Ultrasound in Pediatric Emergencies

Gaurav Saigal, MD, Jennifer Runco Therrien, MD, and Frank Kuo, BS

Disclosures

Appl Radiol. 2014;43(8) 

In This Article

Abdominal Pathology

Malrotation and Volvulus

Intestinal malrotation is a developmental abnormality leading to a decrease in the length of the mesenteric root, predisposing the midgut to rotation. One of the most dangerous sequelae of malrotation is volvulus, a medical emergency that causes bowel obstruction, ischemia of and necrosis of the affected intestine. Patients can present with bilious vomiting, failure to thrive, abdominal pain and other nonspecific symptoms. Although an upper gastrointestinal (UGI) contrast study is the gold standard of diagnosis, US can also be useful, particularly when results of the UGI study are equivocal. On US, the anatomical relationship of the superior mesenteric artery (SMA) and superior mesenteric vein (SMV) may be reversed (Figure 2A). Normally, the SMV is to the right of the SMA. With midgut volvulus, the SMV may occupy a position directly anterior or to the left of the SMA. It is important to note, however, that a normal SMA/SMV relationship does not exclude volvulus and the UGI study remains the imaging gold standard. Conversely, some children without volvulus may have a vertical or inverted SMA/SMV relationship.[2]

Figure 2.

An 8-month-old presented to the ED with bilious vomiting. Gray-scale (A) and color Doppler (B) images demonstrate the SMV (long white arrow) curving anterior and to the left of the SMA (black arrow). On the color Doppler image, there is twisting of the mesenteric vessels (short white arrows) around the SMA (black arrow), also known as the "whirlpool" sign of volvulus.

On US, twisting of the mesenteric vessels and superior mesenteric veins (SMV) around the superior mesenteric artery (SMA) can produce a "whirlpool sign" on color Doppler US (Figure 2B).[3] Other US signs of volvulus include the "hyperdynamic pulsating SMA" or the "truncated SMA" sign.[4,5]

Pyloric Stenosis

Although not a true emergency, pyloric stenosis is common in the ED. Pyloric stenosis occurs when hypertrophy of the pyloric muscle causes narrowing, resulting in projectile non-bilious vomiting. The physical exam may reveal an olive-shaped mass in the right upper quadrant of the abdomen. US is the modality of choice when suspecting pyloric stenosis.[6] The main diagnostic criterion is a measurement of greater than 3mm in the thickness of the muscular layer of a single wall of the pylorus (Figure 3). Elongation of the canal greater than 12mm has also been reported as an abnormal finding, but is less reliable due to the difficulty in achieving reproducible measurements.[7] Other findings include hypertrophy of the mucosa, gastric distension with active peristalsis and redundant mucosa protruding through the antrum. Some technical maneuvers which might be useful while performing the US include laying the patient right-side down (allowing gas to move away from the pylorus), use of sugar water to feed (not only helps in calming the baby but also provides a good acoustic medium for the ultrasound beam) and observing the pylorus during the study for any passage of stomach content through the pyloric channel.[8]

Figure 3.

A 4-week-old boy with non-bilious vomiting. Axial (A) image of the right upper quadrant demonstrates a hypoechoic rounded structure (black arrow) posterior to the gallbladder (long white arrow) consistent with the pylorus. Longitudinal image (B) demonstrates the elongated and thickened pylorus, with each muscular wall measuring 5 mm and the length as 21.5 mm, consistent with hypertrophic pyloric stenosis. The centrally seen echogenic linear bands (short white arrows) represent the mucosa and should not be included in the measurements.

Intussusception

Intussusception occurs when part of the intestine invaginates or telescopes into a distal portion of bowel, causing obstruction. Symptoms include nausea, vomiting, crampy abdominal pain, and rectal bleeding classically described as "red currant jelly." Most patients are between the ages of 6 months and 2 years. Prognosis is improved by early diagnosis. US has a high sensitivity of 98-100% and specificity of 88–100%.[9] US findings include a soft-tissue abdominal mass corresponding to the intussusception. The intussusception appears as a "target" or "donut" sign (Figure 4) created by the receiving bowel loop- intussuscipiens, and the proximal prolapsing bowel loop- intussusceptum, with echogenic intervening mesenteric fat. Another US appearance described is the "pseudokidney" sign, when mesentery containing fat and vessels are dragged into the intussusception, suggesting the US appearance of the renal hilum, with the apparent renal parenchyma formed by the surrounding edematous bowel.[10] Ultrasound can also be useful in detecting a lead point, such as lymph nodes, polyps, duplication cysts (Figure 5) and Meckel's diverticulum, among others. Trapped fluid within the intussusception (Figure 5) and absence of blood flow to the bowel on Doppler imaging have been described as signs of ischemia and decreased reducibility .[9] Recently, successful reduction with ultrasound-guided hydrostatic pressure has been performed in some institutions.[11]

Figure 4.

Ultrasound of the mid abdomen of a 1-year-old with abdominal distension and bloody stools. A rounded mass having a 'target-like' appearance consistent with an intussusception is noted in the upper abdomen (A). Longitudinal image (B) of the mass nicely depicts the intussusceptum (short white arrow) protruding into the intussuscipiens (short black arrows). The echogenic structure between the bowel loops (long white arrow) represents the mesenteric fat caught in the intussusception. Doppler image (C) demonstrates preserved vascularity in the intussuscepted bowel. Image (D) demonstrates multiple enlarged mesenteric lymph nodes (long black arrows) in the vicinity, felt to be the leading point for the intussusception.

Figure 5.

A 9-month-old child with increased fussiness and blood-tinged stool. Ultrasound images of the right lower quadrant (A-C) demonstrate a rounded mass consistent with an intussusception. A rounded cystic structure demonstrating "gut" signature (white arrow) was noted within the intussusception (white arrow), suggesting a duplication cyst. A small amount of free fluid was noted within the loops of the intussusceptum (black arrow), considered to be a sign of decreased reducibility and ischemia.

Appendicitis

Appendicitis is the most common childhood surgical emergency. The diagnosis is challenging, particularly in younger children, potentially leading to a false negative diagnosis with potential for perforation and other complications. Although primarily a clinical diagnosis, imaging studies can aid in confirmation and reducing the number of negative appendectomies. US has a sensitivity of 88% and specificity of 94% according to a meta-analysis of studies from 1986 to 2004.[12] US evaluation is performed using a high frequency linear transducer and graded compression technique. Gentle pressure is applied to the right lower quadrant to displace normal bowel loops and ascertain the position of the nonperistaltic cecum. The appendix usually lies just lateral to the cecum and anterior to the iliac vessels. Positive findings of appendicitis include an outer diameter greater than 6 mm, a noncompressible lumen arising from the base of the cecum, echogenic periappendiceal inflammatory fat changes, an appendicolith or a periappendiceal fluid collection (Figures 6 and 7). Enlarged mesenteric lymph nodes or signs of a perforated appendix such as an abscess can also be seen.

Figure 6.

Ultrasound images of the abdomen in a 5-year-old child presenting with right lower quadrant pain (A, B). A dilated fluid-filled tubular structure demonstrating increased vascularity is noted in the right lower quadrant (short white arrows). Transverse images of the dilated structure demonstrate a diameter of 1.4 cm, as well as non-compressibility, findings consistent with appendicitis.

Figure 7.

Ultrasound of the abdomen in a child presenting with pain for the past two days demonstrates a collection in the right lower quadrant with an underlying tubular structure (short white arrows), felt to represent a ruptured appendicitis, which was confirmed at surgery.

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