Being able to detect the cause of chronic vomiting in dogs and cats when renal and liver diseases have been ruled out often relies upon the aid of high resolution gastrointestinal tract sonography. To be able to diagnose changes in the gastrointestinal tract wall, surrounding lymph nodes and pancreas requires excellent resolution, sonographic technique and optimal patient factors. Excess gas in the gastrointestinal tract or obesity makes the detection of subtle changes challenging.
Recent reports have shown the importance of recognizing subtle echogenicity changes and echo patterns to diagnose inflammatory and neoplastic intestinal wall infiltrates. This may also hold true for the detection of pancreatitis in cats which tends to be more of a chronic nature than the disease in dogs. For this reason, it may be more important to recognize more subtle changes in the feline pancreas than previously thought.
Novel methods of examining the gastrointestinal tract may also become important in veterinary medicine. These include endosonographic ultrasound and computed tomography.
Gastric Causes of Chronic Vomiting
Primary gastric causes of chronic vomiting include diffuse inflammatory infiltration, neoplasia, foreign body, polyps, ulcers, pyloric hypertrophy, and delayed gastric emptying. Their diagnosis can be challenging and often requires a combination of radiography, ultrasound, and endoscopy. Thickening of the stomach wall is commonly associated with chronic vomiting and is probably one of the most commonly over-interpreted findings on survey radiographs. Because both negative and positive contrast radiographic studies of the stomach are very time consuming and can be difficult to interpret, currently, ultrasound and endoscopy are the methods of choice for imaging the stomach wall.
Ultrasonographically, thickening of the stomach wall can be characterized as focal or diffuse, concentric or asymmetric. Attention to technique is necessary since oblique scanning of the stomach wall may lead to an artificially increased thickness and disruption of wall layering.1 Therefore, scanning in multiple planes perpendicular to the stomach wall is necessary to avoid this error. Focal thickening with disrupted wall layering may be caused by neoplasia, granulomas, and ulcers. Generalized thickening is more commonly seen with inflammatory disease but can also occur with diffuse neoplastic infiltration. Thickening of the gastric wall is considered to be present when the wall thickness is greater than 5 mm in dogs and 3 mm in cats.
The gastroduodenal junction should be examined ultrasonographically in vomiting dogs. Congenital hypertrophic pyloric stenosis and chronic hypertrophic gastropathy have a similar ultrasonographic appearance. Circumferential thickening (>3 mm) of the muscularis layer can be recognized by a hypoechoic layer that appears like a ring in cross-section. In chronic hypertrophic gastritis the mucosa can also be thickened. The strong peristaltic contractions against the thickened pylorus can also be observed. These contractions fail to propel food through the pylorus and a reflux movement of the gastric contents can be seen and recorded on videotape or digital clips.
Gastric ulcers will lead to disruption of the mucosal surface and they usually cannot be diagnosed using survey radiographs alone. Their diagnosis requires a radiographic contrast study, ultrasound, or endoscopy. It is important to remember that ulceration of the stomach wall has various causes and that the stomach wall should be thoroughly investigated, preferably with ultrasound, for evidence of underlying disease. Ultrasonographically, benign ulcers appear as a localized wall thickening. Mucosal craters with an irregular surface and the adherence of gas bubbles may also be detected.2 Unfortunately, the presence of air, food, or lack of ultrasound beam penetration in large or obese dogs may make their detection difficult. Benign ulcers may appear similar to those associated with neoplasms. When the thickened stomach wall shows a loss of wall layering gastric neoplasia should be suspected.
Generalized wall thickening may be seen with a number of conditions including chronic hypertrophic gastritis, eosinophilic gastritis, fungal infiltrations, and malignant histiocytosis. Gastric wall thickening may also occur secondarily to protracted vomiting due to pancreatitis or azotemia, for example. It is not uncommon to find diffusely or multifocal thickened and rounded rugal folds. In such cases it can usually be ruled out as a primary infiltration when metabolic disease can be confirmed. Biopsy is the only way of confirming the diagnosis of gastric wall edema, however.
Both diffuse and localized gastric wall infiltrations may be detected with ultrasound, which often eliminates the need for contrast studies. Neoplasms can be recognized during abdominal ultrasound by observing thickening of the wall and the disruption of the normal wall layering, which is usually of decreased echogenicity and may create the appearance of pseudolayering.3 Also, regional lymph nodes are often enlarged. Gastric lymphoma occurs in both dogs and cats and causes a generalized, hypoechoic thickening of the stomach wall with loss of wall layering.4
Endoscopic ultrasound represents a new and alternative imaging modality for gastric lesions. High quality video endoscopes provide both optical and sonographic imaging of the gastrointestinal wall and of perigastric organs. A high frequency transducer can be placed in direct contact with the gastric wall allowing the mucosal surface of the entire stomach to be examined. Intestinal gas and obesity are no longer barriers to obtaining a high resolution image of the wall. Endoscopic ultrasound can be used in combination with conventional endoscopy to examine the gastric wall and visualize the mucosa at the same time. This technique also allows more precise targeting of mucosal biopsies to regions of the wall that are abnormal in the sonographic image. Tumor extent can be precisely described with this method when transabdominal ultrasound proves difficult.
