Imaging the small bowel

Dr John P Wright

Updated: 5 May 2008

The most robust, reliable, hidden and enigmatic part of the gastrointestinal tract must be the small bowel. Unlike the stomach and colon the small bowel has adequate spare capacity in case of disaster and it seldom complains. It has a very low risk of growing nasty malignancies and has a whole intricate system for maintaining cleanliness as apposed to many of our other tubular structures.

Investigation of the small bowel has traditionally been a case of smoke and mirrors. We measure various substances made by the mucosa to assess its condition and we use X rays and/or magnetic resonance, and contrast to get an impression of its anatomy.

To actually examine the mucosa we have two options. We can pass (i.e. shove) an endoscope down from the mouth or up from the anus. This is a bit like using a garden hose to unblock a drain under the house, possible, but unpleasant, and time consuming. The alternative is capsule video endoscopy. This is a painless procedure that enables direct visualization of the small bowel mucosa but without the possibility of biopsy. There is still some debate as to whether an endoscopy of the small bowel is preferable to a capsule examination. This is a sterile debate. Capsule endoscopy is the preferred diagnostic procedure while endoscopy offers an interventional opportunity. It is similar to the use of X ray or ultrasound prior to laparoscopic or surgical procedure.

These modalities are therefore complementary and their use depends on the clinical problem. Before examining the small bowel the upper gastrointestinal tract and the terminal ileum need to be adequately examined and the duodenal, ileal and colonic mucosa need to be biopsied. Depending on the situation, other factors such as gastrointestinal infections, drug effects and a multitude of other causes need to be considered before imaging is undertaken. Given this proviso’s three situations will be discussed:

Obscure gastrointestinal bleeding and/or iron deficiency anaemia

Before imaging the small bowel a second set of endoscopies with biopsy as indicated above is usually indicated. A second endoscopist may be appropriate in some situations. If the gastrointestinal bleeding is massive urgent angiography will be needed. If this is negative or the bleeding occult, a capsule video endoscopy is then indicated. Positive findings may require small bowel endoscopy, angiography with embolization or abdominal surgery. Negative capsule endoscopy may be followed by simple observation and iron replacement or further investigation such as a Meckel’s scan. The use of isotope scans for quantifying blood loss or identifying bleeding sources are now second line investigations after the above process has failed. In patients with iron deficiency anaemia it is normal practice after a negative capsule endoscopy to treat with oral or intravenous iron until ferritin is normal and then to observe over a 3 month period before planning further procedures.

Suspected small bowel Crohn’s Disease

First line investigation is a colonoscopy with biopsy of ileum and, right and left colon. If an obstructive disease is suspected by the presence of abdominal cramps rather than diarrhoea and possibly the lack of an inflammatory response, capsule endoscopy is contraindicated. In this situation a 64-channel CAT scan with oral and possible intravenous contrast is the examination of choice. Conversely when mucosa inflammation is suspected and the acute phase reactants increased a capsule video endoscopy is indicated.

Of interest is the entity of indeterminate colitis. These patients are generally thought to follow a pattern of Crohn's Disease as time goes on. As the medical treatment of Crohn's disease and ulcerative colitis is increasingly similar this differentiation is seldom critical in the clinical setting. The problem however arises when it comes to surgery and the creation of an ileal pouch. The development of pouchitis in these patients often leads to patients needing standard therapy for Crohn's disease including the use of anti TNF antibodies. It is therefore suggested that patients with total colitis should undergo capsule video endoscopy to pick up those with Crohn's of the small bowel earlier rather than later. This will also permit the earlier use of biological drugs which have now been shown to fundamentally modify the disease process.

Chronic watery diarrhoea of uncertain etiology

Once again upper and lower gastrointestinal endoscopy with duodenal, ileal and colonic biopsy is the first line approach. If inflammatory bowel disease is found in the colon no further small bowel investigation may be needed. However if microscopic colitis and particularly collagenous colitis is found coeliac disease may be an associated condition. If villous atrophy or blunting is found further examination of the small bowel is needed. At this point controversy intervenes around the diagnosing of coeliac disease.

Serological tests, tissue transglutaminase and anti-endomysial antibodies, are available. Initially thought to be very sensitive time has shown this not to be the case. In a study published this March about 10% of patients with histological coeliac (Marsh grade 3 or higher) had negative serology at diagnosis. Even more interesting is the 44% of patients who after a year of a gluten free diet still have diarrhoea, flat villi and negative serology. This study used duodenal biopsy as the “gold standard” but increasingly coeliac disease is being diagnosed without diagnostic flat duodenal villi. The debate as to whether the mucosa can be involved in a patchy way is still contentious but is finding increasing support from video capsule endoscopists.

In conclusion investigation of the small bowel has improved radically over the past few years but the costs have increased as well. With a capsule video endoscopy costing about R10 000.00, a CAT scan of the abdomen with contrast R5 500.00 and a 2 hour double balloon endoscopy in theatre R6 000.00 some medical aids are balking at these costs. As with most expensive modern techniques the indications for the procedures, the cost of missing a diagnosis, as well as the cost of making a diagnosis needs to be evaluated. Not least the skill of the operator and the accuracy of the preliminary investigations such as endoscopy and histology need to be added into the decision tree. It is however apparent that the new techniques are a major step forward in diagnosing small bowel conditions.