Gastrointestinal tract images Although conventional abdominal radiographs are often obtained first, their value has been questioned. Even experienced observers often differ whether in children with clinically suspected intussusception it is indeed present or absent; the best predictor of intussusception is a soft tissue mass and decreased large bowel gas.
This is radiology images of Ileocolic intussusception. A: CT scout view identifies an intussusception (arrow) in a 7–year-old. Burkitt’s lymphoma was the lead point. B: Intussusception in a 10–month-old infant with pain and palpable right upper quadrant mass. A conventional radiograph reveals a soft-tissue tumor in region of transverse colon (arrows). A barium enema confirmed intussusception.
In some centers, US is the initial imaging modality of choice when suspecting an intussusception. In experienced hands US has a high sensitivity and specificity in detecting an intussusception and a contrast enema is then limited to therapy. Viewed in a transverse section, prereduction US shows an intussusception as a doughnut or target lesion; it has a reniform shape (pseudokidney is the term often used) when viewed in longitudinal section. Scans close to the lead point of an intussusception reveal the intussusceptum as a hypoechoic central structure; scans away from the lead point have a hyperechoic crescent appearance due to mesentery and related vessels being drawn in by the intussusceptum. Although such a US appearance should suggest an intussusception, neither a target nor reniform appearance is pathognomonic. Necrotizing enterocolitis, volvulus, or even stool may mimic this appearance.
At times, because of obscure symptomatology, these patients are studied with CT. Findings of intussusception are straightforward in most. Computed tomography reveals an intraluminal tumor and a target sign–like appearance of alternating layers of high and low attenuation. With obstruction, more proximal bowel loops distend with fluid. Necrosis manifests as inflammation, loss of tissue planes, and presence of intraperitoneal fluid. An extensive ileocolic intussusception distorts normal superior mesenteric vessel anatomy. Thus with the lead point of an intussusceptum at the sigmoid colon or distally, the superior mesenteric vein is located to the left of the superior mesenteric artery.
Published successful intussusception reduction rates range between 70% and 85%, with an occasional report of 90%, regardless of whether a liquid or air is used. A comparison of different contrast agents used is difficult unless the procedure used is standardized. A major factor influencing success rates is the intraluminal pressure achieved rather than any other technical factor.A barium enema bag at 1-m elevation produces greater intraluminal pressure than a typical water-soluble contrast agent or water at the same height. Pressure during pneumatic reduction varies considerably.
At times US identifies fluid within an intussusception, representing trapped peritoneal fluid, seen on axial images as an anechoic crescent between the intussusceptum and intussuscipiens. Ultrasonography during reduction of an ileoileocolic intussusception reveals a complex frond-like appearance. The intussuscepted small bowel is also surrounded by cecal fluid. These intussusceptions are likewise difficult to reduce.
Radiology images of Ileocolic intussusception due to large lymph nodes in a 10–year-old. A: CT detects an intraluminal right colic tumor (arrows) suggesting an intussusception. The intussusceptum is seen as a target lesion on a transverse US scan (B) and as an oval tumor on a longitudinal scan (C).Surgery revealed enlarged nodes as a lead point but no neoplasm was identified.