A

Fig. 1.6a,b. Midgut volvulus. A 5-day-old neonate with severe vomiting. a Abdominal plain radiograph shows marked distension of the stomach and duodenal bulb and absence of air more distally. b Surgery demonstrated midgut volvulus with necrosis of the entire midgut

obstruct the bowel lumen, but also the lymphatic drainage, the venous drainage, and eventually, the arterial supply. Obstruction of the vascular supply can be a life-threatening condition requiring immediate surgical intervention (SpigLand et al. 1990; Pickhardt and Bhana 2002).

A patient with malrotation may also develop dense peritoneal bands, termed Ladd's bands, that originate in an attempt to fix the bowel. These bands extend from the cecum to the hilum of the liver, posterior peritoneum, or abdominal wall across the duodenum and can cause extrinsic duodenal obstruction.

Volvulus of the midgut may occur at any age but it is more common in the first month of life, most of them presenting in the first week of life (Torres and Ziegler 1993). In general, the symptoms are those of obstruction. The child with obstruction secondary to midgut volvulus typically presents with a sudden onset of bilious vomiting often preceded by initial toleration of feeding. The sudden onset of bilious emesis in a neonate who has been normal for the first few days of life should be considered to be due to a midgut volvulus until proven otherwise (Buonomo 1997). In the early stages, prior to the onset of ischemia, the abdomen is not distended. Patients presenting with shock have a worse prognosis. This manifests as abdominal distension with peritonitis, bloody stools, and hemodynamic comprise (Bonadio et al. 1991).

The imaging work-up begins with a plain radiograph. An anteroposterior supine view and either an upright view or cross-table lateral view should be obtained. In general, the abdominal plain radiograph shows evidence of obstruction, usually in the third portion of the duodenum but occasionally, higher or even lower. The stomach and proximal portion of the duodenum are dilated and some air is usually seen in the jejunum and ileum (Fig. 1.8). These cases are frequently identical in appearance to duodenal stenosis and other incomplete congenital duodenal obstructions. As already noted, complete duodenal obstruction with the double bubble sign may also be a presentation form, this pattern being indistinguishable from other causes of complete congenital duodenal obstruction. The abdominal radiograph may be normal if the obstruction is recent, intermittent, or incomplete, or may demonstrate a relative paucity of bowel air (Kassner and Kottmeier 1975; Frye et al. 1972). The significance of these findings must be recognized in the context of an infant with bilious vomiting, because they are much more alarming than multiple dilated loops of bowel, which denote a more distal obstruction from a cause other than midgut volvulus (Hernanz-Schulman 1999). A gasless abdomen associated with abdominal distension or tenderness may be a sign of strangulated midgut volvulus (Kassner and Kottmeier 1975). Diffuse gaseous distension of the bowel with a "low obstruction" pattern is uncommon and correlates with gangrenous bowel, perhaps because vascular occlusion interferes with resorption of air (Frye et al. 1972) (Fig. 1.9).

An upper gastrointestinal series is the preferred imaging modality for the radiologic diagnosis of a midgut volvulus and should be performed in all patients with bilious emesis, except in those with evidence of complete duodenal obstruction in the plain radiograph or in critically ill infants. A non-ionic, water-soluble contrast medium is preferable, although barium can also be used. Ionic hypertonic solutions, such as gastrographin, are to be avoided a

Fig. 1.8a,b. Midgut volvulus. Supine (a) and lateral (b) radiographs show distension of the stomach and duodenum with some distal intestinal air in a 12-day-old infant with severe vomiting

Fig. 1.8a,b. Midgut volvulus. Supine (a) and lateral (b) radiographs show distension of the stomach and duodenum with some distal intestinal air in a 12-day-old infant with severe vomiting b a

Fig. 1.9a-c. Different patterns of midgut volvulus in plain abdominal radiographs. a Normal air pattern in a neonate with bilious vomiting. b Another neonate patient with bilious vomiting. There are a few dilated bowel loops suggesting high intestinal obstruction. c Obstructed, distended gas pattern suggesting devitalized bowel probably due to venous obstruction and infarction

Fig. 1.9a-c. Different patterns of midgut volvulus in plain abdominal radiographs. a Normal air pattern in a neonate with bilious vomiting. b Another neonate patient with bilious vomiting. There are a few dilated bowel loops suggesting high intestinal obstruction. c Obstructed, distended gas pattern suggesting devitalized bowel probably due to venous obstruction and infarction as aspiration causes pulmonary edema that may be fatal. The contrast medium may be administered orally or, even better, through a nasogastric tube to control the amount of contrast, because a contrast-filled, distended stomach may obscure the course and configuration of the duodenum. The pathogno monic finding of midgut volvulus in the upper gastrointestinal examination is a spiral or "corkscrew appearance" of the twisted distal duodenum and jejunum that are located in the middle of the abdomen (Strouse 2004; Long et al. 1996) (Fig. 1.10). The bowel lumen is narrowed and the duodenum proximal to the obstruction may be mildly dilated. The contrast pass from the stomach to the duodenum and jejunum showing the characteristic corkscrew course both in the anteroposterior and lateral views. In the lateral view the distal duodenum will exhibit a characteristic anterior course (Fig. 1.10) (Koplewitz and Daneman 1999). When there is complete obstruction, the contrast medium cannot enter the volvulized loops to show the "corkscrew" and only the entrance to the volvulus is identified, with a tapered or "beaked" appearance (Fig. 1.11). In cases of recent complete obstruction, distal air may be seen; however, the contrast cannot enter the vol-vulized segment, so the corkscrew image cannot be seen. Once the findings of volvulus are confirmed, no further imaging studies are necessary. Surgical intervention is mandatory immediately following the diagnosis.

