What Is Your Diagnosis?

Chase E. Constant Center for Veterinary Health Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078.

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Holly D. Polf Center for Veterinary Health Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078.

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History

An approximately 1-year-old 22.7-kg (50-lb) castrated male Australian Shepherd mix was evaluated because of a 2-day history of vomiting, lethargy, and anorexia. A mass associated with the mesentery at the ileocecal junction was excised at the time of neutering 5 months earlier. Histologic examination of the mass revealed steatitis and granulomatous inflammation; no neoplastic cells were found. This mass was suspected to have been induced by abdominal trauma or peritonitis. The patient recovered uneventfully from surgery.

On initial evaluation, the patient was febrile (40.22°C [104.4°F]) and lethargic and appeared uncomfortable and a firm mass was palpated in its midabdominal region. No other abnormalities were identified on physical examination or hematologic evaluation. Abdominal radiographs were obtained (Figure 1).

Figure 1—
Figure 1—

Right lateral (A) and ventrodorsal (B) radiographic views of the cranial portion of the abdomen of an approximately 1-year-old Australian Shepherd mix evaluated because of an acute onset of vomiting and a palpable abdominal mass.

Citation: Journal of the American Veterinary Medical Association 246, 1; 10.2460/javma.246.1.51

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page

Diagnostic Imaging Findings and Interpretation

A poorly defined soft tissue mass is evident in the midventral aspect of the abdomen to the right of midline with a superimposed irregular gas opacity and small superimposed mineral opacities (Figure 2). The mass is displacing the small intestine cranially, caudally, and to the left of midline. Some segments of the small intestine are gas distended, measuring > 2 times the height of the body of L5, and some segments of the small intestine appear normal in diameter. Several of the gas-distended loops of small intestine have an atypical distribution; they are arranged in linear segments, one on top of the other, rather than a normal relaxed bending arrangement. An incidental finding of a separate center of ossification of the os penis is evident. The mass in the midventral aspect of the abdomen could be originating from the intestinal tract or mesentery. Differential diagnoses included granuloma, abscess, recurrence of the previous inflammatory mesenteric mass, neoplasia, or intestinal adhesions. A mechanical ileus was suspected secondary to the mass.

Figure 2—
Figure 2—

The same radiographic images as in Figure 1. A large soft tissue mass (arrows) with a superimposed irregular gas opacity (asterisk) is evident. Notice the gas dilated segments of the small intestine, some of which have an atypical distribution (arrowheads).

Citation: Journal of the American Veterinary Medical Association 246, 1; 10.2460/javma.246.1.51

Abdominal ultrasonography was performed, which revealed a large multilobulated mass lesion homogenously hypoechoic to the surrounding mesentery with visible small intestine within the mass lesion (Figure 3). The mucosal and submucosal layers of the affected small intestine were visible, suggesting that wall layering was intact but the definitive origin of the mass (a small intestine wall mass vs a mesenteric mass with secondary incarceration of small intestine) could not be determined. Several loops of small intestine that were not within the mass were severely dilated with fluid and had reduced peristalsis. Given these results, the mass was determined to be of mesenteric or small intestinal origin. A small intestinal obstruction was also confirmed.

Figure 3—
Figure 3—

Longitudinal ultrasonographic image of the cranial portion of the abdomen of the same dog as in Figure 1. Notice the large, fairly homogenously hypoechoic mass (asterisk) with a closely associated segment of small intestine (arrow). Notice that the normal hypoechoic mucosal and normal hyperechoic submucosal layers of the intestine are visible (arrowhead). Image was obtained via a transabdominal approach with a 3- to 9-MHz micro-convex array transducer. Scale to the right of image indicates depth in centimeters.

Citation: Journal of the American Veterinary Medical Association 246, 1; 10.2460/javma.246.1.51

Treatment and Outcome

Fine-needle aspiration of the mass did not yield a sufficient quantity of cells to make a definitive diagnosis. The dog underwent exploratory abdominal surgery, and the mass was excised. The mass was adhered to several loops of jejunum and extended down to the origin of the cranial mesenteric artery. A portion of jejunum and ileum was resected. The patient recovered uneventfully from surgery and did well following discharge from the hospital. Ultrasonographic examination of the abdomen was repeated 10 weeks after surgery and revealed no evidence of tumor regrowth.

Histologic evaluation and immunohistochemical analysis were performed, and the mass was determined to be a leiomyosarcoma (smooth muscle actin positive, desmin positive, and c-kit [CD117] negative).1 No neoplastic cells were found in the resected portions of small intestine. These findings in addition to the surgical findings strongly suggest the tumor was mesenteric in origin; however, intestinal origin could not be completely ruled out.

