Imaging description

“Idiopathic” intussusception refers to distal small bowel lymphoid hyperplasia causing invagination of the ileum into the proximal colon. Such ileocolic intussusceptions without a discrete lead point and comprise the vast majority (>90%) of all pediatric intussusceptions [1].

Ultrasound is the preferred diagnostic modality for intussusception evaluation. An intussusception’s characteristic ultrasound appearance is a right abdominal mass exhibiting a swirled pattern of alternating hyperechogenicity and hypoechogenicity when the bowel is scanned transverse (Figure 91.1). This pattern of concentric rings represents alternating layers of mucosa, muscularis, and serosa. Names given to this appearance include “doughnut sign” and “pseudo-kidney” [2–4]. In longitudinal view, this bowel invagination and its various layers may resemble a sandwich (“sandwich sign”) [5].

Several accompanying sonographic features have been assessed for their ability to predict reducibility and/or bowel necrosis. These include thickness of the peripheral hypoechoic ring, the presence of fluid either trapped in the intussusception or within the peritoneal cavity, and presence of blood flow in the intussusception on Doppler interrogation [6, 7–13]. In aggregate the literature has been controversial regarding their respective prognostic abilities, rendering it difficult to predict which intussusceptions will reduce with enema or progress to bowel inviability [1].