Malrotation

Embryology

The development of the midgut begins with the differentiation of the primitive intestinal tract into the foregut, midgut, and hindgut at the fourth week of gestation. The mature alimentary tract and all associated digestive organs are formed from this primitive tube. The most accepted model of midgut maturation involves four distinct stages: (1) herniation, (2) rotation, (3) retraction, and (4) fixation. Normal fixation of the duodenum and colon is illustrated in Fig. 31.1 . The intestinal loop can be divided into the cephalic (duodenojejunal) limb and the caudal (cecocolic) limb, which rotate separately but in parallel. The SMA serves as the fulcrum with the omphalomesenteric duct at the apex. Due to the disproportional growth and elongation of the midgut during the fourth gestational week, the intestinal loop herniates into the extraembryonic coelom. Next, the bowel enters a critical period of rotation when the prearterial and postarterial limbs make three separate 90° turns, all in the counterclockwise direction around the SMA. The first 90° rotation occurs outside the abdomen. The second 90° turn commences during the return of the intestine into the abdominal cavity during the 10th gestational week. The duodenojejunal junction now passes posterior to the SMA. The last rotation occurs in the abdomen. The primitive intestine has thus completed a 270° counterclockwise rotation, allowing the duodenojejunal limb to be positioned to the left of the SMA while the cecocolic limb is on the right. Fixation of the ascending and descending colon then occurs. Disruption of any of these vital steps leads to the spectrum of malrotation encountered clinically.

The most common forms of rotational disorders include nonrotation ( Fig. 31.2 ), incomplete rotation ( Fig. 31.3 ), and reversed rotation. Right and left mesocolic hernias can also occur. In nonrotation, there is failure of the normal intestinal 270° counterclockwise rotation around the SMA. Thus, the duodenojejunal limb lies in the right hemi-abdomen with the cecocolic limb in the left hemi-abdomen. Midgut volvulus due to a narrow mesenteric pedicle and extrinsic duodenal obstruction secondary to abnormally positioned cecal attachments are the most common symptomatic consequences. In cases of incomplete rotation, normal rotation has been arrested at or near 180°. The cecum will usually reside in the right upper abdomen. Obstructing peritoneal bands over the duodenum are present. With reversed rotation, an errant 90° clockwise rotation occurs, which leaves a tortuous transverse colon to the right of the SMA, passing through a retroduodenal tunnel dorsal to the artery and in the small bowel mesentery. The duodenum will assume an anterior position. Reverse rotation with volvulus may occur with obstruction of the transverse colon due to trapping of the transverse colon posterior to the anterior duodenum. Paraduodenal hernias are rare and result from failure of the right or left mesocolon to fuse to the posterior body wall. A potential space is created. Subsequently, the small intestine may become sequestered and potentially obstructed.

Presentation

The incidence of malrotation has been estimated at 1 in 6000 live births. An increased incidence of 0.2% has been found in barium swallow studies, whereas autopsy studies estimate that the true incidence may be as high as 1% of the total population. Associated anomalies are common ( Table 31.1 ).

Classic malrotation with midgut volvulus often develops in a previously healthy term neonate. Up to 75% of patients present during the first month of life, while another 15% will present within the first year. However, volvulus and mortality have been reported at all ages. Sudden onset of bilious vomiting is the cardinal sign of neonatal intestinal obstruction, and malrotation with volvulus must be the presumed diagnosis until proven otherwise. Physical examination findings will vary. Initially, the patient may have a scaphoid abdomen or only mild upper abdominal distension. However, if vascular compromise to the completely obstructed bowel develops, the abdomen will become progressively more distended and peritonitis will ensue. Late signs include abdominal wall erythema and shock. Similarly, laboratory data are often nonspecific and of limited diagnostic value. Thus, the clinician must have a high index of suspicion in a previously healthy baby who presents with bilious emesis. Furthermore, if signs of bowel ischemia are present, operative intervention should follow without delay.

Patients with chronic obstruction will present less dramatically. Nonspecific presenting problems such as failure to thrive, gastroesophageal reflux, early satiety, and mild abdominal discomfort are often seen. Partial volvulus can lead to mesenteric venous and lymphatic obstruction, and subsequently impaired nutrient absorption. The diagnosis becomes even more challenging with the older child or teenager because the symptoms are often vague and may sometimes seem unrelated to the abdominal cavity.

Diagnosis

Radiologic studies play a critical role in establishing a diagnosis of intestinal malrotation. The prenatal diagnosis of isolated rotational abnormality is very uncommon, but fetal ultrasonography (US) may show the sequelae of prenatal midgut volvulus, such as bowel dilatation, meconium peritonitis, and/or fetal ascites. Initial evaluation will usually begin with a plain anteroposterior abdominal film combined with a lateral decubitus or upright view ( Fig. 31.4 ). Nonspecific findings ranging from gastric distention to a gasless abdomen are common. The upper gastrointestinal (UGI) contrast study remains the gold standard and is needed to document the position of the ligament of Treitz to the left of the spinal pedicles, and rising to the level of the gastric outlet. Additionally, the lateral film will show the duodenum in a retroperitoneal, posterior position. Findings of abnormal rotation include a low-lying ligament of Treitz or failure of the ligament of Treitz to be located left of the spine. If volvulus has developed, the contrast study may show the “coil spring” or “corkscrew” configuration with incomplete obstruction and the “beak” appearance in the duodenum with complete obstruction ( Figs. 31.5 and 31.6 ). In patients with an enlarged stomach, the ligament of Treitz may become displaced inferiorly, so gastric decompression may be needed during the UGI study.

In some institutions, US is being trialed to make the diagnosis of malrotation, but the sensitivity and specificity are not sufficient to replace UGI for definitive diagnosis. Color Doppler US imaging may reveal a dilated duodenum with inversion of the SMA and vein (the whirlpool sign) in cases of acute volvulus. In children with peritonitis who are too unstable to undergo an UGI study, and midgut volvulus is part of the differential diagnosis, a normal SMA and vein orientation plus absence of a whirlpool sign on US may provide reassurance that the diagnosis is not midgut volvulus. Additionally, Yousefzadeh and colleagues have proposed that US can be used to diagnose malrotation without volvulus based on the position of the duodenum and the SMA. Because the third portion of the duodenum assumes a retroperitoneal position anterior to the aorta and posterior to the SMA in individuals with normal intestinal rotation, verification of this position by US potentially obviates the need for further imaging. This group prospectively validated this technique in 33 neonates at their institution. Zhou et al. reported on 70 patients who were evaluated for malrotation and compared US, UGI, and operative findings. A combination of three sonographic features including inversion of the SMA and vein, the whirlpool sign, and an intraperitoneal transverse duodenum had a sensitivity and specificity of 100% and 98% compared to UGI, which was 40% and 64%, respectively. However, application of this approach prospectively in multiple institutions is likely needed prior to widespread acceptance.

Management