Vomiting of infancy is a common indication for upper GI examination. In this context, the main questions to be answered are: (1) Is there gastric outlet obstruction?
(2) Is the ligament of Treitz normally located? Proto- typic entities under consideration are hypertrophic pyloric stenosis and midgut volvulus.
Midgut malrotation is suspected when the liga- ment of Treitz is abnormally placed. The ligament of Treitz is the point where the retroperitoneal duodenum reenters the peritoneal cavity and forms the proximal retroperitoneal attachment of the mesenteric root. On upper GI, the ligament of Treitz should be on the left side of the vertebral column and at or above the level of the duodenal bulb (Figure 9–7).3 If the location of the ligament of Treitz is abnormal, the study should be con- tinued to visualize the rest of the small intestine to the ileocecal junction, the distal end of the mesenteric root.1 Elective surgery is indicated in infants with repeated vomiting and imaging evidence of malrotation.
Midgut volvulus is true acute abdominal emer- gency resulting from strangulation of mesenteric vessels requiring urgent surgery. It occurs among patients with intestinal malrotation. The midgut is twisted around the narrow mesenteric root, which contains its vascular pedicle, namely the superior mesenteric artery and vein.
When torsion of the mesenteric vascular pedicle occurs,
FIGURE 9–5 ■ Positive “Meckel’s scan” using 99mTc-pertechnetate. Ectopic gastric mucosa in the Meckel’s diverticulum (arrow).
the superior mesenteric vein is compressed and col- lapsed, while more elastic superior mesenteric artery continues to allow the infl ow of blood into the volvu- lated segment, which becomes markedly congested.
Once the congestion becomes severe enough, the tissue pressure of the volvulated intestine eventually surpasses the blood pressure and results in necrosis of the entire midgut. This “strangulation sequence” may complete merely in a few hours. Thus, neonates and infants with bilious vomiting should be evaluated immediately and the possibility of midgut volvulus should be ruled in or ruled out. The upper GI series is the appropriate diagnostic procedure and, when positive, the distal duodenal obstruction can be demonstrated, with the volvulated segment as a spiral column (cork-screw appearance).2
Hypertrophic pyloric stenosis
US is the modality of choice when congenital hypertro- phic pyloric stenosis is suspected. The stomach should be fi lled at the time of examination; if it is empty, then
FIGURE 9–7 ■ Malrotation. A supine view from upper GI shows no fi xation of the ligament of Treitz and the proximal jejunum is in the right upper quadrant.
FIGURE 9–6 ■ Biliary atresia. US of the hepatic hilus (a and b) shows triangular hyperechogenicity (white arrow) correlat- ing an area of fi brosis and vestigial gallbladder (black arrow). Biliary scan (c) using 99mTc HIDA shows rapid hepatic tracer uptake but failure of excretion into the intestinal tract.
a
b
c
5% dextrose solution can be given orally prior to the study. Typical signs include pyloric muscle thickness
⬎4 mm, pyloric channel length ⬎17 mm, protrusion of pyloric mucosa in the fl uid-fi lled antrum (antral nipple sign), and gastric hyperperistaltis with failure of passage of gastric contents through the pylorus (Figure 9–8).
The numeric value for the lower limit of muscle thick- ness is variable in the literature, ranging between 3.0 and 4.5 mm. According to some of the authors, actual numeric value is less important than the overall mor- phology of the canal and the real-time observations.5 When US is not available or results are equivocal, an upper GI study can be helpful. This is able to demonstrate the presence of increased gastric peristalsis, a narrow, elongated pyloric channel, and characteristic compres- sion deformity at the distal gastric antrum and at the base of the duodenal bulb caused by the enlarged pyloric muscle.
Acute appendicitis
Both US and CT are adequate for evaluation of appen- dicitis and imaging strategy should be conformed con- sidering resources available at the individual institu- tion. US has a sensitivity of 80% with a specifi city of 94%.6 A graded compression technique is used where compression is applied during scanning utilizing the basic principle that normal appendix is easily com- pressible while infl amed appendix cannot be com- pressed. Compression also displaces the bowel gas and thus helps in visualizing the appendix. Typical diag- nostic fi ndings are a dilated, non-compressible, non- peristaltic appendix with a diameter of ⬎6 mm.
Additional fi ndings sometimes seen are the presence of an appendicolith, increased vascularity, and periap- pendiceal fl uid. Some of the limitations of US are:
(1)retrocecal appendix, which is diffi cult to fi nd on US
due to overlying gas in the cecum, (2) patients with high body mass index, and (3) perforated appendix in which the typical fi ndings may be absent due to decom- pression and disintegration of the appendix. CT with intravenous contrast is more sensitive (97%) than US for appendicitis and is helpful in those cases where US is diffi cult to perform or equivocal. Positive CT fi nd- ings are an enlarged appendix with a diameter of ⬎6 mm, presence of an appendicolith, adjacent fat strand- ing, and prominent enhancement of its wall. The full extent of perforated appendicitis, and abscess forma- tion can be better visualized on CT (see Chapter 21, Figure 21-16).
