Abdominal X-ray - Abnormal bowel gas pattern Small bowel obstruction/ileus
Key points
Dilated small bowel >3cm is considered abnormal
Small bowel obstruction and ileus can have similar appearances
If a patient presents with clinical features of obstruction then radiological assessment can be very helpful in determining the level of obstruction, and occasionally the cause.
There are features visible on a plain abdominal X-ray that may help locate the level of obstruction. These are partly determined by a knowledge of small and large bowel anatomy. See the page on normal Bowel Gas Pattern.
Dilatation >3cm of the small bowel is considered abnormal, however the longer the segment of bowel that is dilated, the more likely bowel dilatation represents a genuine obstruction.
Centrally located multiple dilated loops of gas filled bowel (arrowheads)
Valvulae conniventes (arrow) are visible - confirming this is small bowel
Evidence of previous surgery - note the anastomosis site (red ring) - this suggests adhesions is the likely cause of obstruction (confirmed at surgery)
Small bowel obstruction - causes
The most common causes of obstruction are adhesions secondary to intra-abdominal surgery, hernias, tumours and Crohn's disease. Regardless of whether there is evidence of these causes on an abdominal radiograph, a full surgical history should be taken and examination of the hernial orifices should be performed.
Ileus
Ileus is a term used for aperistaltic bowel not caused by a mechanical obstruction. This phenomenon is common after abdominal surgery. The radiological features can be similar to those of obstruction.
Appearances are similar to those of mechanical obstruction
There are multiple loops of gas filled bowel projected centrally over the abdomen
This patient had prolonged non-colicky abdominal pain following a Caesarean section - recovery was spontaneous
Sentinel loop
Intra-abdominal inflammation, such as with pancreatitis, can lead to a localized ileus. This may appear as a single loop of dilated bowel known as a 'sentinel loop.'
