There are many reasons why a veterinarian may perform an ultrasound of the duodenum and jejunum sections of the small intestines in a dog or a cat.

For example, the vet may suspect a GI foreign body, inflammatory disease, or neoplasia. 

Here are a few key checkpoints to remember when scanning the duodenum and jejunum.

Setting Up the Gastrointestinal Ultrasound Study

If a patient can be fasted, that’s ideal.

An empty gastrointestinal tract may be easier to visualize, whereas food or digestive content may cause artifacts such as beam attenuation. However, this won’t be possible for all patients, especially in an emergency situation.

Patients are often placed in dorsal recumbency, although lateral recumbency may also be used. The patient can also be repositioned mid-study if needed for better visualization. 

Performing a Thorough Evaluation

Often, a GI ultrasound study is part of an entire abdominal study. In some cases, the GI tract may be visualized on its own. Either way, to ensure nothing is missed, it’s important to perform the study the same way each time. Many experts recommend keeping it simple by following the GI tract in its normal order of digestion, i.e. starting with the stomach, then moving on to the small intestines (duodenum, jejunum, ileum), cecum, and colon. Examine each segment in both longitudinal and transverse views.

Evaluation should include wall thickness (and whether that thickness remains uniform within each GI section), wall layers, luminal contents, signs of obstruction, the presence of a GI mass or multiple masses, infiltrative disease, and whether there’s normal motility/peristalsis.

The Duodenum

The duodenum is located along the right lateral abdominal wall in dogs. It can be found near (ventral to or ventrolateral to) the right kidney. The cranial portion may be challenging to see and may require viewing via an intercostal approach.

In cats, the duodenum may be closer to midline, or just right of midline.

The wall of the duodenum is up to 5mm thick in dogs, and 2-2.5mm thick in cats.

Jejunum

It’s often difficult to trace the long jejunum loop by loop. So, most veterinarians evaluate the jejunum by sweeping the transducer from side to side across the abdomen, in a cranial to caudal direction. Slightly overlapping each sweep will ensure that nothing is missed.

The wall of the jejunum is 2-5mm in dogs, and 2-2.5mm in cats. 

Evaluating the Layers of the Intestinal Walls

The walls of the intestinal tract have 5 specific layers, in this order: the luminal-mucosal interface (most interior layer), mucosa, submucosa, muscularis, and serosa (outermost layer). 

In longitudinal view, these layers are easily distinguished from one another (in a normal patient), thanks to their alternating pattern of hyper- and hypoechogenicity. The inner and outermost layers, and the submucosa, are hyperechoic. The mucosa and muscularis are hypoechoic. 

If these 5 layers are not distinctly visible throughout the intestines, it could indicate a problem. For example, focal wall thickening with obliteration of the layers could indicate focal neoplasia.

Make notes of any wall thickenings, whether they’re focal or diffuse, and whether the 5 layers are still distinguishable or not.

One normal finding that could be mistaken for abnormal is Peyer’s patches (pseudoulcers) in dogs, which appear as focal, hyperechoic indentations within the hypoechoic mucosal layer.

Signs of Obstruction

Sometimes, the obstructing foreign body may be visualized directly. However, this is often not possible. So, a foreign body obstruction may be detected due to differences in intestinal dilation proximal and distal to the point of obstruction. The intestinal tract proximal to the obstruction would tend to be dilated with fluid and gas, while the distal intestinal tract is normal or even empty.

With a linear foreign body, plication of the intestines may be seen via ultrasound. The foreign body itself may or may not be well visualized.

In case of an intussusception, the affected section of intestines will have a characteristic “bullseye” appearance in transverse view. If this is noted in an older pet, be sure to search for signs of neoplasia that could explain why the intussusception occurred.

Intestines may be hypermotile with a recent obstruction, but possibly hypomotile with a more chronic condition.

GI Neoplasia and Inflammatory Conditions

Neoplasia in the digestive tract may occur as a solitary mass, multiple masses, or diffusely as an infiltrative disease.

As mentioned above, discreet masses are often identified because of their focal thickness relative to the rest of the intestines and disruption of the wall layers.

Infiltrative disease, however, can be more difficult to pinpoint. There may be wall thickening with or without disruption of the wall layers. In particular, it can be challenging or impossible to differentiate between small cell lymphoma and inflammatory bowel disease in cats without further testing.

Regional lymph nodes should be evaluated, too.

Conclusion

The duodenum and jejunum are an important part of any GI evaluation. It’s helpful to get an idea of what’s normal and what’s not for these sections of the small intestines, as they’re commonly evaluated for a variety of conditions, including those listed above. 

Written by: Dr. Tammy Powell, DVM