What Is Your Diagnosis?

Blake E. Hildreth III Department of Veterinary Clinical Sciences, College of Veterinary Medicine and Department of Cancer Biology and Genetics, College of Medicine, The Ohio State University, Columbus, OH 43210.

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 DVM, PhD
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Stephen J. Birchard Department of Veterinary Clinical Sciences, College of Veterinary Medicine.

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Thomas J. Rosol Department of Veterinary Biosciences, College of Veterinary Medicine.

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Wm Tod Drost Department of Veterinary Clinical Sciences, College of Veterinary Medicine.

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History

An 8-year-old 49.0-kg (108.0-lb) castrated male Golden Retriever was referred for evaluation of a slow-growing mass overlying the caudolateral aspect of the left elbow joint. The mass was first noticed 3 months earlier; however, the dog had no clinical signs of discomfort. One week prior to referral, the referring veterinarian obtained a fine-needle aspirate of the mass; cytologic evaluation revealed mesenchymal neoplasia.

Physical examination revealed a 7.5 × 6 × 7-cm firm and firmly fixed subcutaneous mass on the caudolateral aspect of the left elbow joint. No other physical, gait, or musculoskeletal abnormalities were detected. Findings on CBC and serum biochemical analysis were unremarkable. No abnormalities were found on 3-view thoracic radiography. Orthogonal radiographs of the left elbow joint were made (Figure 1).

Figure 1—
Figure 1—

Craniocaudal (A) and mediolateral (B) radiographic views of the left elbow joint of an 8-year-old 49.0-kg (108.0-lb) castrated male Golden Retriever that was referred for evaluation of a slow-growing mass overlying the caudolateral aspect of the left elbow joint. The mass was first noticed 3 months earlier.

Citation: Journal of the American Veterinary Medical Association 251, 6; 10.2460/javma.251.6.647

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

Diagnostic Imaging Findings and Interpretation

An extracapsular soft tissue mass is present caudolateral to the left distal aspect of the humerus and elbow joint that extends distally over the proximal portion of the antebrachium (Figure 2). Multifocal punctate and amorphous mineralized foci are present within the mass. There is no periosteal reaction or bone destruction on the adjacent humerus, radius, or ulna.

Figure 2—
Figure 2—

Same radiographic images as in Figure 1. An extracapsular soft tissue mass is present caudolateral to the left distal aspect of the humerus and elbow joint that extends distally over the proximal portion of the antebrachium. Multifocal punctate and amorphous mineralized foci are present within the mass (white arrows). No periosteal reaction or osseous destruction is evident on the adjacent humerus, radius, or ulna.

Citation: Journal of the American Veterinary Medical Association 251, 6; 10.2460/javma.251.6.647

Computed tomography of the left forelimb was performed to more extensively evaluate the mass and confirm the absence of humeral, radial, or ulnar involvement. A well-marginated, 6.6 × 5.8 × 4.4-cm soft tissue–attenuating mass containing amorphous, irregular mineral-attenuating regions was evident (Figure 3). There was peripheral rim enhancement of the mass following IV administration of contrast medium (iohexol [240 mg of I/mL]; 2.2 mL/kg [1 mL/lb]).a A lack of skeletal involvement suggested an extraskeletal origin to the mass.

Figure 3—
Figure 3—

Precontrast (A) and postcontrast (B) transverse CT images of the left elbow joint of the dog in Figure 1. A—In the precontrast image, a well-marginated, 6.6 × 5.8 × 4.4-cm soft tissue–attenuating mass that contains amorphous, irregular mineral-attenuating regions (white arrows) is evident caudolateral to the left distal aspect of the humerus and elbow joint (bone window; window width, 1,500 Hounsfield units [HU]; window length, 300 HU). B—In the postcontrast image, peripheral rim enhancement (white arrows) is evident (soft tissue window; window width, 325 HU; window length, 10 HU).

Citation: Journal of the American Veterinary Medical Association 251, 6; 10.2460/javma.251.6.647

On the basis of these findings, differential diagnoses include mesenchymal neoplasia (chondrosarcoma, osteosarcoma, histiocytic sarcoma, synovial cell sarcoma, rhabdomyosarcoma, fibrosarcoma, hemangiosarcoma, peripheral nerve sheath tumor) or nonmesenchymal neoplasia (lymphoma, carcinoma) with neoplastic mineralization. Benign differential diagnoses are synovial osteochondromatosis, chondroma, hemangiopericytoma, calcinosis circumscripta, myositis ossificans, hematoma, granuloma, or abscess, with physiologic or dystrophic mineralization or both.

