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Malrotation of the Midgut

Malrotation of the Midgut

This disorder occurs in fetal development, when the midgut supplied by the superior mesenteric artery grows too rapidly to be accommodated in the abdominal cavity. Prolapse into the umbilical cord occurs around the sixth week of gestation. Between the tenth and eleventh weeks, the midgut retracts from its location at the exocelomic umbilical stalk back into the abdominal cavity. During this return, the midgut undergoes a 270-degree counterclockwise rotation about the axis of the superior mesenteric artery, followed by fixation to the posterior abdominal wall. Malrotation results from failure of the midgut to properly rotate and affix itself to this wall. This disorder occurs approximately once in 500 live births. The malrotated bowel itself does not cause any significant problem. However, the intestine remains free on a narrow-based mesentery that may twist around itself, producing a midgut volvulus. In addition, dense peritoneal bands (Ladd bands) (A) may extend from the malpositioned cecum across the second part of the duodenum to the liver, posterior peritoneum, or abdominal wall, thereby causing abdominal obstruction. Lack of fixation of the mesentery of the colon and duodenum results in the formation of potential hernial pouches. Internal hernias--the most common of which are right and left mesocolic hernias--can cause entrapment of the bowel. Symptoms resulting from malrotation may occur at any age. Half to three quarters of patients who become symptomatic do so in the first month of life; approximately 90% of patients are symptomatic within the first year. Vomiting--often bilious--is the usual presenting sign. Blood in the stool suggests ischemia and possible gangrene of the bowel. Abdominal distension is usually not remarkable in the initial stage. Once infarction occurs, painful abdominal distension and shock develop. Older children with malrotation may present with recurrent abdominal pain, intermittent vomiting, chronic diarrhea, malabsorption, and failure to thrive. Associated anomalies are found in 30% to 60% of patients with malrotation. These include diaphragmatic hernia, omphalocele, gastroschisis, intestinal atresia, imperforate anus, Meckel diverticulum, mesenteric cyst, Hirschsprung disease, congenital heart disease, and heterotaxia. Plain abdominal radiographs may show a distended stomach and proximal duodenum with a paucity of air in the distal small bowel. Multiple dilated loops of bowel or multiple airfluid levels are usually not seen unless the child has a volvulus complicated by bowel infarction or an internal hernia complicated by intestinal obstruction (B). An upper GI tract series is the study of choice and may help reveal the abnormal position of the duodenojejunal junction and duodenal obstruction. This abnormality has a characteristic "corkscrew," "coiled," or "bird's beak" appearance (C). Early surgical intervention is imperative in a symptomatic patient to minimize the risk of midgut gangrene. Preoperative measures include intravenous hydration to restore fluid and electrolyte balance, nasogastric suction, and intravenous antibiotics (because a bowel resection may be necessary). The procedure of choice--the Ladd procedure--includes evisceration of the midgut and inspection of the mesenteric root, counterclockwise derotation of the volvulus, division of Ladd bands from the cecum across the duodenum, appendectomy, and placement of the cecum in the left lower quadrant. The appendectomy is performed because the cecum is located in an atypical position, which makes a future diagnosis of appendicitis difficult. Nonviable intestinal segments are resected and primary anastomosis is performed. If viability of the bowel remains in question, the abdomen is closed and the patient is given supportive therapy. A second-look procedure is performed at 24 to 36 hours. For the asymptomatic child younger than 2 years, timely repair is indicated because most of the potential complications occur at earlier ages. The management of the older asymptomatic patient is controversial. Some experts believe that corrective surgery should be performed unless compelling contraindications are present.

 
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