Physiologic herniation of the gut through the umbilicus occurs at 6 weeks and is accompanied by a 270 degree counterclockwise rotation of the developing intestine around the superior mesenteric artery (SMA). By 12 weeks, the intestine returns to the abdomen. The normal small bowel mesentery has a broad attachment stretching diagonally from the duodenojejunal junction (Ligament of Treitz) (in the left upper quadrant) to the cecum (in the right lower quadrant). 1 in 500 live births. It is most commonly caused by incomplete rotation (less than 270 degrees of counterclockwise rotation). Other terminology includes: non-rotation (zero degrees of rotation); reverse rotation (clockwise rotation); and malfixation (short narrow mesenteric stalk with abnormal position of the ligament of Treitz). In all cases there is right-sided small bowel and left-sided large bowel, with positioning of the cecum in the right upper quadrant or left abdomen Associated anomalies are seen in approximately 60% 1 2 and include congenital heart disease with heterotaxy (the abnormal position and arrangement of abdominal organs such as spleen, liver, major blood vessels together with right or left-sided isomerism). It is almost always present with diaphragmatic hernia and abdominal wall defects such as omphalocele and gastroschisis.2 3 Other associations include imperforate anus, duodenal atresia, web, stenosis, pre-duodenal portal vein, annular pancreas and biliary atresia Malrotation predisposes to two problems: midgut volvulus and small bowel obstruction. The close proximity of the cecum to the duodenum is associated with a narrow stalk of mesentery about which the gut may twist, resulting in midgut volvulus. Accompanying superior mesenteric vascular compromise (first venous followed by arterial) can lead to life-threatening ischemia of the small bowel and gangrenous necrosis Coiling of the duodenum with the ascending colon will produce complete or partial duodenal obstruction. Abnormal bands of peritoneum, called Ladd bands, are often found connecting the duodenum and cecum anteriorly; these may (rarely) cause duodenal obstruction. Malrotation with midgut volvulus classically presents in the neonate with bilious vomiting and high intestinal obstruction. While most neonates with bilious vomiting will not have midgut volvulus, this diagnosis must be ruled out. Volvulus is a surgical emergency with a mortality rate of at least 15%.2 Malrotation, due to the danger of volvulus, is also treated as an emergency. In about 60% of cases, malrotation presents within the first month of life;1 5 another 20-30% of cases present between one month and one year of age.3 As children grow older, they become less likely to have a distinct, readily identifiable clinical presentation.6 Symptoms and signs range from recurrent abdominal pain and vomiting to failure to thrive. Physical examination often does not contribute to the diagnosis until a complication of malrotation is present Abdominal radiographs are frequently performed in a child with abdominal symptoms. In simple malrotation, the radiographs may appear normal.6 In midgut volvulus the classic finding on radiograph is that of partial duodenal obstruction (dilation of both the stomach and the proximal duodenum, with a small amount of distal bowel gas). Complete obstruction of the duodenum may also be found. Less frequent but more ominous signs are a gasless abdomen, ileus, or distal small bowel obstruction with multiple dilated loops and air-fluid levels.7 A normal abdominal film does not exclude malrotation! An upper GI series is the diagnostic test for malrotation with midgut volvulus, and must be performed unless delay in surgery would further compromise outcome, as in the case of a moribund child.5 8 This is performed with barium, either administered by bottle or through a nasogastric tube. The normal duodenojejunal junction lies to the left of the left-sided spinal pedicle at the level of the duodenal bulb on a true frontal view.5 The duodenal C-sweep courses posteriorly, inferiorly, anteriorly, then superiorly. Findings on Upper GI in malrotation include:2 5 the duodenojejunal junction is displaced downward and to the right on the frontal view abnormal course of duodenum on lateral view abnormal position of jejunum: lying on the right side of the abdomen In malrotation with midgut volvulus, findings also include:9 dilated fluid-filled duodenum proximal small bowel obstruction "corkscrew" pattern: proximal jejunum spiraling downward in the right or mid upper abdomen in midgut volvulus (rare) mural edema, thick folds Malrotation is very rare in the absence of all of these signs. Sensitivity of the UGI is 85-95%,1 10 with a higher specificity (false positives are rare). Although a displaced duodenojejunal junction is a very sensitive indicator of malrotation, this finding can also occur secondary to distended bowel, masses, and splenomegaly.5 Scoliosis makes it difficult to rule out malrotation because the normal bony landmarks are lost. Barium enema, once used to detect an abnormally positioned cecum, is felt to lack sensitivity (15-20% of malrotations are associated with a normally positioned cecum)5 and a high or mobile cecum can be normal in infancy).1 9 Ultrasound and CT may suggest the diagnosis of malrotation but the sensitivity and specificity are low compared to the upper GI series, and therefore an upper GI examination is mandatory to confirm the diagnosis if suspected on CT or ultrasound.11 12 If the SMV lies to the left of, or posterior to the SMA, malrotation is suggested. However, normal vascular positioning - a SMV slightly ventral and to the right of the SMA - can be found in approximately 30% of malrotation cases. The "whirlpool sign" on color Doppler shows mesentery and flow within the superior mesenteric vein (SMV) wrapping around the SMA, indicating malrotation with volvulus.13 14 A dilated, fluid-filled duodenum is frequently seen in cases of obstruction without volvulus. The treatment for malrotation with midgut volvulus is the Ladd procedure: the volvulus is untwisted, and the viable bowel is returned to the abdomen in a completely non-rotated position. Any non-viable bowel is resected and appendectomy is usually performed. No malrotation is "incidental": all cases of malrotation without midgut volvulus or bowel obstruction are treated in the same way due the risk of sudden volvulus. Ladd bands are distinct from the Ladd procedure. Complications of midgut volvulus include short gut syndrome and death.