Treatment and Outcome

A diagnosis of extraskeletal mesenchymal chondrosarcoma was made on the basis of histologic findings on evaluation of a preoperative biopsy sample.

Regional excision of the mass and biopsy tracts was elected. Blunt and sharp dissection was used to separate the well-demarcated mass from the subcutis. The deep margin of the mass was excised off the lateral brachial and antebrachial fascia overlying the left elbow joint and musculature. To minimize the chance of local and disseminated recurrence, radiation therapy was discussed, but not elected.

The dog was brought to the referring veterinarian 8 months later with left-sided superficial cervical lymphadenopathy, but no evidence of local recurrence on physical examination. Because of the suspicion that the lymphadenopathy resulted from metastasis, euthanasia was elected with no further diagnostic testing.

Comments

Extraskeletal chondrosarcomas represent 2% of all human and up to 13% of all canine chondrosarcomas, often arising in tissues lacking cartilage.1,2 In dogs, both males (83%) and Golden Retrievers (17%) are overrepresented.3 Although there are 3 main histologically and clinically distinct subtypes of skeletal chondrosarcomas—conventional, myxoid, and mesenchymal—only myxoid and mesenchymal extraskeletal subtypes exist.1 In people, extraskeletal mesenchymal chondrosarcomas most commonly afflict the brain, meninges, and soft tissues of the lower extremities.4 However, in dogs, isolated cases affecting intrathoracic (right atrium, pericardium, and lungs) or intra-abdominal (omentum, spleen, and retroperitoneum) structures have been documented.3,5 The overall prognosis in dogs has been poor in these isolated case reports. However, this may result from many of these affected dogs being examined when they have advanced disease (eg, clinical signs of distress caused by large intrathoracic and intra-abdominal tumors and possible metastasis).

To our knowledge, the imaging features of extraskeletal mesenchymal chondrosarcoma have not been documented for animals. Radiography is a key first diagnostic step in people to determine tumor margins, type of mineralization (if any), and bone involvement. Extraskeletal mesenchymal chondrosarcomas appear radiographically as a soft tissue mass, where in people they are described as having chondroid-type mineralizations.6 These radiographic findings correspond with their pathognomonic bimorphic histologic pattern, which was also observed histologically in the dog of the present report. Islands of differentiating chondrocytes are surrounded by a rim of mineralized extracellular matrix within sheets of undifferentiated round or spindle-shaped mesenchymal cells.1,6 This progression of cartilage differentiation resembles growth plate chondrogenesis. The centers on radiographic imaging approach, or are of similar opacity as, soft tissue, which corresponds to less dense cartilage, compared with their mineralized periphery.6 Central, but not peripheral, mineralization is found in 50% to 100% of tumors in a stippled, arc, ring, or coarse pattern and is unique to the mesenchymal subtype.6–8

Computed tomography is more sensitive for documenting the type and extent of mineralization, compared with radiography, in people with extraskeletal mesenchymal chondrosarcomas.6,8 This results from the known advantages of CT, compared with radiography, which includes the ability to display anatomic structures without anatomic superimposition, a larger gray scale, the ability to use both bone and soft tissue windows for display, and the availability of contrast enhancement. This was evident for the dog of the present report; the islands of cartilage differentiation surrounded by a rim of mineralization were even more distinct on CT images. The soft tissue component of extraskeletal mesenchymal chondrosarcomas is of similar density to skeletal muscle, and there is peripheral enhancement after IV administration of contrast medium, both features that were found for the dog of the present report.6,8 In total, imaging findings in the present report clearly distinguished the tumor from other types of sarcoma, myositis ossificans, and most importantly the other subtype of extraskeletal chondrosarcoma, the myxoid variant.1,7

In people, many extraskeletal mesenchymal chondrosarcomas are resistant to chemotherapy and radiation therapy; therefore, surgery is the preferred treatment. For the dog of the present report, a marginal juxtacapsular excision rather than forelimb amputation was chosen because of a lack of bone involvement. Our intent was to preserve limb function and follow surgery with radiation therapy.

This report documents the diagnosis of an extraskeletal mesenchymal chondrosarcoma, which had characteristic histologic and imaging features of this tumor type in people. Findings in the present report suggested that surgery alone may not be curative in dogs and the prognosis may be guarded because of the potential for metastasis.5

Footnotes

a.

Omnipaque (Iohexol 240), GE Healthcare, Chicago, Ill.

References

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