The "whirl sign". True or False?
Poster No.:
C-0619
Congress:
ECR 2014
Type:
Educational Exhibit
Authors:
M. Pire, A. Verón Sánchez, M. Marti, M. Onate Miranda, C. Simón
Selva; Madrid/ES
Keywords:
Emergency, CT, Diagnostic procedure, Obstruction / Occlusion,
Volvulus
DOI:
10.1594/ecr2014/C-0619
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Learning objectives
To define the CT imaging features of the "whirl sign" and describe the pathologic
conditions in which this sign can be found, being most of them potentially lethal. We will
also describe other whirling appearance signs, more common but with less impact on the
therapeutic management and prognosis of the patient.
Background
The whirl sign was first described in 1981 by Fisher [1] and was found at a CT in a patient
with suspected chronic pancreatitis who really represented a case of malrotation and
midgut volvulus.
The "whirl sign" is defined as wrapped bowel loops encircling mesenteric vessels, which
act as an axis of rotation and determine cranio-caudally the direction of the twist:
clockwise or counterclockwise.
This sign is highly suggestive of intestinal volvulus in cases of intestinal obstruction, which
can be a life-threatening surgical emergency due to impairment of the vascular support
and intestinal ischemia. According to Duda et al. [3], in cases with small bowel obstruction
"a patient with the whirl sign on CT is 25,3 times as likely as a patient without the sign
to have SBO necessitating surgery".
Findings and procedure details
The "whirl sign": CT FEATURES
Suárez et al. [2] summarize the CT features of this sign:
•
•
Central vessels partly or entirely encircled by bowel loops.
Direction of the wrapping (clockwise or counterclockwise) in a craniocaudal fashion.
•
At least 90 of intestinal rotation.
Exclusion of cases in which the whirl only involves vessels or bowel.
Presence of large or small bowel obstruction.
•
•
o
Page 2 of 16
•
Associate findings: mesenteric vascular engorgement, mesenteric
hemorrhage, free intraperitoneal fluid, thickened bowel wall,
pneumatosis intestinalis.
As a result, the whirl sign has the appearance of a mass with iinternal swirling bands
of soft and fat tissue. Imaging has to be perpendicular to the axis of bowel rotation to
appreciate he whirl adequately.
Fig. 1: Axial contrast-enhanced CT images from cranial to caudal of a 57-year-old
patient with intestinal obstruction. Blue arrows are pointing bowel loops twisted around
mesenteric vessels, that is to say, the "whirl sign". This was an ileal volvulus. No
adhesions or ischemia were found in surgery.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
INTESTINAL VOLVULUS
Page 3 of 16
The whirl sign is seen in cases of malrotation and midgut volvulus, small bowel volvulus
of primary and secondary causes and large bowel volvulus.
MALROTATION AND MIDGUT VOLVULUS:
Intestinal malrotation is defined as a failure in normal rotation and fixation of the midgut
during fetal development. It is a generic term that includes a great variety of anomalies
in whose diagnosis the radiologist plays an important role.
Malrotation is asymptomatic and predisposes to midgut torsion or volvulation due to the
narrow mesenteric attachment of the bowel loops that often exists in these anomalies.
Therefore symptoms are secondary to midgut volvulus, that is to say obstruction
symptoms. Volvulation and symptoms can be intermittent.
The twisting is clockwise, whereas in small bowel volvulus can be clockwise or
counterclockwise.
Most of the symptomatic malrotations are seen in the first year of life. In adults,
malrotation is frequently and incidental finding and can be associated with a clinical
history of episodic abdominal pain, vomits or malabsorption due to intermittent and
chronic volvulus.
SMALL BOWEL VOLVULUS:
Small bowel volvulus can be primary or secondary:
- Primary or idiopathic: rare in developed countries and more common in young males
in countries of the Middle East, Asia and Africa [6]. There is no apparent cause, with no
predisposing anomalies present. It is said that dietary habits and variability in the length
and height of the mesentery are implicated factors.
- Secondary: due to congenital or adquired conditions such as malrotation, congenial
bands, postoperative adhesions, tumors, intussuspection, colostomy or internal hernias.
Adhesive bands and hernias are the most common causes.
Page 4 of 16
Fig. 2: Axial contrast-enhanced CT images show the "whirl sign" (yellow arrows) in
a 92-year-old patient with a closed-loop obstruction due to an adhesive band, and
subsequent jejunal volvulus.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
Page 5 of 16
Fig. 3: Axial contrast-enhanced TC images of the same patient with the "whirl
sign" (red arrows). This was a closed-loop obstruction and ileal volvulus due
to adhesion. There are signs of ischemia, like free peritoneal fluid and lack of
enhancement of the bowel wall.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
LARGE BOWEL VOLVULUS:
- Cecal volvulus: 25-40% of cases of colonic volvulus. They are usually associated with
fixation anomalies of the right colon to the retroperitoneum and abnormal motility of the
right colon. There are three types:
•
•
•
Type I or axial torsion
Type II or loop type
Type III or cecal bascule. In this third type, the cecum is located centrally in
the abdomen and there is a lack of the whirl sign.
Page 6 of 16
Fig. 4: Axial contrast-enhanced CT images showing a type I cecal volvulus, that is an
axial torsion of the cecum, which is located in the lower abdomen (red star). There is a
clockwise whirl sign (green arrows). The thin red arrow is pointing the collapsed right
colon.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
- Sigmoid volvulus: is the most common site of colonic volvulus (60-70% of cases).
