Abdominal X-ray - Abnormal bowel gas pattern Volvulus
Key points
Volvulus is a specific cause of obstruction with characteristic X-ray appearances
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.
Sigmoid volvulus
The sigmoid colon is more prone to twisting than other segments of the large bowel because it is 'mobile' on its own mesentery, which arises from a fixed point in the left iliac fossa (LIF). Twisting at the root of the mesentery results in the formation of an enclosed loop of sigmoid colon which becomes very dilated. If untreated this can lead either to perforation, due to excessive dilatation, or to ischaemia due to compromise of the blood supply.
The sigmoid colon is very dilated because it is twisted at the root of its mesentery in the left iliac fossa (LIF). The proximal large bowel is also dilated (asterisks).
The twisted loop of sigmoid colon is said to resemble a coffee bean. As in this case the loop of dilated sigmoid colon - or 'coffee bean' - usually points upwards towards the diaphragm.
This patient is at high risk of perforation and/or bowel ischaemia.
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.
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.
