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some centers utilize prone films or left lateral decubitus radiographs to enhance
air movement into the cecum. In the patient with symptoms longer than 6 to 12
hours, flat and upright films often show signs of intestinal obstruction, including
distended bowel with air–fluid levels ( Fig. 116.5 ). A characteristic “target” sign
may be seen, or more commonly a paucity of gas in the right lower quadrant.
Occasionally, the actual head of the intussusception can be seen on a plain film as
a soft tissue mass ( Fig. 116.8A ).
US can be used diagnostically with reported sensitivity of 98% to 100%,
demonstrating the “target sign” on the transverse view and the “pseudokidney
sign” on the longitudinal view ( Figs. 116.8B and 116.8C ). Whether all patients
should have plain films prior to US is debatable. If signs of intestinal obstruction
or peritonitis, plain films may demonstrate pneumatosis or free air and thereby
expedite operative care. Oftentimes, the radiologist may request a plain film prior
to enema reduction but not necessarily before US. Plain films may be useful in
settings where US is not immediately available, in order to exclude a diagnosis of
intussusception when the pretest suspicion is low.
Hydrostatically controlled contrast enema or air insufflation enema has been a
successful therapy in up to 70% to 95% of cases with higher success rates
reported with air reduction. Strict reduction guidelines must be followed to avoid
perforation. The full reduction of the intussusception is confirmed only when
there has been adequate reflux of barium or air into the ileum. Patients with
peritonitis or free air on plain radiograph should not have an enema study or
reduction attempt. In the seriously ill infant with signs of peritonitis or a frank
small bowel obstruction, the diagnosis of intussusception can be made with
isotonic water-soluble contrast media with no attempt at reduction. The reduction
in such infants should be performed surgically. Perforation rates with enema
reduction have been reported in up to 3%. Risk factors for failed reduction and
perforation include: patient age younger than 3 months or older than 5 years; long
duration of symptoms, especially if greater than 48 hours; hematochezia;
significant dehydration; and evidence of small bowel obstruction on plain
radiograph.