Chronic Enteropathy Causing Vomiting and Diarrhea
The major focus of two-dimensional gray-scale ultrasound in dogs with chronic enteropathies in the past has been the description of intestinal wall thickness and layering for differentiating inflammatory from neoplastic disorders and differentiation of neoplastic from granulomatous infiltrations.5,6 Measurements of intestinal wall thickness have not been found to be specific or sensitive for diagnosis of inflammatory bowel disease in dogs.7 In addition to thickness, altered wall layering appears to be an important finding differentiating inflammatory from neoplastic and granulomatous infiltration.6,5,8 Intestinal wall thickness has been examined in dogs with enteritis.6,9 Mild wall thickening (mean 6mm) without loss of layering was found in 89% of dogs with non-specific enteritis in one study.6 Loss of layering was only seen in severe enteritis or with hemorrhagic, necrotizing or granulomatous infiltration.6 In 75 dogs with chronic non-responsive diarrhea, duodenal and jejunal wall thickening was not common and was found to be independent of body weight at thicknesses of 3-4mm and 2-3 mm, respectively.9 These findings suggest there are no significant differences in wall thickness in dogs with enteritis compared with normal dogs.10 A recent study found that dogs with inflammatory disorders, regardless of the cause or degree of clinical activity, had little if any bowel wall thickening and usually maintained normal wall layering.11 Therefore, measurements of wall thickness alone could lead to false negative results for dogs with intestinal wall inflammation.
Two different patterns of increased echogenicity have been recognized in dogs with inflammatory disorders; hyperechoic speckles and hyperechoic striations.11 A normal, hypoechoic jejunal mucosa in a dog with chronic diarrhea has a sensitivity of 80% and a specificity of 81% for the diagnosis of food responsive inflammatory disorders. The presence of hyperechoic striations in the jejunum has a sensitivity of 75% and a specificity of 96% for dogs with protein losing enteropathy. However, hyperechoic speckles in the jejunum and duodenum can be identified in all dogs with inflammatory disorders, and should be considered a less specific finding. In another study, histopathologic lacteal dilation was present in 96% of dogs with mucosal striations. Sonographic findings associated with mucosal striations included: mild jejunal wall thickening (96%), mild duodenal wall thickening (78%), mucosal speckles (70%), and abdominal effusion (87%). The mucosal striations were diffuse (70%) or multifocal (30%) and did not cause loss of wall layering.12 Mesenteric lymphadenopathy was identified in 9% of dogs. Thirteen dogs with endoscopic biopsies had mild to moderate villus lacteal dilation and the nine dogs with surgical biopsies had moderate to severe dilation. Inflammatory infiltrates were mild (61%) or moderate (30%) with variable numbers and combinations of cells, including eosinophils (65%), plasma cells (61%), lymphocytes (57%), and neutrophils (30%); one dog had disseminated villus histiocytic sarcoma. The biochemistry changes and clinical signs were consistent with protein-losing enteropathy in 78% of dogs. Hyperechoic mucosal striations in dogs are associated with lacteal dilation and are frequently associated with mucosal inflammation and protein losing enteropathy.
Intestinal wall thickness, mucosal echogenicity, lymph node morphology and mucosal histologic features do not appear to be helpful monitoring parameters in dogs with inflammatory disorders.11 Most important is the fact that diffuse intestinal neoplasia can mimic inflammatory findings sonographically and intestinal biopsy is the only definitive way of differentiating the two at this time.
Neoplastic Disease Causing Vomiting and Diarrhea
Localized mural infiltrations due to inflammation or neoplasia can slowly narrow the intestinal lumen. Some degree of intestinal dilation is present and solid foreign material such as small stones can collect proximal to the stricture. Ultrasonographically, neoplastic infiltrates produce intestinal wall thickening often with a loss of wall layering.13 Lymphoma is the most common intestinal tumor in cats but also occurs frequently in dogs. It commonly leads to either a symmetrical or asymmetrical, transmural, circumferential thickening. The wall layers are difficult to identify and the entire wall appears hypo- to anechoic. The infiltration of the intestinal wall may be solitary, diffuse, or multifocal and regional lymph nodes may be enlarged. Complete intestinal obstructions often do not occur. Another, less commonly reported, but nonetheless common appearance of lymphoma in cats is a generalized hypoechoic thickened muscular layer.
