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The Whirl Sign¹

¹ From the Department of Radiology, Brigham and Women’s Hospital, 75 Francis St, Boston, MA 02115. Received August 16, 2001; revision requested October 11; revision received January 14, 2002; accepted January 29. Address correspondence to the author (e-mail: bkhurana@partners.org).

Index terms: Intestines, CT, 74.12111 • Intestines, stenosis or obstruction, 74.7243 • Intestines, volvulus, 74.7243 • Signs in Imaging

	APPEARANCE

TOP APPEARANCE EXPLANATION DISCUSSION REFERENCES

 
At computed tomography (CT), the appearance of the "whirl sign" is that of a soft-tissue mass with an internal architecture of swirling strands of soft tissue and fat attenuation (Figure).

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Transverse CT scan of the pelvis. Engorged mesenteric vessels and collapsed distal ileum constitute the whirl sign (arrow) in a 44-year-old woman with surgically confirmed cecal volvulus.

	EXPLANATION

TOP APPEARANCE EXPLANATION DISCUSSION REFERENCES

	DISCUSSION

TOP APPEARANCE EXPLANATION DISCUSSION REFERENCES

 
Small-bowel obstruction can be distinguished into simple and closed-loop obstruction. The latter is a form of mechanical obstruction in which a segment of bowel is occluded at two points along its course. The pinching effect on the two ends of the bowel segment creates a narrow base of attachment, predisposing the closed loop to twist at its base, thereby producing volvulus. The subsequent impediment to the mesenteric vascular supply causes bowel anoxia and strangulation, which is defined as an intestinal obstructive process associated with intestinal ischemia (3). Thus, it is imperative to select carefully the patients for whom a trial of conservative nonsurgical treatment can be proposed, instead of urgent surgical exploration. The role of CT in the diagnosis of ischemia in patients with suspected small-bowel obstruction has been analyzed in the literature with reported 83% sensitivity, 93% specificity, and 91% accuracy (4).

Small-bowel volvulus is a rare but life-threatening surgical emergency. On the basis of its cause, volvulus of the small intestine can be differentiated into two types: primary volvulus, in which there are no predisposing anatomic abnormalities (idiopathic), and secondary volvulus, in which a congenital or acquired abnormality causes rotation of the bowel (3). The most frequent causes of secondary volvulus are postoperative adhesions, in which the intestine is fixed to a point that acts as a pivot, and hernia. Early preoperative investigation and expedient surgical treatment are required if bowel infarction is to be prevented.

The whirl sign described by Fisher (1) was found at CT in a case of midgut volvulus, where the center of the whirl was the superior mesenteric artery and the whirled appearance was created by the encircling loops of bowel. It was proposed that any disturbance in the normal 270° counterclockwise return of the intestine into the abdominal cavity could produce a range of rotational and attachment abnormalities and that the lack of normal peritoneal attachment predisposes development of a volvulus, with twisting occurring around its attachment point and fulcrum, the superior mesenteric artery.

Subsequent to Fisher’s article (1), many authors described various forms of volvulus. Shaff et al (5) extended the definition of the whirl sign to include the CT appearance of sigmoid volvulus, where a whirl was formed by the afferent and efferent loops, leading into the volvulus with the central portion composed of tightly twisted bowel and mesentery. They commented that the tightness of the whirl was proportional to the degree of rotation. Frank et al (6) demonstrated the whirl sign associated with cecal volvulus, where the actual whirl comprised the twisted mesentery, as well as collapsed cecal and distal ileal loops. The abrupt termination of the dilated bowel segments in the region of the whirl is highly suggestive of volvulus and presumably either occurs acutely or is related to decrease of both inflow and secretion of fluid.

The key feature that indicates a bowel volvulus is the presence of the whirl sign. Most important, the whirl sign may not be as apparent if the axis of rotation is not perpendicular to the transverse scanning plane. It is to be noted that the affected mesenteric vessels are typically not seen at the same anatomic level where a closed loop obstruction is "pinched off" at the site of constriction. Other CT signs of small-bowel volvulus described in the literature are a radial distribution or a U-shaped configuration of the distended bowel loops and a triangular section or longitudinal tapering of the collapsed bowel loop at the site of torsion. Both of these CT signs may also be observed in a closed-loop obstruction of the small bowel and may depend on the length of the obstructed segment, the degree of bowel distention, and the orientation of the closed loops in relation to the transverse scanning plane.

Blake and Mendelson (7) described the presence of the whirl sign in a few patients following surgeries that involved bowel manipulation (eg, hemicolectomy) and proposed that the sign was nonspecific. Although these surgeries can rotate the bowel and mesentery by as much as 180°, it is extremely rare to cause a 360° or more rotation to give the appearance of whirl sign. Thus, volvulus continues to be the diagnosis of exclusion in the presence of the whirl sign, even in such patients.

In conclusion, the whirl sign is highly suggestive of intestinal volvulus and should raise suspicion for complicated closed-bowel obstruction.

	ACKNOWLEDGMENTS

 
Special thanks to Stephen M. Ledbetter, MD, and Pablo R. Ros, MD, for their guidance in preparing this manuscript.

	FOOTNOTES

 
A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.

	REFERENCES

TOP APPEARANCE EXPLANATION DISCUSSION REFERENCES

 

1. Fisher JK. Computed tomographic diagnosis of volvulus in intestinal malrotation. Radiology 1981; 140:145-146.[Abstract/Free Full Text]
2. Moore CJ, Corl FM, Fishman EK. CT of the cecal volvulus. AJR Am J Roentgenol 2001; 177:95-98.[Free Full Text]
3. Blathazar EJ, Birnhaum BA, Megibow AJ, Gordon RB, Whelan CA, Hulnick DH. Closed loop and strangulating intestinal obstruction: CT signs. Radiology 1992; 185:769-775.[Abstract/Free Full Text]
4. Balthazar EJ, Liebeskind ME, Macari M. Intestinal ischemia in patients in whom small bowel obstruction is suspected: evaluation of accuracy, limitations, and clinical implications of CT in diagnosis. Radiology 1997; 205:519-522.[Abstract/Free Full Text]
5. Shaff MI, Himmelfarb E, Sacks GA, Burks DD, Kulkarni MV. "The whirl sign": a CT finding in volvulus of the small bowel. J Comput Asst Tomogr 1985; 9:410.[CrossRef][Medline]
6. Frank AJ, Goffner LB, Fruauff AA, Losada RA. Cecal volvulus: the CT whirl sign. Abdom Imaging 1993; 18:288-289.[Medline]
7. Blake MP, Mendelson RM. The whirl sign: a non-specific finding of mesenteric rotation. Australas Radiol 1996; 40:136-139.[Medline]

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				J. B. Duda, S. Bhatt, and V. S. Dogra Utility of CT Whirl Sign in Guiding Management of Small-Bowel Obstruction Am. J. Roentgenol., September 1, 2008; 191(3): 743 - 747. [Abstract] [Full Text] [PDF]

				P. S. Sandhu, B. N. Joe, F. V. Coakley, A. Qayyum, E. M. Webb, and B. M. Yeh Bowel Transition Points: Multiplicity and Posterior Location at CT are Associated with Small-Bowel Volvulus Radiology, October 1, 2007; 245(1): 160 - 167. [Abstract] [Full Text] [PDF]

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