Intussusception
US is the diagnostic modality of choice when intussus- ception is suspected. The typical fi ndings are intraab- dominal mass with concentric rings of high and low echogenicity known as “target sign” on transverse plane and “pseudokidney sign” on the longitudinal plane (Figure 9–9). The presence of trapped fl uid in intussus- ception correlates significantly with ischemia and irreducibility.7 Lead points causing secondary intussus- ceptions, such as Meckel’s diverticulum, polyps, dupli- cation cysts, or lymphoma, can also be visualized on US.
Once the diagnosis is established, fluoroscopically guided hydrostatic or pneumatic reduction is indicated (Figure 9–10). CT and MRI are not utilized in the workup of intussusception. When the diagnosis is con- firmed on US, then fluoroscopic-guided reduction should be done. Pneumatic reduction is preferred over hydrostatic reduction as it is safer, faster, and cleaner.
During reduction, air pressure should not exceed 120 mm Hg. Successful reduction rate is around 80%
using the pneumatic technique, while the perforation rate ⬍1%.
FIGURE 9–8■ Idiopathic hypertrophic pyloric stenosis. A short-axis and a long-axis pyloric US (a and b) show thickened hypoechoic muscular layer with the elongated pylorus (A: gastric antrum; D: duodenal bulb). A prone view from upper GI (c) demonstrates elongated narrow pyloric channel (arrows) and characteristic deformity of the gastric antrum.
Meconium ileus
When congenital bowel obstruction due to cystic fi bro- sis is suspected, use of a moderately hyperosmolar water-soluble contrast enema, such as a half-strength Gastrografi n, can not only demonstrate the abnormal- ity, but can also hydrate and dislodge impacted tena- cious meconium in the dilated distal ileum. This is successful in about one-third of cases, avoiding surgery.
Hirschsprung’s disease evaluation requires a bar- ium enema. In this case, no cleansing enema should be given prior to the study, as the dilation of the rectum
caused by this intervention could mask the characteris- tic findings. In an unprepped barium enema, Hirschsprung’s is suggested when the maximum diam- eter of the rectum is less than that of the proximal sigmoid (rectosigmoid ratio ⬍1). The aganglionic segment may show tonic contraction (“saw-toothing”) (see Figure 19–6).
Acute pancreatitis
US is less sensitive than CT for the evaluation of pan- creatitis. The most common fi nding is focal or diffuse enlargement of the gland with a dilated pancreatic duct.
Other fi ndings are peripancreatic fl uid collection and decreased pancreatic echogenicity. CT is the investiga- tion of choice for the evaluation of pancreatitis. Typical fi ndings are pancreatic enlargement with heterogenous appearance (normal pancreas appears homogenous on CT), peripancreatic fat stranding, and dilatation of the pancreatic duct (Figure 9–11a). Other fi ndings may include extrapancreatic or intrapancreatic fl uid collec- tions. Complications of pancreatitis can also be visual- ized on CT. Pancreatic pseudocysts are seen as walled-off fl uid collections, most commonly in the lesser sac (Figure 9–11b).
Acute cholecystitis
US is the modality of choice for the diagnosis of both calculous and acalculous cholecystitis. Typical fi ndings include the sonographic Murphy’s sign (point tenderness at the gallbladder fossa during examination), gallblad- der wall thickening, and edema. Intramural edema appears as a band of hypoechogenicity in the wall. Gall- bladder wall thickening can be seen in other conditions
FIGURE 9–9 ■ Intussusception: transverse US image shows target sign (concentric rings of hyperechogenicity and hypoechogenicity).
FIGURE 9–10 ■ Pneumatic reduction of intussusception (prone views). Image “a” shows soft tissue density (black arrow) in the region of splenic fl exure. Image “b” shows subsequent migration of soft tissue density (white arrow) that is now lying in the region of hepatic fl exure.
including hepatitis, ascites, and heart failure but intra- mural edema is not seen and wall thickening in these conditions is typically homogenous.
Cholelithiasis
US is the primary modality for evaluation of gallstones.
They are typically echogenic, mobile, and produce a prominent acoustic shadow (Figure 9–12).Choledo- cholithiasis is usually due to migration of stones from the gallbladder to the common bile duct. US can dem- onstrate stones in the common bile duct but some- times it is diffi cult due to interposing gas in duode- num. US can also demonstrate biliary ductal dilatation secondary to choledocholithiasis. The internal diame- ter of the common bile duct should not be ⬎2 mm in infants or 4 mm in children older than 1 year.8 Biliary sludge on US appears echogenic without acoustic shadowing.