- Case Study
- Case Discussion
Figures 1 and 2:
Sagittal(Figure 1) and transverse (Figure 2) images of the descending colon. The colon wall is greatly thickened, and layered detail is not seen(closed arrows). The mucosal surface is seen as a hyperechoic, reflective interface with acoustic shadowing (open arrows).
Sagittal image of the descending colon at the transition from the proximal, normal colon wall (closed arrow) to the thickened wall segment that had altered layering (open arrow).
An eleven-year-old neutered male Domestic Shorthair cat was presented with a four-month history of persistent diarrhea and weight loss. He had a normal appetite. A trial of metronidazole had been prescribed, but the owner had not been successful in administering the drug. Prior to the history of diarrhea, the cat had a chronic history of constipation.
Physical examination was normal. No obvious abdominal masses were palpated, and his abdomen did not appear painful. A complete blood count, blood chemistry profile and total T4 level were normal with the exception of a mildly elevated globulin level.
Abdominal radiographs were unremarkable. Abdominal ultrasound revealed a focal region of circumferentially thickened colon wall which did not have the normal, layered appearance (See Figures 1, 2 and 3). The ileocecal colonic junction was localized and was normal. Thoracic radiographs were done to assess for pulmonary metastatic lesions, and they were normal. An ultrasound-guided fine-needle aspirate of the thickened colon wall was obtained and cytology was nondiagnostic.
An exploratory laparotomy was performed and the abnormal region of colon was surgically excised. Histopathology revealed severe, focally extensive, lymphoplasmacytic and pyogranulomatous colitis. The underlying etiology of this inflammation was uncertain. The surgical margins revealed only low numbers of inflammatory cells. The cat recovered uneventfully from surgery. Chronic therapy for inflammatory bowel disease was planned if clinical signs persisted or recurred, but they did not.
Clinical Presentation of Gastrointestinal Disease
The clinical signs of diarrhea and weight loss are nonspecific and can be due to primary or secondary gastrointestinal (GI) disease. Examples of secondary GI disease seen in cats include renal and hepatic disease, diabetic ketoacidosis, hyperthyroidism, pancreatitis, drug therapy, toxin exposure and non-gastrointestinal neoplasia. Most of these conditions can be ruled out with a complete history, physical examination, complete blood count, blood chemistry profile, urinalysis, total T4, feline pancreatic lipase immunoreactivity (fPLI) level and radiography.
Examples of primary GI disease seen in cats include infectious and noninfectious inflammatory disease, neoplasia and intraluminal foreign bodies. These diseases are usually ruled out with fecal tests for infectious disease, radiography, ultrasonography, endoscopy, surgery and biopsy. Survey abdominal radiographs may identify an abdominal mass, but localization to the GI tract, or a specific region of the GI tract, is often not possible. Contrast radiographs can be done to help localize the lesion, but this procedure can be stressful to the cat, time consuming to the staff, and involves exposure of both to ionizing radiation. Oral administration of contrast agent can also result in vomiting and aspiration in animals with GI disease. Endoscopy requires general anesthesia, and evaluation is limited to the mucosal surface of the regions of the GI tract that are ‘reachable’ with the scope. Exploratory laparotomy is a valid approach to the diagnosis of GI disease, but it is usually optimal to have a tentative diagnosis prior to surgery.
Abdominal Ultrasound and GI Disease
Abdominal ultrasound has more recently become a valuable method to evaluate animals suspected of having primary GI disease. That being said, operator experience plays an important role in the sensitivity of this imaging method to detect GI lesions. Abdominal ultrasound is non-invasive, rapid, can be done repeatedly to monitor progression or response to therapy. With ultrasound one can evaluate bowel wall layering, thickness and motility, can determine the location of a lesion, and can assess for intraabdominal metastases. Intraluminal gas and ingesta frequently interfere with GI ultrasound, but with effort and experience, these factors are not always obstacles.