Obstruction due to Ladd's bands produces a Z-shaped configuration, outlining the lack of normal rotation and fixation of the duodenum. The Z-con-figuration may appear similar to the "corkscrew" of volvulus, but it does not indicate volvulus itself (Fig. 1.12). It must be stressed, however, that in most children with malrotation obstruction is caused by the volvulus with the band playing a lesser role or no roll at all (Ford et al. 1992; Torres and Ziegler 1993).

Fig. 1.10a-c. Midgut volvulus in a 16-day-old male with bilious vomiting. a Upper gastrointestinal study, anteroposterior projection. Radiograph demonstrates the corkscrew configuration of the duodenum and proximal jejunum. b Lateral projection. The spiral or corkscrew appearance of the duodenum and jejunum is again shown (arrows). The anterior course of the distal duodenum is demonstrated. c Midgut volvulus (arrows) without ischemia was found at surgery

Fig. 1.11a,b. Midgut volvulus in a 7-day-old girl with bilious vomiting. Upper gastrointestinal series. Anteroposterior (a) and lateral projections (b). The distal duodenum courses anteriorly and tapers to a "beaked" obstruction (arrow). No contrast is observed beyond the obstruction, but there is distal air indicating a recent complete obstruction

Fig. 1.11a,b. Midgut volvulus in a 7-day-old girl with bilious vomiting. Upper gastrointestinal series. Anteroposterior (a) and lateral projections (b). The distal duodenum courses anteriorly and tapers to a "beaked" obstruction (arrow). No contrast is observed beyond the obstruction, but there is distal air indicating a recent complete obstruction

Fig. 1.12a,b. Malrotation with z-shape of the duodenum and jejunum. Upper gastrointestinal series. Anteroposterior (a) and lateral (b) projections show a central, downward, Z course of the duodenum. No volvulus was found at surgery. Surgery demonstrated the partial obstruction to be produced by Ladd's bands

Fig. 1.12a,b. Malrotation with z-shape of the duodenum and jejunum. Upper gastrointestinal series. Anteroposterior (a) and lateral (b) projections show a central, downward, Z course of the duodenum. No volvulus was found at surgery. Surgery demonstrated the partial obstruction to be produced by Ladd's bands

Currently, a contrast enema has fallen out of favor for the diagnosis of malrotation and its main complication is that the cecum can be normal in up to 20%-30% of infants with malrotation and, therefore, a normal cecum does not exclude malrotation (Slovis et al. 1980). On the other hand, approximately 15% of patients with normal rotation have a mobile cecum that could be misinterpreted as malfixation (Beasley and De Campo 1987). Nevertheless, demonstration of an unequivocally abnormal cecal position in the setting of an equivocal upper gastrointestinal series may be helpful (Strouse 2004).

Ultrasound may also be a useful tool in the early detection of midgut volvulus because of its availabil ity, relative lack of need for preparation, and lack of ionizing radiation. In fact, several authors currently recommend routine US examination before performing a gastrointestinal series in any patient with bilious vomiting if surgery is going to be delayed, for several reasons: (1) It can be performed at the bedside. (2) It provides information about the outside part of the bowel loops and the abdominal cavity not provided by the contrast examination. (3) In complete obstruction, it provides information about the intestinal loops beyond the obstruction (Babcock 2002; WEiNbERGER et al. 1992).

The characteristic finding of midgut volvulus in the US examination is the "whirlpool" sign produced by the twisting of the bowel, mesentery, and superior mesenteric vein around the axis of the superior mesenteric artery (Fig. 1.13). The whirlpool sign, proposed by PRacROS et al. (1992), directly indicates the anatomic alteration caused by midgut volvulus. The SMV and tributaries wrap around the SMA as a result of the volvulus, resulting in a partial or com plete blockage of the blood supply to the midgut. The whirlpool sign represents this characteristic pattern of the SMV and SMA on sonograms (Chao et al. 2000; Pracros et al. 1992; Shimanuki et al. 1996). Color Doppler reveals a circle of vascularity representing the superior mesenteric vein twisting around the superior mesenteric artery (Patino et al. 2004). Other described findings such as dilated thick-walled bowel loops, mainly to the right of the spine, increased peritoneal fluid, a dilated duodenum, a truncated SMA, and a solitary hyperdynamic pulsating SMA, are also useful findings in a proper clinical setting but are non-specific (Sze et al. 2002; Smet et al. 1991; Chao et al 2000).

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