Abdominal X-ray
Abnormal bowel gas pattern
Volvulus
Twisting of the bowel, or volvulus, is a specific cause of bowel obstruction which can have characteristic appearances on an abdominal X-ray.
The two commonest types of bowel twisting are sigmoid volvulus and caecal volvulus.
Key points
- Volvulus is a specific cause of obstruction with characteristic X-ray appearances
Sigmoid volvulus
Unlike the majority of the large bowel, the sigmoid colon has its own mesentery. It is therefore more prone to twisting at the root of its mesentery, which is located in the left iliac fossa. The result is the formation of an enclosed bowel loop which becomes dilated. If untreated this can lead either to perforation due to excessive dilatation, or to ischaemia due to compromise of the blood supply.
Sigmoid volvulus - coffee bean sign
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Sigmoid volvulus - coffee bean sign
Sigmoid volvulus classically results in the formation of a loop of sigmoid colon, which is twisted at the root of the sigmoid mesentery, which lies in the left iliac fossa (LIF). The loop of dilated bowel usually points upwards towards the diaphragm.
This image demonstrates dilatation of the twisted sigmoid loop 'coffee bean' and of the proximal large bowel (*). This patient is at high risk of perforation and/or bowel ischaemia.
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Caecal volvulus
The caecum is most frequently a retroperitoneal structure, and therefore not susceptible to twisting. However, in up to 20% of individuals there is congenital incomplete peritoneal covering of the caecum with formation of a 'mobile' caecum on a mesentery, such that it no longer lies in the right iliac fossa. This is a normal variant but is associated with increased incidence of folding or twisting of the caecum (caecal volvulus), which may be complicated by obstruction, vascular compromise, or perforation.
Hover over image to show findings
Caecal volvulus
The massively dilated caecum no longer lies in the right iliac fossa (RIF). Rather this is occupied by small bowel (red outline). The small bowel is identified by the valvulae conniventes - mucosal folds that cross the full width of the bowel (arrowheads). Caecal volvulus was confirmed at laparotomy.