The layers of the GI wall in the stomach, small intestine and colon are all somewhat similar in appearance in the stomach, small intestine and colon. The layers are seen as alternating hyperechoic andhypoechoic bands, and consist of a hyperechoic mucosal surface, hypoechoic mucosa, hyperechoic submucosa, hypoechoic muscularis and hyperechoic serosa (see Figures 4 and 5). Gastrointestinal wall thickness is measured from the mucosalsurface/mucosa interface to the far edge of the serosa. Normal feline stomach and small intestinal wall thickness ranges from 2.0 to 3.2 mm, and normal colon wall thickness is usually between 1.4 and 1.7 mm. Normal canine GI wall thicknesses are: stomach, 3 to 5 mm; duodenum, 5.1 to 6 mm; jejunum, 4.1 to 4.7 mm and colon, 2 to 3 mm.
The inner mucosal surface is frequently associated with intraluminal gas, and therefore is commonly seen as a hyperechoic reflective interface with incomplete acoustic shadowing. Identification of this interface in the center of an abdominal mass during an ultrasound exam suggests that the mass involves the GI wall (see Figures 1 and 2). Imaging the transitional region where a normal wall and an abnormal, thick wall are continuous also assists in localizing a lesion to the GI tract (See Figure 3). To localize the specific region of GI tract involved, landmarks and/or the appearance of the intestine can be assessed. The stomach is located in the cranial left abdomen. Rugal folds are observed when it is not fully distended. The duodenum is located along the right ventral abdomen. The region of the ileocecal-colonic junction is usually medial to the right kidney, and it has a unique appearance in the cat (click here to go to feline ileum description and images). The colon wall can beidentified as it is typically thinner than the small intestinal wall, and its mucosal surface often has a prominent, crescent-shaped, hyperechoic reflective interface which has an incomplete ‘dirty’ acoustic shadow. The descending colon can also be identified by its sagittal orientation along the left lateral abdomen.
Infiltrative intestinal disease can present ultrasonographically in a variety of ways, and there is a large amount of overlap between the differential diagnoses of ultrasound findings. In general, loss of GI layering is more commonly associated with neoplasia, and normal layering is more commonly associated with inflammatory disease. This cat in the above case study illustrates that there are exceptions to this generalization.
Ultrasound-guided fine-needle aspiration or biopsy (PowerPoint file) of GI lesions is safe and can provide useful information. In general, lesions smaller than 2 cm are aspirated, and lesions larger than 2 cm are biopsied if the fine needle aspirate is nondiagnostic. Penetration of the GI lumen should be avoided. The accuracy of ultrasound-guided aspirates and biopsies vs. biopsies obtained by surgery or necropsy has been reported to be approximately 70%. Benign vs. malignant disease cannot be distinguished 100% of the time. Correlation to the clinical presentation is always important. Endoscopic or surgical biopsies may be indicated if results of an ultrasound-guided fine needle aspirate or biopsy are inconclusive or the diagnosis does not make sense clinically.
In this cat, an ultrasound-guided fine needle aspirate was done to rule out lymphosarcoma. If lymphosarcoma was definitively diagnosed, chemotherapy would have been offered without surgery as there was no evidence of obstruction. Since the fine needle aspirate was nondiagnostic, surgical excision of the mass was done. Prognosis and therapy indicated was determined based on the histopathology results.
- Baez JL Hendrick MJ, Walker LM, Washabau RJ: Radiographic, ultrasonographic, and endoscopic findings in cats with inflammatory bowel disease of the stomach and small intestine: 33 cases (1990-1997), J Am Vet Med Assoc 21:349-354, 1999.
- Crystal MA Penninck DG, Matz ME, Pearson SH, Freden GO, Jakowski RM: Use of ultrasound-guided fine-needle aspiration biopsy and automated core biopsy for the diagnosis of gastrointestinal diseases in small animals, Vet Radiol Ultrasound 34(6):438-444, 1993.
