The Swirl Sign and Internal Hernias

Gastric bypass, a one-shot surgical solution for complex, life-long psychosocial issues, has become routine therapy for morbid obesity, with laparoscopic Roux-en-Y being the most commonly performed bariatric procedure in many institutions. Internal hernias, which are more common after laparoscopic gastric bypass than after open gastric bypass, are a dreaded complication. The presentation is often nonspecific, making CT an important part of diagnosis.

A number of CT findings have been associated with internal hernias. The best single predictor of internal hernia is the mesenteric swirl (or whirl) sign: The swirled appearance of vessels and fat at the mesenteric root (see video, which may be blocked by Websense). The problem with the swirl sign is that mesenteric swirling can be seen in healthy persons and post-laparoscopic Roux-en-Y gastric bypass patients without an internal hernia, so the finding must be considered in conjunction with the clinical picture.

The degree of swirl may be used to increase confidence. In one series, all cases of mesenetric swirl of at least 270° were associated with a hernia at surgery. In patients with a mesenteric swirl but no hernia at surgery, the median amount of swirl was less than 90°.

References

• Iannuccilli JD, Grand D, Murphy BL, Evangelista P, Roye GD, Mayo-Smith W. Sensitivity and specificity of eight CT signs in the preoperative diagnosis of internal mesenteric hernia following Roux-en-Y gastric bypass surgery. Clin Radiol. 2009 Apr;64(4):373-80.
• Lockhart ME, Tessler FN, Canon CL, Smith JK, Larrison MC, Fineberg NS, Roy BP, Clements RH. Internal hernia after gastric bypass: sensitivity and specificity of seven CT signs with surgical correlation and controls. AJR Am J Roentgenol. 2007 Mar;188(3):745-50.