Table 2.

Differential diagnosis table for an internal hernia based on causes of small-bowel obstruction after a laparoscopic Roux-en-Y gastric bypass.

	X-ray	US	CT	MRI
Internal hernia	-Non-specific -When small bowel obstruction (SBO) is present- dilated loops of small bowel with air-fluid levels	-Of limited value	-Compression of the main stem of the superior mesenteric vein (SMV “beaking” sign) -Swirled appearance of mesenteric fat or vessels at the root of the mesentery (the swirl sign) -SBO and mesenteric edema can be present	-Not routinely used -T2-weighted fast imaging techniques: can match some less specific CT signs, such as clustered loops, dilated and displaced bowel loops, or mesenteric edema
Adhesions	-Non-specific; dilated bowel loops proximal to the place of obstruction and air-fluid levels -Absence of gas in the distal collapsed bowel	-Of limited value	-An abrupt transition point from dilated to collapsed bowel segments	-Not routinely used in an emergency situation
Anastomotic strictures	-Radiography with contrast material-delay in the passage of contrast through the anastomosis -Dilated bowel loops with air-fluid levels proximal to obstruction	-Of limited value	-Narrowing at the level of anastomosis with bowel obstruction proximal to it	-Not routinely used
Incisional hernia	-Dilated loops of bowel with air-fluid levels proximal to the place of obstruction -Absence of gas in the distal collapsed bowel	-Defect in the abdominal wall with the herniation of a bowel loop	-Herniation of a bowel loop through a defect in the abdominal wall -Dilated bowel loops proximal to the hernia and collapsed or normal bowel distal to the obstruction	-Not routinely used
Intussusception	-May demonstrate a soft tissue mass -Dilated obstructed bowel loops with air-fluid levels	-Modality of choice in the pediatric population -Can demonstrate the characteristic appearance of the target sign	-Characteristic appearance with bowel-within-bowel configuration	- T2-weighted fast imaging techniques: bowel within-bowel configuration
Bezoar	-Usually not possible to identify a bezoar on radiographs alone -Dilated obstructed bowel loops with air-fluid levels in patients with SBO	-Hardly visible due to the accumulated gas in the bowels affecting the ultrasonic sound -Intraluminal mass with a hyperechoic arc-like surface casting a posterior acoustic shadow	-Obstructive inhomogeneous mass with regular margins mottled with gas bubbles -Dilated bowel proximal to the mass	- T1- and T2-weighted fast imaging techniques: ovoid mass containing mottled low signal intensities, which represent air bubbles