Imaging description

The widespread use of CT has led to increased detection of small bowel intussusceptions (SBI) [1], which are identified in 0.5% of non-selective abdominal-pelvic CTs [2].

An intussusception occurs when a segment of bowel and its mesentery (the intussusceptum) invaginates or telescopes into a contiguous segment of bowel (the intussuscipiens) [1]. An intussusception may be identified on CT, MRI, ultrasound, or fluoroscopy.

On contrast-enhanced CT, a bowel within bowel appearance is noted. On transverse short axis images through the bowel, a classic “target” appearance results if mesenteric fat is visible between the two segments of bowel in the intussusceptum, and/or fluid is present between the intussusceptum and intussuscipiens (Figure 62.1). On a longitudinal view, similar structures may be identified in a “sausage-shaped” mass."

Similar corresponding findings are noted on ultrasound, where they may be referred to as the “doughnut sign” on a transverse image or the “sandwich sign” on a longitudinal image [3].

Importance

Small bowel intussusception accounts for 5–16% of adult intussusceptions [4]. In the past, the standard of care for intussusception in adults was surgical resection to treat symptoms and for pathologic evaluation [5], as malignancy was reported in 24% of enteric intussusceptions and 54% of colonic intussusceptions [6]. These data were generally based on surgical series in patients with obstructive symptoms and intraoperative diagnoses [2]. These studies clearly would not have included many of the transient SBI currently detected on imaging, which explains the different rates of pathology associated with SBI in more recent studies.