History and Clinical Findings
An 8-year-old neutered male Basset Hound was evaluated at a primary care clinic because of a 1-week history of abdominal distension, lethargy, and inappetence that had progressed to anorexia 2 days prior. The referring veterinarian suspected an abdominal mass, and the dog was referred to a veterinary teaching hospital for further diagnostic workup. During the referral examination, abdominal ultrasonography revealed a moderate amount of echogenic free fluid within the abdomen and a large, ill-defined, heterogeneous, mixed echogenic, irregularly marginated mass with cavitated regions that occupied most of the abdomen. The liver was cranially displaced and contained multifocal, well-defined, hypoechoic to mixed echogenic, irregularly marginated nodules up to 2.5 cm in diameter. Some of the lesions were targetoid, with a hypoechoic center and isoechoic rim. Similar lesions were also present within the head of the spleen; the tail of the spleen was not visualized. Left inguinal lymph nodes were rounded and hypoechoic. Abdominocentesis was performed, and fine-needle aspirate specimens of the abdominal mass, liver, and sternal lymph nodes were collected. Abdominal fluid smears (direct and cytocentrifuged) were prepared for examination, and hemorrhagic effusion with moderate neutrophilic inflammation was detected. The results of these and other performed tests were discussed with the owner, and because of its poor prognosis, the dog was euthanized by means of IV injection of pentobarbital sodium and phenytoin sodium solution.
Gross Findings
At necropsy, the abdomen contained approximately 400 mL of serosanguineous fluid with white wispy flocculent material. More than 70% of the abdomen was occupied by a 14 × 21 × 29 - cm, tan to red to black, multinodular mass, which was adhered to and had disrupted the spleen and was intertwined with the mesentery (Figure 1). It contained umbilicated nodules, firm nodules, and softer, cavitated nodules that exuded a clear brown-tinged fluid from cut surfaces. The spleen was diffusely mottled dark purple to black and had rounded edges; the serosal surface was uneven with multifocal, white, raised nodules that extended into the parenchyma. The largest nodule measured 0.5 × 2.0 × 3.0 cm. The liver had well-defined, multifocal, white to yellow firm nodules (some with depressed centers) that were pinpoint to 5 cm in diameter. The overlying omentum, right lateral body wall, diaphragm, and serosal surface of the urinary bladder contained multifocal to coalescing raised white nodules that were pinpoint to 1 cm in diameter. The mediastinal, mesenteric, and sublumbar lymph nodes were enlarged.
Photographs of a 14 × 21 × 29-cm, tan to red to black, multinodular mass that occupied > 70% of the abdomen of a dog that had a 1-week history of abdominal distension, lethargy, and inappetence that had progressed to anorexia 2 days prior. The mass was adhered to and had disrupted the spleen and was intertwined with the mesentery. Bar = 7.5 cm. Inset—The liver contained multiple metastatic nodules of the splenic mass. Bar = 3 cm.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1113
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page→
Cytologic and Histopathologic Findings
Cytologic examination of sections of the splenic mass revealed low cellularity with moderate hemodilution. There were few large oval to spindle-shaped mesenchymal cells that appeared mostly individualized and rarely organized in small aggregates. The cells had round to oval, central nuclei, with finely stippled chromatin and prominent nucleoli that varied in number and size and basophilic cytoplasm with variable numbers of small clear vacuoles (Figure 2). The cells had a moderate nuclear-to-cytoplasmic ratio and moderate to marked anisocytosis and anisokaryosis. Abundant extracellular eosinophilic matrix was present in the background, and marked windrowing of erythrocytes was also apparent. Examination of fine-needle aspirate specimens of the liver and sternal lymph nodes revealed atypical mesenchymal cells with the same cytologic appearance as those observed in the splenic tissue and abundant amorphous to fibrillar eosinophilic material in the background. A cytologic diagnosis of sarcoma was made, and histologic assessment of tissue samples was requested for further classification of the neoplasm.
Tissue samples were routinely processed and stained with H&E stain for histologic examination. The splenic mass was an unencapsulated, poorly demarcated, infiltrative, moderately cellular neoplasm composed of polygonal to spindle-shaped cells arranged in streaming bundles within myxoid background. The neoplastic cells were surrounded by irregular islands and thick trabeculae of abundant, variably basophilic, chondromatous matrix and cartilage (Figure 3), which often contained lacunae with single to multiple neoplastic cells (Figure 4). Neoplastic cells had indistinct cell borders, moderate amounts of eosinophilic cytoplasm, and round to oval nuclei with stippled chromatin and a small nucleolus. The mitotic index was 7 mitotic figures/10 hpfs (40X objective). The stroma contained multiple necrotic areas. There was multiple vascular invasion by the neoplastic cells. In less affected areas of spleen, there was moderate congestion with hemorrhage. Similar neoplastic lesions were seen in the samples of the diaphragm, liver, mesentery, abdominal wall, serosal surface of the urinary bladder, and lymph nodes (mediastinal, mesenteric, and sublumbar).
