Introduction to Abdominal Radiography

Large Bowel Dilatation

Background :

Dilated large bowel can occur either due an obstruction in the bowel or due to an ileus or pseudo obstruction. When the bowel is obstructed, for example due to a tumour, the bowel proximal to the tumour will be dilated and the distal bowel will be collapsed. If the ileocaecal valve between small and large bowel is incompetent then the small bowel will also become dilated. If there is pseudoobstruction or ileus the whole of the bowel may be dilated. Imaging may necessary to differentiate between true obstruction and ileus/pseudo-obstruction.

Diagnosis can be made by :

      Abdominal radiograph
      Computerised Tomography (CT)
      
A water soluble enema may be used to determine if there is obstruction or pseudoobstruction (contrast is passed into the large bowel to try to identify the site of the obstruction).

What to look for (radiological findings) :

Multiple loops of dilated bowel. To differentiate between large and small bowel dilatation look for the following:

This image shows dilated transverse colon. The haustra do not cross the lumen of the bowel. Faeces is seen in the caecum.  

annotate haustra    >>>       

Discussion :

It is difficult to determine the cause of large bowel dilatation from a plain radiograph. If further imaging is needed a CT scan or a water soluble enema can be performed to determine if the diagnosis is obstruction or pseudoobstruction. Further imaging will help to determine the level of the obstruction and in the case of CT can give extra information about surrounding structures.

Causes of Obstructed Bowel :

The bowel can be obstructed due to a bowel wall lesion, an obstruction in the lumen or an extrinsic abnormality. The commonest cause is a bowel tumour.

Bowel tumour - often in the sigmoid colon
Inflammation of the bowel wall in diseases such as diverticulitis, ulcerative colitis, crohns disease
Volvulous
Extrinsic compression from a pelvis mass

plus others

Causes of Ileus :