DOI: 10.1148/radiol.2403040370
(Radiology 2006;240:910-911.)
© RSNA, 2006
The Whirlpool Sign1
Monica Epelman, MD
1 From the Department of Diagnostic Imaging, the Hospital for Sick Children, Toronto, Ontario, Canada. Received February 25, 2004; revision requested May 3; revision received June 5; accepted July 8.
Address correspondence to the author, Department of Radiology, the Children's Hospital of Philadelphia, 324 S 34th St, Philadelphia, PA 19104 (e-mail: monica_epelman{at}hotmail.com).
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APPEARANCE
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The whirlpool sign is found on transverse abdominal sonograms of newborns and young infants. This swirling, whirlpool-like shape is created when the superior mesenteric vein (SMV) and the mesentery wrap around the superior mesenteric artery (SMA) in a clockwise direction (Fig 1), which indicates midgut volvulus. Visualization is enhanced by the vascular signal at color Doppler flow US (1,2) (Fig 2).
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Figure 1: Transverse ultrasonographic (US) image through the mid-upper abdomen in a 7-month-old infant shows the whirlpool-like pattern of the SMV and the mesentery twisted around the SMA, which indicates midgut volvulus. The SMA (arrowhead) is seen in the middle of the volvulus, which is anterior to the aorta (arrow).
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EXPLANATION
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Midgut volvulus occurs when the bowel wraps around the SMA, creating a pattern reminiscent of a whirlpool (Fig 3). The intestinal tract and the mesenteric vessels become twisted, resulting in secondary venous engorgement. The SMV and its tributaries wrap around the SMA in a clockwise direction as a result of the volvulus. Shimanuki et al (3) found that the whirlpool sign consists of a side-by-side arrangement of vessels with opposing flow directions, indicating that the whirlpool contains not only the SMV and its tributaries but also branches of the SMA.
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DISCUSSION
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As the embryologic process of normal counterclockwise rotation is completed, the midgut (which is the portion of the bowel supplied by the SMA) becomes fixed and stabilized in its final position by the mesentery and peritoneum. The normal mesentery has a broad base, which extends from the left upper quadrant at the duodenojejunal junction (ligament of Treitz) to the cecum in the right lower quadrant. Midgut malrotation refers to a spectrum of congenital intestinal anomalies of position resulting from a nonrotation or an incomplete counterclockwise rotation of the primitive intestinal loop around the axis of the SMA during fetal development. The failure to complete rotation results in a narrow base of the mesentery, which can predispose the neonate to volvulus of the midgut (the subsequent twisting of the bowel around the SMA), which may or may not cause bowel obstruction. This volvulus is responsible for the whirlpool-like appearance on cross-sectional images (4–7). The direction of the volvulus should be clockwise, since Shimanuki et al noted a counterclockwise whirlpool in patients with enteritis (3). The whirlpool sign can aid diagnosis of midgut volvulus when seen on cross-sectional images, including those produced with computed tomography.
Midgut volvulus is a life-threatening emergency that can occur in the intestinal tract of a neonate. If not promptly diagnosed and treated, it leads to death or a lifelong dependence on total parenteral nutrition in survivors with short bowel syndrome. Although usually seen in the neonatal period, it may also occur later in life. Bile-stained emesis and occasional bloody stools are the main presenting clinical indicators and require a rapid imaging investigation (2,4).
Findings on abdominal radiographs are due to obstruction of the duodenum and/or bowel ischemia. Key signs of midgut volvulus include a jejunal bowel pattern on the right and variable degrees of duodenal obstruction due to peritoneal bands or a volvulus. The right lower quadrant may appear empty, since the malpositioned cecum often lies within the left hemiabdomen (2,4).
An important consequence of malrotation is malfixation of the intestines. Malfixation is inferred from malpositioning of the duodenojejunal junction or the cecum. Barium enema studies have fallen out of favor as the preferred diagnostic modality for malrotation, since the cecum may be positioned normally in as many as 20% of patients with malrotation (4).
In general, the diagnosis of this potentially fatal disorder is made by means of upper gastrointestinal (GI) series documenting the position of the duodenojejunal flexure. The location of the duodenojejunal flexure is an accurate indicator of malrotation and is classically depicted with the upper GI examination. The normal position of the duodenojejunal flexure is to the left of the pedicles of the spine and to the level of the duodenal bulb on an anteroposterior view of a well-positioned patient. Virtually all patients with malrotation will have a duodenojejunal flexure to the right of or below the normal position. The obstruction may be complete or partial, and sometimes the pathognomonic corkscrew pattern of the twisted duodenum and jejunum can be seen (2,4).
Learning to recognize the US findings of midgut volvulus is imperative, and it should always be considered in the differential diagnosis of abdominal pain in the pediatric population (7). For the neonate with the classic appearance of a whirlpool sign, additional imaging investigation is often unnecessary, and the surgeon should be alerted to plan for emergency surgery. At some institutions, diagnosis of volvulus with US alone indicates the need for surgery, whereas at other institutions require confirmation with a upper GI series (2,7). The advantages of US for this age group are apparent, since it can be performed at the bedside in intensive care units and lacks the adverse effects of ionizing radiation. In summary, the whirlpool sign is an indicator of midgut volvulus on transverse US studies and enables the imaging diagnosis.
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ACKNOWLEDGMENTS
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I am grateful to Alan Daneman, MBBCh, FRCPC, for his invaluable guidance and role as mentor and friend.
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FOOTNOTES
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| 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.
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References
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- Pracros JP, Sann L, Genin G, et al. Ultrasound diagnosis of midgut volvulus: the "whirlpool" sign. Pediatr Radiol 1992;22:18–20.[CrossRef][Medline]
- Berdon WE. The diagnosis of malrotation and volvulus in the older child and adult: a trap for radiologists. Pediatr Radiol 1995;25:101–103.[CrossRef][Medline]
- Shimanuki Y, Aihara T, Takano H, et al. Clockwise whirlpool sign at color Doppler US: an objective and definite sign of midgut volvulus. Radiology 1996;199:261–264.[Abstract/Free Full Text]
- Buonomo C, Taylor GA, Share JC Kirks DT. Gastrointestinal Tract. In: Kirks DR, Griscom NT, eds. Practical pediatric imaging. Philadelphia, Pa: Lippincott-Raven, 1998; 857–865.
- Bernstein SM, Russ PD. Midgut volvulus: a rare cause of acute abdomen in an adult patient. AJR Am J Roentgenol 1998;171:639–641.[Free Full Text]
- Berdon WE. Midgut volvulus with whirlpool signs [letter]. AJR Am J Roentgenol 1999;172:1689–1690.[Free Full Text]
- Patino MO, Munden MM. Utility of the sonographic whirlpool sign in diagnosing midgut volvulus in patients with atypical clinical presentations. J Ultrasound Med 2004;23:397–401.[Abstract/Free Full Text]
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