Answer: B) Air or water-soluble contrast enema

Diagnosis: Intussusception

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