The post-reduction donut sign.

A donut-shaped intestinal structure in the lower right abdomen, observed during abdominal ultrasound investigation following nonoperative intussusception reduction, may create a diagnostic problem concerning differentiation from a residual or recurrent intussusception or underlying small bowel disease. In 30 cases of ileocolic intussusception an abdominal ultrasound examination was performed after reduction, the success of which was proven by radiological and clinical criteria. More than half of the examinations showed an aperistaltic "donut" in the ileocecal region which was similar to the target sign commonly seen in intussusception. Differentiation was possible according to the following two criteria: first, the diameter of the donut was smaller than that of the original target sign seen in these patients. Second, the donut consisted of a broad hypoechoic rim and an echogenic center, whereas the target was normally composed of multiple concentric rings. One third of the patients showed localized thickening of the walls of the distal ileal loops which did not cause diagnostic problems. All of the suspicious intestinal structures disappeared within the first 5 days following reduction. It is our opinion that the post-reduction donut correlates with significant edema of the ileocecal valve and does not represent a mechanical lead point or persisting residual intussusception.