Small bowel volvulus is a rare cause of small bowel obstruction which requires rapid diagnosis and surgical intervention. Volvulus occurs when a loop of bowel twists on the axis of its own mesentery. This can then result in mechanical obstruction with or without mesenteric ischaemia and thence gangrene. The consequences can be fatal: in the elderly mortality from ischaemic necrosis can be as high as 90%.1
In the West incidence is rare; 1.5 to 5.7/1000001
with secondary volvulus accounting for 70–90% of these cases. In Africa and Asia the incidence is higher at 24 to 60/1000002
and primary volvulus accounts for most cases. Our case of a primary adult jejunal volvulus in the West is thus rare and very few published reports were found in our literature search.
Aetiology can be primary or secondary. It is thought that primary volvulus is due to a bulky food bolus in the proximal jejunum pulling the loop down, shifting other empty parts of small bowel upwards and causing the mesentery to twist. Secondary volvulus is caused by peristalsis through an obstructed bowel loop secondary to a predisposing state.
Small bowel volvulus can be difficult to diagnose because the clinical signs are those of obstruction and peritonism and, as such, are non-specific. Laboratory investigations such a leucocytosis, raised amylase, raised lactate dehydrogenase and metabolic acidosis all suggest the diagnosis, but again, are non-specific. Plain abdominal film can show dilated small bowel but will not distinguish viable from non-viable bowel, nor identify volvulus as a cause. Other imaging options such as barium studies and angiography may be more helpful. Barium studies can show the ‘corkscrew’ appearance of volvulus and angiograms the ‘barber pole’ sign from spiralling branches of twisted superior mesenteric artery. However, these modalities do not allow rapid diagnosis.
CT scanning is a widely available non-invasive mode of imaging with good diagnostic ability. The most specific sign present in 75% of small bowel volvuli is the ‘whirl’ sign, which is due to the twisting of mesentery round a point of torsion, although it is only visible when the mesenteric axis is parallel to the CT section.1
The ‘peacock tail’ sign is demonstrated when there is bowel torsion around its mesenteric axis. Both signs are diagnostic. A distended and fluid filled proximal bowel with sudden transition to a collapsed distal loop is also characteristic. At the point of transition, there may be a small bowel/faeces sign—gas and solid within dilated small bowel loops. Other signs suggestive of volvulus are signs representing a closed loop obstruction. A ‘U’ shaped configuration of distended and twisted bowel loops containing contrast, or a radial (‘spoke wheel’) arrangement of mesenteric vessels converging to a central point, are examples. In offering a sensitivity of 94–100% and specificity of 90–95%3,4
CT scanning is powerful in diagnosis and establishing causality.
Furthermore, CT imaging is invaluable for detection of small bowel ischaemia. Small bowel ischaemia is a potentially fatal complication of small bowel volvulus: mortality in non-infarcted bowel is 5–8%5
and in infarcted bowel 40–100%.6,7
Ischaemia is notoriously challenging to diagnose in that bowel enhancement can be normal, increased, decreased or even absent. However, there are other signs to look for. These are bowel wall thickening, mesenteric oedema and ascites. An early but non-specific sign of bowel oedema and inflammation is the target sign. This is where thickened bowel shows an enhanced inner and outer layer, sandwiching a middle layer of low attenuation.
The mainstay of treatment is early laparotomy with resection of non-viable bowel and primary anastomosis.
- Small bowel volvulus is a rare and life threatening cause of small bowel obstruction which requires rapid diagnosis and surgical intervention.
- CT scanning is a widely available non-invasive mode of imaging with good diagnostic ability, offering a sensitivity of 94–100% and specificity of 90–95% in establishing both the diagnosis and cause of small bowel ischaemia, and allows surgical intervention planning.
- The ‘whirl’ sign and ‘peacock tail’ sign are diagnostic of small bowel volvulus. Others are suggestive.