- Delaney F, O’Brien RT, Waller K: Ultrasound evaluation of small bowel thickness compared to weight in normal dogs, Vet Radiol Ultrasound 44(5):577-580, 2003.
- 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 42(1):47-50, 2001.
- Goggin JM Biller DS, Debey BM, Pickar JG, Mason D: Ultrasonographic measurement of gastrointestinal wall thickness and the ultrasonographic appearance of the ileocolic region in healthy cats, J Am Anim Hosp Assoc 36:224-228, 2000.
- Grooters AM Biller DS, Ward H, Miyabayashi T, Couto CG: Ultrasonographic appearance of feline alimentary lymphoma, Vet Radiol Ultrasound 35(6):468-472, 1994.
- Hall EJ, German AJ: Disease of the small intestine, Textbook of Veterinary Internal Medicine, ed 6, Ettinger SJ, Feldman EC (eds), St. Louis, Elsevier Saunders:1332-1378, 2005.
- Mattoon JS, Auld DM, Nyland TG: Abdominal ultrasound scanning techniques, Small Animal Diagnostic Ultrasound, ed 2, Nyland TG, Mattoon JS (eds): Philadelphia, WB Saunders Co: 49-91, 2002
- Milner RJ Peyton J, Cooke K et al: Response rates and survival times for cats with lymphoma treated with the University of Wisconsin-Madison chemotherapy protocol: 38 cases (1996-2003), Am Vet Med Assoc 227:1118-1122, 2005.
- Myers NC, Penninck DG: Ultrasonographic diagnosis of gastrointestinal smooth muscle tumors in the dog, Vet Radiol Ultrasound 35(5):391-397, 1994.
- Newell SM Graham JP, Roberts GD, Ginn PE, Harrison JM: Sonography of the normal feline gastrointestinal tract, Vet Radiol Ultrasound 40(1):40-43, 1999.
- Paoloni MC, Pennick DG, Moore AS: Ultrasonographic and clincopathologic findings in 21 dogs with intestinal adenocarcinoma, Vet Radiol Ultrasound 43(6):562-567, 2002.
- Pennick DG: Gastrointestinal tract, Small Animal Diagnostic Ultrasound, ed 2, Nyland TG, Mattoon JS (eds): Philadelphia, WB Saunders Co: 207-230, 2002.
- Pennick DG: Ultrasonography of alimentary lymphosarcoma in the cat, Vet Radiol Ultrasound 35(4):299-304, 1994.
- Pennick DG Smyers B, Webster CRL, Rand W, Moore AS: Diagnostic value of ultrasonography in differentiating enteritis from intestinal neoplasia in dogs, Vet Radiol Ultrasound 44(5):570-575, 2003.
- Penninck DG Crystal MA, Matz ME, Pearson SH: The technique of percutaneous ultrasound guided fine-needle aspiration biopsy and automated microcore biopsy in small animal gastrointestinal diseases, Vet Radiol Ultrasound 34(6):433-436, 1993.
- Steiner JM: Diarrhea, Textbook of Veterinary Internal Medicine, ed 6, Ettinger SJ, Feldman EC (eds), St. Louis, Elsevier Saunders:137-140, 2005.
- Swann HM, Holt DE: Canine gastric adenocarcinoma and leiomyosarcoma: A retrospective study of 21 cases (1986-1999), J AM Anim Hosp Assoc 38:157-164, 2002.
- Twedt DC, Vomiting: Textbook of Veterinary Internal Medicine, ed 6, Ettinger SJ, Feldman EC (eds), St. Louis, Elsevier Saunders:132-136, 2005.
- Washabau RJ, Holt DE: Diseases of the large intestine, Textbook of Veterinary Internal Medicine, ed 6, Ettinger SJ, Feldman EC (eds), St. Louis, Elsevier Saunders:1378-1408, 2005.