Top tips for scanning for small bowel disease

By Dr Ruth Reeve, Clinical Specialist GI Sonographer, Portsmouth Hospitals University NHS Trust

1. Check the patient history and talk to the patient to understand their symptoms – Consider what surgery the patient may have had previously – this may mean that the anatomy is not in a normal location. Check if the patient has had a recent endoscopy investigation, this helps when putting together the endoscopic and radiological findings. Consider the patients’ symptoms (pain, bowel habit etc) and what the biochemistry is (Calprotectin, CRP etc), this will give you an idea if there is likely to be active disease and potential complications.

2. Choose your tools - Having a variety of transducers available is helpful when assessing the small bowel. By using a low or mid-range frequency transducer you can get a good overview of anatomy and views of deeper structures. A high frequency probe is usually the best method for undertaking a detailed assessment of the small bowel for signs of inflammation.

3. Wall appearances - Ultrasound appearances of the wall are the biggest indicators of small bowel disease; this involves looking at the thickness and appearance of the wall stratification. Wall thickness over 3mm is highly suggestive of inflammation, the appearance and predominance of the stratification can indicate the type of inflammation (acute or chronic). Using Doppler to assess the wall of the small bowel can help assess for signs of active inflammation.

4. Mesentery – Secondary signs of inflammation are important to identify during assessment of small bowel disease. Lymphadenopathy can aid confidence in calling acute inflammation but are not specific to certain small bowel diseases. Mesenteric hypertrophy or fat wrapping is a pathognomonic feature of Crohn’s disease. Fat wrapping is seen when the mesentery expands around the circumference of the intestine, so called “creeping fat”. Inflammation tends to involve the mesenteric border of the affected loop of bowel, assessing for changes in the appearance of the mesentery can also indicate the stage of inflammation.

5. Look for complications - Possible complications of Crohn’s disease that may be assessed on ultrasound include: fistulating disease, abscess formations, stenosis, bowel obstruction and perforation. Fistula, abscess and perforation may look like complex collections containing fluid and gas with fistulous tracts communicating with the small bowel lumen. Stenoses are defined as segments of thickened stiff bowel wall with luminal narrowing (<1cm) with proximal luminal dilation (>3cm) with hyperperistalsis of the pre-stenotic gut.