History

An 11-year-old spayed female Border Collie mix was referred for a 2-month history of abdominal discomfort, lethargy, and intermittent vomiting. Hematemesis and melena were also observed over the 24 hours prior to admission. Previous treatment included a bland diet, famotidine, doxycycline, prednisone, azathioprine, metoclopramide, and sucralfate. No clinical improvement was appreciated.

Abnormalities found on physical examination included mild lethargy, a palpable mass in the cranioventral portion of the abdomen, and slight enlargement of the submandibular lymph nodes. The CBC revealed an inflammatory leukogram, microcytic normochromic anemia, and thrombocytosis. Serum biochemical analysis revealed high alanine transaminase and alkaline phosphatase activities and high SUN concentration; the dog also had hyperglycemia, hypoalbuminemia, hyponatremia, hypokalemia, and hypochloridemia. Abdominal radiographs were obtained (Figure 1).

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Right lateral (A) and ventrodorsal (B) radiographic views of the abdomen of an 11-year-old spayed female Border Collie mix evaluated for a 2-month history of abdominal discomfort, lethargy, and intermittent vomiting.

Citation: Journal of the American Veterinary Medical Association 236, 5; 10.2460/javma.236.5.513

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

Diagnostic Imaging Findings and Interpretation

The liver appears enlarged. A fluid or soft tissue opacity, which has a dorsal margin that is incompletely viewed, overlaps the caudoventral margin of the liver. Within or overlying the mass is a tubular, curved structure containing gas and mineral. The fluid or soft tissue mass is thought to be a dilated segment of small intestine that is summated with the ventral portion of the spleen. The tubular structure may represent a focal small intestinal lesion that is causing obstruction (Figure 2).

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Same radiographic views as in Figure 1. On the lateral view, notice the summated ventral margins of the dilated small intestinal mass and spleen (white arrows) and mineralization within the tubular structure (black arrow). On the ventrodorsal view, mineralization within the mass is evident (black arrow).

Citation: Journal of the American Veterinary Medical Association 236, 5; 10.2460/javma.236.5.513

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A large heterogenous small intestinal mural mass is evident on abdominal ultrasonography within the left middle portion of the abdomen. The mass appears to be causing a partial small intestinal obstruction (Figure 3). The mass is irregularly marginated with a small component extending beyond the mural margins. Mineralization is observed with acoustic shadowing. On the basis of the findings of abdominal radiography and ultrasonography, the diagnosis is mineralized small intestinal mass, likely neoplastic, with partial obstruction. Differential diagnoses for a mineralized abdominal mass arising from the small intestinal wall include neoplasia (eg, adenocarcinoma, leiomyosarcoma, and lymphoma), inflammatory reaction (abscess or granuloma), hyperplasia, calcified hematoma, and heterotopic mesenteric ossification.^1,2

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Transverse ultrasonographic images of the abdominal mass of the same dog as in Figure 1. A and B—Orad to the mass, notice the dilated small intestine with irregular mucosa (arrows). C—Mineralization is detected within the mass (vertical arrow) with acoustic shadowing distal to the mineralization (horizontal arrows).

Citation: Journal of the American Veterinary Medical Association 236, 5; 10.2460/javma.236.5.513

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Comments

Resection and anastomosis of the distal portion of the jejunum was performed to remove the mass. Splenectomy, liver biopsy, and mesenteric lymph node biopsy were also performed. Histopathologic diagnoses included an extraskeletal osteosarcoma (most likely primary as no skeletal tumor was identified), hepatocellular degeneration consistent with steroid hepatopathy, and splenic necrosis. There was no evidence of metastasis to the lungs or lymph node. The dog was treated with carboplatin and doxorubicin and was monitored for metastasis and bone marrow suppression. Seven months after diagnosis, the dog had ultrasonographic and cytologic evidence of hepatic metastasis and subsequently died at home.

Extraskeletal osteosarcomas are malignant mesenchymal tumors that produce osteoid without being associated with bone. Extraskeletal osteosarcomas in dogs are uncommon, accounting for only 0.13% of biopsy submissions in 1 study,³ and result in different clinical signs than their skeletal counterparts. Dogs with internal extraskeletal osteosarcomas often have vague clinical signs such as depression and lethargy or abdominal distension.³ Metastasis to the liver, spleen, local lymph nodes, and lungs have all been reported, and extensive local infiltration is common.¹

On radiographic images, extraskeletal osteosarcomas classically appear as irregular soft tissue masses with diffuse or focal mineralization without nearby bone involvement.⁴ Abdominal ultrasonography is valuable because it allows assessment of the tumor's effects on nearby structures, evaluation of common sites of metastasis, and some evaluation of tumor morphology. Although findings on abdominal radiographs can indicate intestinal obstruction, abdominal ultrasonography is more sensitive for detection of gross metastasis and local tumor effects on the small intestine. Histologic examination of biopsy specimens is necessary to confirm the diagnosis. Thoracic computed tomography may be more sensitive in detecting neoplastic foci than conventional radiography.