ABSTRACT
Most cases of midgut volvulus occur during the neonatal period (1,4), and the usual history is an infant with acute onset of bilious emesis and abdominal distension. Malrotation and midgut volvulus are typically evaluated using contrast radiography. Ultrasonography of the relative positions of the most cranial aspects of
the superior mesenteric artery (SMA) and superior mesenteric vein (SMV) may be useful in more atypical cases. The SMV normally lies to the right of the SMA on axial images (Fig. 2) (5,6). If the SMV is to the left of the left lateral margin of the SMA (Fig. 3), then there is a high chance of malrotation, and further evaluation is warranted (7,8). If the SMV is directly ventral to the SMA, about one-quarter will have malrotation (6,7). However, the literature clearly and repeatedly reports that a normal orientation of the SMV and SMA does not exclude the diagnosis of malrotation (6,8,9). Findings suggestive of midgut volvulus include a clockwise whirlpool sign (10-12), best seen with color Doppler, due to the mesentery wrapping around the SMA, duodenal dilatation with distal tapering (13), fixed midline
FIGURE 1 ■ Bowel layers. Infant with pyloric stenosis and a posteriorly placed pylorus behind the stomach antrum. All five layers of the bowel wall are seen: 1-(echogenic) superficial mucosa, 2-(hypoechoic) deeper superficial mucosa, 3-(echogenic) submucosa, 4-(hypoechoic) muscularis propria, and 5-(echogenic) serosa.