Chronic constipation, sigmoid redundancy, high-fiber diet, pregnancy hospitalization or
Chagas disease are among the risk factors of this entity.
Page 7 of 16
Fig. 5: Axial contrast-enhanced CT image of a sigmoid obstruction in which the blue
arrow is pointing an abrupt change of caliber in the point of obstruction. No "whirl sign"
is apparently present.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
Page 8 of 16
Fig. 6: Coronal CT reconstruction of the same patient shows the "whirl sign" (blue
arrow). The sign is best appreciated if the scaning plane is perpendicular to the axis of
the twist.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
- Uncommon types: transverse (2-4% of colonic volvulus) and splenic angle volvulus
(<1%).
Page 9 of 16
DIFFERENTIAL DIAGNOSIS
Once the CT features of the whirl sign have been defined, we have to consider other
whirling patters that are not suggestive of a specific process and sometimes correspond
to anatomic variants.
THE BARBER POLE SIGN:
It was first described by Buranasiri et al [4] as an angiographic sign in a case of malrotation
and volvulus with counterclockwise twist of the mesenteric vessels upon themselves.
Subsequent cases reported in the radiological literature demonstrated that most of the
cases in which this sign was identified were not associated with malrotation or volvulus,
suggesting that the barber pole sign more probably represents a normal relationship
between the superior mesenteric vein and artery [7].
Page 10 of 16
Fig. 7: Axial contrast-enhanced CT images show the barber pole sign: a
counterclockwise twisting of the superior mesenteric vein (red thin arrow) around the
superior mesenteric artery.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
THE SUPERIOR MESENTERIC VEIN ROTATION SIGN:
This sign regards to the abnormal position of the mesenteric vein ventral and to the left
of the artery. It highly suggests intestinal malrotation, although this inverted position has
also be found in patients with normal intestine rotation.
Page 11 of 16
Additional findings that suggest malrotation must be identificated: abnormal position of
the duodeno-jejunal junction (to the right or under its normal position) with absence of
the normal right-left crossing of the duodenum under the superior mesenteric artery,
small or hypoplastic uncinate process of the pancreas and associated anomalies such
as Bochdaleck hernia, gastroschisis or omphalocele [5].
Fig. 8: Axial contrast-enhanced CT images in a patient with intestinal malrotation as
an incidental finding. On the left, the yellow arrow points the SMV and its abnormal
position on the ventral-left side of the SMA. The right CT scan shows malpositioning of
the duodenal-jejunal junction on the right (green arrow).
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
Page 12 of 16
Fig. 9: Axial contrast-enhanced CT image shows the position of the SMV on the left
side of the SMA. No malrotation was present. This case was a normal variant of the
relationship between the vein and the artery.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
VASCULAR "WHIRL-LIKE" PATTERNS:
As it was said before, the definition of the "whirl sign" excludes those cases that only
involve vessels. We include these vascular conditions in a group called "whirl-like"
patterns. They are unspecific and most of them no due to a pathological condition.
A common anatomic variant that can be sometimes misleading is the middle colic vein
draining in a swirling way.
However, we have identified these vascular whirls in cases of intestinal obstruction,
especially closed-loop obstructions. Therefore, this finding could suggest variable
Page 13 of 16
degrees of mesenteric torsion and complicated obstruction should be considered. Other
findings suggesting complication should be looked for (bowel wall thickening, free fluid,
mesenteric fat stranding, pneumatosis intestinalis…).
Fig. 10: Axial contrast-enhanced CT image in a patient with small bowel obstruction
due to incarcerated inguinal hernia. Thin yellow arrow is marking the middle colic vein
draining in a whirl-like pattern.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
Page 14 of 16
Fig. 11: Coronal contrast-enhanced CT image shows a whirl that involves mesenteric
vessels (red arrow), with no bowel loops encircling them. Thin yellow arrows point
Page 15 of 16
bowel loops with thickened and poorly enhanced wall. Surgery demonstrated a small
bowel obstruction due to adhesion with associate torsion of the mesentery. No signs of
ischemia were present.
References: Servicio de Radiología, Hospital Universitario La Paz, Madrid/ ES
Conclusion
The "whirl sign" is an uncommon sign highly suggestive of bowel volvulus, a life
threatening surgical emergency. Because of the consequences for the patient, the
radiologist must be familiarized with its imaging features and differentiate it from other
swirling patterns, more common but unespecific and sometimes related to normal
anatomic conditions.
Personal information
References
1. Fisher JK (1981). Computed tomographic diagnosis of volvulus in intestinal
malrotation. Radiology 140: 145-146.
2. Suárez Vega VM, Martí de Gracia M, Verón Sanchez A et al (2010). Trapped on the
"whirl": diagnostic sign on emergency CT. Emerg Radiol 17: 139-147.
3. Duda JB, Bhatt S, Dogra VS (2008). Utility of CT whirl sign in guiding management of
small bowel obstruction. AJR 191: 743-747.
4. Buranasiri SI, Baum S, Nusbaum M et al (1973). The angiographic diagnosis of midgut
malrotation with volvulus in adults. Radiology 109: 555-556.
5. Berrocal T, Gayá F, De Pablo L (2005). Aspectos embriológicos y radiológicos de la
malrotación intestinal. Radiología 47: 237-251.
6. Jaramillo D, Raval B (1986). CT diagnosis of primary small-bowel volvulus. AJR 147:
941-942.
7. Clark P, Ruess l (2005). Counterclockwise barber-pole sign on CT: SMA/SMV variance
without midgut malrotation. Pediatr Radiol 35: 1125-1127.
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