Emergency Department Body Imaging for the Sick Child

Epidemiology

Malrotation can be defined as a spectrum of congenital disorders leading to malposition of the bowel in the abdominal cavity due to abnormal rotation of the midgut about the axis of the superior mesenteric artery (SMA). The most acute complication of malrotation is midgut volvulus, a potentially fatal condition that can lead to bowel necrosis and requires immediate intervention. Approximately 75% of patients with symptomatic malrotation/volvulus present until the age of 5 years, with up to 60% of all cases presenting during the first year of life.

Clinical Features

In newborns, volvulus usually presents with bilious vomiting, while in older children the clinical symptoms vary widely from intermittent abdominal pain and malabsorption to acute onset of abdominal pain and vigorous vomiting.

Diagnostic Investigations

The current reference standard for radiological diagnosis of malrotation is upper gastrointestinal (UGI) series with barium. The preferable mode of administration of contrast is through a nasogastric (NG) tube. Aspiration of the stomach content is recommended prior to contrast administration, as an overdistended stomach may cause displacement of the duodenojejunal junction (DJJ) and obscure the duodenum. It is important to observe the initial passage of barium through the duodenum in real time. When the barium fills the more distal small bowel loops, the duodenum may become obscured, which may limit identification of the course of the duodenum and the position of the DJJ.

Once a small amount of contrast reaches the stomach, the child should be placed in the right decubitus position. This position helps evaluate the normal posterior extension of duodenum to the retroperitoneum. After the proximal duodenum is filled with contrast, the child should be positioned supine to assess the position of the DJJ. On frontal projection, the duodenum should extend leftward, crossing the midline, and the DJJ is normally located leftward of the left pedicle of the vertebra, at least as high as the inferior aspect of the duodenal bulb ( Fig. 12.1A ). Both frontal and true lateral views of the duodenum and DJJ are necessary to assess the rotation. Malrotation is suspected if, on frontal view, the DJJ is positioned medial to the left-sided pedicle ( Fig.12.1B ) or caudal to the duodenal bulb. On lateral view, a malrotated DJJ is positioned in an intraperitoneal location (more anterior than expected). If the imaging findings are equivocal, follow-through with delayed abdominal radiographs is recommended to identify the position of the cecum. The position of the cecum is not a specific finding and cannot exclude the presence of malrotation.

Midgut Volvulus

In midgut volvulus, the proximal small bowel twists around the superior mesenteric artery and vein. The most typical radiological sign of midgut volvulus is a “corkscrew” appearance of the proximal part of the small bowel ( Fig. 12.2A ). In patients with severe obstruction, beak-like tapering or abrupt “cutoff” of the duodenum may be identified, with lack of passage of contrast distally ( Fig. 12.2B ).

Summary

For diagnosis of midgut symptomatic malrotation/midgut volvulus in emergency settings:

• Use NG tube.

• Aspirate gastric content prior to contrast administration.

• Use small amount of contrast.

• Use right decubitus and true supine position to assess rotation.

• “Corkscrew” appearance or beak-like tapering of the proximal small bowel indicates midgut volvulus. The findings should be immediately reported to the referring service.

Epidemiology

Intussusception is an invagination of the proximal segment of bowel (intussusceptum) into the adjacent distal segment (intussuscipiens). In approximately 80% of cases, the intussusception occurs in the ileocolic area when the terminal ileum telescopes into the cecum and ascending colon. Nonreduced intussusception may cause bowel ischemia, necrosis, and perforation. Most cases of intussusception occur between 6 and 9 month of life.

Clinical Features

The “classic” clinical signs of intussusception are acute colicky abdominal pain, “currant jelly” or bloody stools, palpable abdominal mass, and/or vomiting.

Diagnostic Investigations

Abdominal radiographs cannot be recommended as a screening test for suspected intussusception, due to low sensitivity and specificity. The absence of ascending colon gas or soft tissue opacity within the right upper abdomen raises suspicion for intussusception. Supine and upright or left lateral decubitus views help to exclude free abdominal air in cases of perforation.

Abdominal ultrasound (US) serves as a first-line imaging modality in diagnosis of intussusception. It demonstrates 97.9% sensitivity and 97.8% specificity.

The US appearance of intussusception is often described as “target” or “donut” sign, which is related to the appearance of the intussusceptum within the intussuscipiens on transverse view ( Fig. 12.3A ). On the longitudinal view, intussusception may be reminiscent of kidney (“pseudokidney” sign), which corresponds to the relatively hypoechoic bowel wall surrounding hyperechoic mesenteric fat ( Fig. 12.3B ). Application of color Doppler contributes to the assessment of intussusception. The absence of blood flow within the wall of intussusceptum and intussuscipiens correlates with bowel ischemia. Other US findings that must be assessed and reported are free abdominal fluid and visualized “lead point” of intussusception, such as a bowel or mesenteric mass or cyst.

It is important to differentiate ileocolic intussusception (ICI) from small bowel-small bowel (SB-SB) intussusception. ICI requires treatment, while SB-SB intussusception is usually transient and in most cases resolves spontaneously. ICI is typically seen within the right abdomen, measuring more than 2.5 cm in diameter, and contains hyperechoic fat and internal mesenteric lymph nodes. Typical SB-SB intussusception with no lead point is usually smaller in diameter, and no internal mesenteric fat or lymph nodes are visualized. In most cases of ICI, the initial treatment of choice is nonsurgical reduction with an air or hydrostatic enema.

Summary

• Abdominal US is a first-line imaging modality in the diagnosis of intussusception.

• The presence of mesenteric fat and lymph nodes and the size of the intussusception help differentiate ICI from SB-SB intussusception.

Epidemiology

Hypertrophic pyloric stenosis is characterized by thickening of the pyloric muscle. It is considered an idiopathic condition and usually occurs in otherwise healthy infants between the third and twelfth weeks of life, most commonly in males and first-born infants.

Clinical Features

Thickening of the pyloris muscle causes symptoms of gastric outlet obstruction with projectile vomiting after feeds. If diagnosis is delayed, the infant can develop dehydration, weight loss, and electrolyte imbalances. In some cases, there is a palpable mass in the epigastric area known as “pyloric olive.”

Diagnostic Investigations

Pyloric US examination is a first-line imaging modality of choice, with almost 100% sensitivity and specificity. US should be obtained with a high-resolution linear transducer (5–12 MHz). Right posterior oblique positioning of the patient helps to visualize the fluid-filled antropyloric region. The US examination is considered positive for pyloric stenosis if it demonstrates thickening of a pyloric muscle of more than 3 mm and a pyloric canal length of more than 15 mm ( Fig. 12.4 ). On the longitudinal view, the appearance of hypertrophic pyloric stenosis has been described as “cervix” sign, resembling the uterine cervix.

In the absence of pyloric stenosis, the visualization of normal pylorus may become challenging. The visualization of opening of the pylorus and passage of the gastric contents through the pyloric canal in real time can help exclude pyloric stenosis.

In infant with vomiting, malrotation and midgut volvulus is the most important differential diagnosis of pyloric stenosis. US examination should include assessment of position and orientation of the SMA and the superior mesenteric vein (SMV). Abnormal SMA/SMV orientation is an indirect sign of malrotation and should be immediately reported to the referring team.

Summary

•Abdominal US is a modality of choice in the diagnosis of hypertrophic pyloric stenosis.

•SMA/SMV position should be assessed to exclude malrotation as a cause of vomiting.