Imaging Intestinal Obstruction

Small intestinal obstruction from foreign material, masses, and intussusceptions is a common cause of vomiting.¹ Recognizing radiographic and ultrasonographic signs is necessary for correct diagnosis.^2,3

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A backup of ingesta proximal to the obstruction site can cause bowel distention (See Figures 2–6). Complete and some chronic partial obstructions can cause significant bowel dilation, and often the colon is empty. Depending on the obstruction site, the segment of bowel distention may be short or long. Compared with the small intestine, the colon is typically larger in diameter and contains fecal material. Differentiating small intestine from colon is crucial for accurate diagnosis: mistaking colon for small intestine can lead to incorrect diagnosis of small bowel obstruction, while mistaking distended small intestine for colon can lead to a missed diagnosis of small intestinal obstruction (Figure 6). Both lateral and ventrodorsal views are essential for accurate assessment, although both may not be presented in this collection.

Ultrasonography is often used to assess vomiting and can reliably diagnose small bowel obstruction.^4-6 Compared with radiography, ultrasonography can identify underlying causes more frequently.^4-6 Challenges include the presence of bowel gas (hiding foreign material), ultrasonographer experience, relatively small field of vision, and differentiation of small intestine from colon.

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Overlap exists between normal (See Figure 1) and obstructive bowel diameter.⁴ Proximal obstructions can have a short segment of duodenal distention, and distal obstructions can have longer segments of small intestinal distention. Recognizing mixed populations of normal and distended bowel is common in small intestinal obstruction. The small intestine should contain only homogeneous soft tissue opacity (fluid, liquid ingesta) and/or gas. Heterogeneous material (often feces-like) is a sign of potential obstruction from foreign material or inhibition of passage of normal ingesta.

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1. Normal Small Intestinal Diameter, Contents, & Distribution

Figure 1B, In cats, normal small intestinal diameter (between white arrows) is considered ≤1.2 cm from serosal to serosal surface.⁷

2. Foreign Body Small Intestinal Obstructions

3. Inconclusive Radiographs & Definitive Ultrasound Images

Masses associated with small intestine may result in mechanical obstruction with typical signs of bowel dilation and abnormal luminal content. A mass not apparent on radiography may be diagnosed using ultrasonography.

4. Intussusception Causing Small Bowel Obstruction

Invagination of 1 portion of the GI tract (intussuscep­tum) into the lumen of another (intus­suscipiens); this is often referred to as the target sign when seen in the transverse plane because of the multiple layers of adjacent intestinal walls.  

5. Linear Foreign Body Obstructions 

Linear foreign material often causes small bowel bunching, plication, or corrugation with or without severe intestinal dilation. String foreign bodies, more common in cats, can cause plication and/or corrugation, often without severe dilation. In dogs, cloth foreign bodies are more common and obstruction is often severe.

Lateral (Figure 5A) and ventrodorsal (Figure 5B) abdominal radiographs of a cat with string foreign body. Note the plicated (ie, ribbon candy) shape of small intestinal segments, bunched centrally. Pockets of triangular and odd-shaped abnormal intraluminal gas are present, common with linear foreign bodies.          

Figure 5D, Intestinal plication (arrows) may be seen via ultrasound; in some cases, linear foreign material (arrowheads) may be visible within the small intestinal lumen.

 


6. Differentiating Small Intestine from Colon

This older cat presented for vomiting; ultrasonography was the first diagnostic modality.

Figure 6A, Ultrasound image of an enlarged intestine (arrows) showing large amount of reverberation artifact (arrowheads) caused by luminal gas. This prohibits visualization of the far wall of this loop of bowel. The ultrasound impression was a distended colon.

LINDA LANG, DVM, is a first-year radiology resident at Washington State University. Her clinical interests include ultrasonography and computed tomography. She completed a diagnostic imaging internship at Texas Gulf Coast Veterinary Specialists in Houston, Texas, before starting her residency. Dr. Lang earned her DVM from Texas A&M University before spending 6 years in general practice in Texas.

JOHN MATTOON, DVM, DACVR, is professor of radiology at Washington State University and course director of the NAVC Institute’s Small Animal Abdominal Ultrasound course. His current research focus is clinical applications of all diagnostic imaging modalities. He is a frequent author and speaker at national and international meetings and is currently completing the third edition of Veterinary Diagnostic Ultrasound.

JENNIFER WHITE, BVSc, is a radiology resident at Washington State University. Dr. White worked in general practice in Chicago before completing a small animal rotating medicine and surgery internship at VCA Aurora/Berwyn and working overnight emergency for 1 year. She earned her veterinary degree from Massey University in Palmerston North, New Zealand.