Imaging Case: Answer
Answer: B) Air or water-soluble contrast enema
Cause: A proximal portion of bowel enters a distal portion and then is pulled further forward via peristalsis. The site at which it occurs is thought to be a disruption in the smooth contour of the bowel, referred to as a lead point. This may be enlarged lymphatic tissue, tumor, polyp, or classically, in children, Meckel’s diverticulum. If the intussusception remains for a long period of time, the involved bowel may become edematous, which may compromise blood flow. If this progresses it may result in ischemic bowel.
Presentation on Imaging:
Plain Film: Signs of bowel obstruction: air-fluid levels, decreased bowel gas in distal portions of bowel
Ultrasound: “Target sign”: Seen in a cross section of the telescoped bowel as depicted below and in the case above
“False Kidney Sign”: Seen in a longitudinal view of the intussusception, the entering and returning proximal bowel forms the hypoechoic area. When mesentery is pulled into the process it creates a hyperechoic center, creating the “pseudokidney” sign as seen in the examples below.
“Crescent In a Donut Sign”: When mesentery has been pulled into the intussusception, it creates an echogenic semi-circle within the target sign that appears like a crescent:
Imaging of Choice:
1. Ultrasound: Has a false negative rate approaching zero. Multiple studies demonstrate ultrasound to be 100% accurate.
2. Plain Abdominal Film: Very low sensitivity
3. CT abdomen