The Whirlpool Sign in Midgut Volvulus

A 21-year-old girl presented to the emergency department with acute colic abdominal pain, and 6-hour history of nausea and vomiting. She had been previously diagnosed with irritable bowel syndrome attributed to intermittent changes in intestinal motility. On physical examination, she had a palpable tender epigastric mass. Laboratory studies were unremarkable.

Abdominal radiograph revealed no free air under the diaphragm. Moderate gastric distention and some colonic intestinal loops were slightly dilated (Fig.1). The diagnosis remained obscure until a contrast-enhanced computed tomography (CT) was performed. The abdominal CT scan revealed a swirling appearance of the bowel and mesentery twisted around the superior mesenteric artery axis ("whirlpool sign") (Fig.2). The superior mesenteric vein (SMV) was to the left of the superior mesenteric artery (SMA) (Fig.3 – vein marked with blue arrow and artery with red arrow). There was also an abnormal configuration of the small bowel, with duodenum D3 and D4 located to the right of the spine and intestinal loops predominance on the right abdomen (Fig.4). Moderate gastric distention was noticed, and a few colon loops were dilated on the left abdomen. Nevertheless, there were no signs of vascular commitment or bowel parietal thickening. There was also no intra-abdominal free fluid or pneumoperitoneum.

Congenital intestinal malrotation is a direct consequence of an anomalous embryogenic stage where the bowel should undergo its physiological 270º counterclockwise rotation around the axis of the SMA (1). The lack of physiological rotation of the bowel leads to different grades of abnormalities, including the entire small bowel remaining on the right side of the abdomen, while the caecum, appendix and colon stay on the left side, and the ligament of Treitz is absent (2). Furthermore, the mesentery may acquire a vertical attachment and the peritoneal fibrous bands responsible for fixing the duodenum and the caecum to the abdominal may persist. As the intestinal structures are abnormally placed, these congenital bands, known as Ladd’s bands, may compress the duodenum and can potentially cause duodenal obstruction (3). The abnormal rotation of the gut and lack of posterior peritoneal fusion predisposes to midgut volvulus and internal hernias. The overall incidence of small bowel malrotation is unknown once some patients remain totally asymptomatic for life.

The clinical presentation correlates with the age of onset symptoms with neonates and children commonly presenting with midgut volvulus, while only 15% of the adults have this form of presentation (4). Midgut volvulus is a complication of intestinal malrotation in which clockwise twisting of the bowel around the SMA axis occurs because of the narrowed mesenteric attachment (5). It is a potentially life-threatening complication and requires emergency surgery. Frequent episodes of abdominal pain and vomiting during a period of several months or years should raise clinical suspicion and may lead to imaging investigation (6). The abdominal radiographs findings in midgut volvulus are usually abnormal but unfortunately non-specific. CT is very helpful in midgut malrotation diagnosis once its imaging findings are characteristic. The whirlpool sign is defined by the swirling appearance of the bowel and mesentery twisted around SMA axis (7). The abnormal SMA-SMV relationship can also be detected by abdominal ultrasound. Some patients may present a combination of midgut volvulus and internal hernias at the same time. The management of symptomatic midgut volvulus requires surgical intervention and the laparoscopic Ladd’s procedure should be performed in all patients with intestinal malformation. In this procedure, a counterclockwise detorsion of the bowel and a surgical section of the fibrous Ladd's bands is performed, with small bowel and mesentery relocation to its normal place, which was the case of our patient. Additionally, during the procedure, the small bowel is placed along the right lateral gutter and colon on the left, and additional appendectomy also performed (8). These life-threatening events with atypical presentation in adults emphasize the importance of earlier detection and treatment.

Teaching Points

• The diagnosis of small bowel malrotation after childhood is difficult and often leads to diagnostic and treatment delay with possible bowel ischemia and necrosis.
• CT scanning is considered the imaging modality of choice as it can show the pathognomonic whirlpool sign of midgut volvulus.
• It is extremely important to keep a high index of suspicion for this unsuspected condition and recognize that surgery may be lifesaving.