Comments

Although histologic evaluation of the mass was required for a definitive diagnosis, the diagnostic imaging findings, specifically the ultrasonographic findings, refined the potential differential diagnoses and confirmed an intestinal obstruction prompting exploratory surgery. The ultrasonographic characteristics of common gastrointestinal neoplasms in dogs have been described,2,3 and the mass lesion of the case described in this report had the ultrasonographic characteristics of a leiomyosarcoma, which corresponded to the histopathologic diagnosis. Leiomyosarcomas are often large (> 3 cm) solid masses with hypoechoic or anechoic cavities, which may represent areas of necrosis or degeneration. They are frequently eccentrically associated with the lumen of the intestine. Their large size when initially detected is likely the result of the lack of clinical signs during the initial growth of the tumor and can inhibit assessment of the site and intestinal layer of tumor origin.2,3

Gastrointestinal lymphosarcoma ultrasonographically appears as a diffuse transmural thickening with a loss of normal wall layering and reduced wall echogenicity. Gastrointestinal lymphosarcoma lacks cystic cavitations and is generally associated with mesenteric lymphadenopathy.2 Intestinal carcinomas appear similar to lymphosarcoma, except they tend to involve a shorter, single segment of intestine and often cause mechanical ileus.2 This is in contrast to leiomyosarcomas, which tend to be eccentric or extraluminal focal mass lesions.2 Unlike intestinal lymphosarcoma or carcinoma, leiomyosarcoma is rarely associated with regional lymphadenopathy.3 It has also been reported that a mass involving the cecum is more likely to be a leiomyosarcoma than a carcinoma.1

Leiomyosarcoma is a slow-growing, malignant tumor of smooth muscle and is the second most common intestinal tumor and most common intestinal sarcoma in dogs.1,4 The reported median age of onset is > 10 years of age,4 with no reports to our knowledge in dogs < 5.5 years old. Clinical signs include anorexia, vomiting, diarrhea, or weight loss. Radiographic findings include an abdominal mass or evidence of peritonitis.1,4 Unlike intestinal leiomyosarcoma, primary mesenteric leiomyosarcoma is rare and, to our knowledge, there is only 1 reported case of primary mesenteric leiomyosarcoma in a dog.5

  • 1. Liptak JM, Forrest LJ. Soft tissue sarcomas. In: Withrow and Macewen's small animal clinical oncology. 4th ed. St Louis: Saunders, 2007;425454.

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  • 2. Penninck D. Gastrointestinal tract. In: Penninck D, d'Anjou MA. Atlas of small animal ultrasonography. Ames, Iowa: Blackwell, 2008;281318.

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  • 3. Meyers NC, Penninck DG. Ultrasonographic diagnosis of gastrointestinal smooth muscle tumors in the dog. Vet Radiol Ultrasound 1994; 35:391397.

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  • 4. Cohen M, Post GS, Wright JC. Gastrointestinal leiomyosarcoma in 14 dogs. J Vet Intern Med 2003; 17:107110.

  • 5. Vérine H, Chrzanowska M, Botev S. Notes on the spontaneous pathology of laboratory dogs. I. Leiomyosarcoma of the mesentery in a bitch. Bull Acad Vet Fr 1968; 41:2528.

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  • Figure 1—

    Right lateral (A) and ventrodorsal (B) radiographic views of the cranial portion of the abdomen of an approximately 1-year-old Australian Shepherd mix evaluated because of an acute onset of vomiting and a palpable abdominal mass.

  • Figure 2—

    The same radiographic images as in Figure 1. A large soft tissue mass (arrows) with a superimposed irregular gas opacity (asterisk) is evident. Notice the gas dilated segments of the small intestine, some of which have an atypical distribution (arrowheads).

  • Figure 3—

    Longitudinal ultrasonographic image of the cranial portion of the abdomen of the same dog as in Figure 1. Notice the large, fairly homogenously hypoechoic mass (asterisk) with a closely associated segment of small intestine (arrow). Notice that the normal hypoechoic mucosal and normal hyperechoic submucosal layers of the intestine are visible (arrowhead). Image was obtained via a transabdominal approach with a 3- to 9-MHz micro-convex array transducer. Scale to the right of image indicates depth in centimeters.

  • 1. Liptak JM, Forrest LJ. Soft tissue sarcomas. In: Withrow and Macewen's small animal clinical oncology. 4th ed. St Louis: Saunders, 2007;425454.

    • Search Google Scholar
    • Export Citation
  • 2. Penninck D. Gastrointestinal tract. In: Penninck D, d'Anjou MA. Atlas of small animal ultrasonography. Ames, Iowa: Blackwell, 2008;281318.

    • Search Google Scholar
    • Export Citation
  • 3. Meyers NC, Penninck DG. Ultrasonographic diagnosis of gastrointestinal smooth muscle tumors in the dog. Vet Radiol Ultrasound 1994; 35:391397.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Cohen M, Post GS, Wright JC. Gastrointestinal leiomyosarcoma in 14 dogs. J Vet Intern Med 2003; 17:107110.

  • 5. Vérine H, Chrzanowska M, Botev S. Notes on the spontaneous pathology of laboratory dogs. I. Leiomyosarcoma of the mesentery in a bitch. Bull Acad Vet Fr 1968; 41:2528.

    • Search Google Scholar
    • Export Citation

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