Purpose: To determine the characteristic ultrasound (US) findings of intussusception and to explain its different components.
Materials and methods: Three intussusceptions were surgically induced in pigs, and in vitro US scans were compared with the corresponding pathologic slices. US findings in 44 cases of pediatric intussusception confirmed by means of saline enema examination were analyzed.
Results: Axial images of intussusception showed a doughnut pattern. The hypoechoic external ring was formed by the everted returning limb of intussusceptum and, to a lesser degree, by the intussuscipiens. The doughnut's center varied according to the scan level. Scans obtained at the middle or at the base of the intussusception showed a characteristic hyperechoic crescent in all cases. This crescent was formed by the mesentery enclosing the entering limb of the intussusceptum, which the authors have termed the "crescent-in-doughnut sign". On scans obtained at the apex of the intussusception, the center was hypoechoic owing to the entering limb of the intussusceptum and the absence of the mesentery.
Conclusion: The crescent-in-doughnut sign appears to be a characteristic feature of intussusception.