Intestinal carcinoma often produces a solitary intestinal mass as can polyps, leiomyomas, or leiomyosarcomas. Carcinomas tend to be annular, irregular infiltrations that invade the lumen and cause obstructions.14 Regional lymphadenopathy can also commonly be identified. Granulomatous infiltrations due to fungal or algal infections may also cause diffuse or focal infiltration of the bowel wall and are difficult to distinguish from neoplasia ultrasonographically.15 Histoplasmosis, for example, can produce localized and severe wall infiltrations that resemble lymphoma. Pythium causes severe thickening with loss of layering or pseudolayering and severe regional lymphadenopathy. Jejunal smooth muscle hypertrophy has been described in the cat and can also cause focal wall thickening but the wall layering is maintained.16 Because ultrasonographic appearance of the bowel wall alone is not sufficient for a definitive diagnosis, either full thickness biopsies, ultrasound-guided percutaneous biopsies, or fine-needle aspirates of the bowel wall are required for a definitive diagnosis of fungal disease.
1. Easton S. A retrospective study into the effects of operator experience on the accuracy of ultrasound in the diagnosis of gastric neoplasia in dogs. Vet Radiol Ultrasound 2001;42(1):47-50.
2. Penninck D, Matz M, Tidwell A. Ultrasonography of gastric ulceration in the dog. Veterinary Radiology & Ultrasound 1997;38(4):308-312.
3. Penninck DG, Moore AS, Gliatto J. Ultrasonography of canine gastric epithelial neoplasia. Veterinary Radiology & Ultrasound 1998;39(4):342-348.
4. Richter KP. Feline gastrointestinal lymphoma. Vet Clin North Am Small Anim Pract 2003;33(5):1083-98, vii.
5. Graham JP, Newell SM, Roberts GD, Lester NV. Ultrasonographic features of canine gastrointestinal pythiosis. Vet Radiol Ultrasound 2000;41(3):273-277.
6. Penninck D, Smyers B, Webster CR, Rand W, Moore AS. Diagnostic value of ultrasonography in differentiating enteritis from intestinal neoplasia in dogs. Vet Radiol Ultrasound 2003;44(5):570-575.
7. Rudorf H, van Schaik G, O'Brien RT, Brown PJ, Barr FJ, Hall EJ. Ultrasonographic evaluation of the thickness of the small intestinal wall in dogs with inflammatory bowel disease. J Small Anim Pract 2005;46(7):322-326.
8. Manczur F, Voros K. Gastrointestinal ultrasonography of the dog: a review of 265 cases (1996-1998). Acta Vet Hung 2000;48(1):9-21.
9. Rudorf H, van Schaik G, O'Brien RT. Ultrasonographic evaluation of the small intestinal wall thickness in dogs with inflammatory bowel disease from the UK. Vet Radiol Ultrasound 2004;in press.
10. Delaney F, O'Brien RT, Waller K. Ultrasound evaluation of small bowel thickness compared to weight in normal dogs. Vet Radiol Ultrasound 2003;44(5):577-580.
11. Gaschen L, Kircher P. Two-dimensional grayscale ultrasound and spectral Doppler waveform evaluation of dogs with chronic enteropathies. Clin Tech Small Anim Pract 2007;22(3):122-127.
12. Sutherland-Smith J, Penninck DG, Keating JH, Webster CR. Ultrasonographic intestinal hyperechoic mucosal striations in dogs are associated with lacteal dilation. Vet Radiol Ultrasound 2007;48(1):51-57.
13. Penninck D, Smyers B, Webster CR, Rand W, Moore AS. Diagnostic value of ultrasonography in differentiating enteritis from intestinal neoplasia in dogs. Vet Radiol Ultrasound 2003;44(5):570-575.
14. Paoloni MC, Penninck DG, Moore AS. Ultrasonographic and clinicopathologic findings in 21 dogs with intestinal adenocarcinoma. Veterinary Radiology & Ultrasound 2002;43(6):562-567.
15. Graham JP, Newell SM, Roberts GD, Lester NV. Ultrasonographic features of canine gastrointestinal pythiosis. Veterinary Radiology & Ultrasound 2000;41(3):273-277.
16. Diana A, Pietra M, Guglielmini C, Boari A, Bettini G, Cipone M. Ultrasonographic and pathologic features of intestinal smooth muscle hypertrophy in four cats. Vet Radiol Ultrasound 2003;44(5):566-569.