Photomicrograph of a fine-needle aspirate specimen from the splenic mass in the dog in Figure 1. The sample contains ovoid to spindle-shaped mesenchymal cells. The round nuclei have finely stippled chromatin and multiple prominent nucleoli; the basophilic cytoplasm contains few small distinct vacuoles. Abundant extracellular eosinophilic matrix is evident in the background. Modified Wright-Giemsa stain; bar = 20 μm.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1113
Photomicrograph of a section of the splenic mass in the dog in Figure 1. Tissue of the spleen has been replaced by a neoplasm composed of polygonal to spindle cells surrounded by irregular islands and thick trabeculae of abundant, variably basophilic, chondromatous matrix and cartilage. H&E stain; bar = 2.5 mm.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1113
Morphologic Diagnosis and Case Summary
Morphologic diagnosis and case summary: splenic extraskeletal chondrosarcoma with disseminated metastasis to the diaphragm, kidneys, liver, mesentery, abdominal wall, urinary bladder, and lymph nodes (mediastinal, mesenteric, and sublumbar) in a dog.
Photomicrograph of a section of the splenic mass in the dog in Figure 1. Neoplastic cells are embedded in myxomatous and chondromatous matrix and have indistinct cell borders, moderate amounts of eosinophilic cytoplasm, and round to oval nuclei with stippled chromatin and a small nucleolus. Notice that lacunae often contain 2 or more neoplastic cells. H&E; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1113
Comments
Chondrosarcoma is a rare tumor that typically develops from skeletal cartilage. Chondrosarcoma accounts for approximately 10% of bone tumors in medium- and large-breed dogs, and flat bones are more often affected than long bones.1 In dogs, chondrosarcoma is a slow-growing malignant neoplasm. Affected dogs have a relatively longer survival time, compared with dogs with osteosarcomas.1,2 With treatment, the median survival time for dogs with skeletal chondrosarcoma varies from 0.9 to 6 years, depending upon the location and histologic grade of the primary tumor.2 Extraskeletal chondrosarcoma in humans, first documented by Stout and Verner,3 is characterized by formation of the neoplasm in soft tissue without preexisting cartilage, such as in the extremities.4 The case described in the present report was consistent with extraskeletal chondrosarcoma given the location of the tumor, histologic features of the neoplasm, and absence of primary skeletal chondrosarcoma. In dogs, extraskeletal chondrosarcomas in various organs including the lungs, omentum, pericardium, and heart have been reported.5,6 For the dog of the present report, the spleen was suggested to be the primary site of the neoplasm, given that the abdomen was occupied by a large mass that expanded from the spleen and there was no evidence of a primary skeletal neoplasm in pre-existing cartilage or bone. Canine extraskeletal chondrosarcoma originating from the spleen is extremely rare with only a single case7 reported, to our knowledge. The other differential diagnoses for splenic mesenchymal neoplasms (primary or metastatic) include hemangiosarcoma, leiomyosarcoma, fibrosarcoma, osteosarcoma, hemangioma, or myelolipoma; with the exception of chondrosarcoma, all can be ruled out on the basis of the morphology of the neoplastic cells and production of chondromatous matrix and cartilage.
Chondrosarcoma is histologically classified into 2 types. Myxoid chondrosarcoma is well circumscribed with a multilobular pattern and composed of spindle-shaped cells separated by variable amounts of mucoid matrix.8 Mesenchymal chondrosarcoma is composed of undifferentiated mesenchymal cells arranged in sheets with moderately to well-differentiated chondroid tissue.9 In the dog of the present report, the neoplasm was characterized by spindle cells within myxoid background with irregular islands of cartilage, which is compatible with myxoid chondrosarcoma.
Although the source of the neoplasm in the case described in the present report could not be determined, it may have originated from an undifferentiated cell in the connective tissue that subsequently differentiated into cartilage. Hisaoka and Hashimoto10 suggested that interstitial collagen types I, III, and VI and vimentin found in various samples of connective tissue may be associated with the derivation of extraskeletal chondrosarcoma. Fibroblast metaplasia or neural crest cells are also potential origins of this type of neoplasm.11
Local invasion and metastasis have been associated with chondrosarcoma.5,12 The neoplasm in the dog of the present report metastasized to multiple organs in the abdominal cavity. A mediastinal lymph node was replaced by the metastatic neoplasm, indicating that the neoplasm also had undergone lymphatic or hematogenous metastasis. The heart and lungs are common organs for metastasis of extraskeletal chondrosarcoma1; however, this dog had no metastasis in the thoracic cavity except for the mediastinal lymph node. In humans, the prognosis associated with extraskeletal chondrosarcoma is better than that associated with conventional chondrosarcoma.13 Although extraskeletal chondrosarcomas in dogs are reported to typically metastasize or undergo multicentric tumor growth,14 the metastatic rate of extraskeletal chondrosarcomas in dogs and prognosis for dogs with this type of neoplasm have not been fully investigated or reported.
Acknowledgments
Supported by European Regional Development Fund, European Social Fund, and the State Budget of the Czech Republic (project FNUSA-ICRC No. CZ.1.05/1.1.00/02.0123 to R. H.).
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