Intussusception occurs when one segment of bowel is pulled into itself (or a neighboring loop of bowel) by peristalsis.

A proximal part of the bowel is pulled into the distal lumen and peristalsis pulls it forwards as if it were a bolus of food. The prolapsing part of the bowel is described as the intussusceptum while the distal segment of bowel receiving the intussusceptum is described as the intussuscipiens.

When intussusception occurs in adults, it is usually caused by a focal lesion acting as a lead point.

On ultrasound the characteristic target sign consists of concentric alternating echogenic and hypoechoic bands. The echogenic bands are formed by mucosa and muscularis, whereas the submucosa is responsible for the hypoechoic bands.

The case is courtesy of Dr Wael Farouk, general surgery consultant, RCMC.