Shoulder Mass in a Dog
Sonographer: Anne Desrochers DVM DACVIM
Age: 6 years
Gender: Neutered Male
Breed: Boston Terrier
Patient presented for a grade 2/5 RF lameness and pain on extension of the right shoulder. Pet was treated with Carprofen 25mg daily for two weeks without significant clinical improvement. On subsequent evaluation, a firm mass was palpated on the dorsal aspect of the scapula.
Right Thoracic Limb Radiographs Interpretation:
A poorly defined area of mineral opacity was visualized within the most proximal portion of the right scapula.
A well-defined mixed echogenicity mass was seen adjacent to the dorsal aspect of the scapula measuring at least 2.4x2.5x2.6cm. The mass contained a few hyperechoic areas casting strong acoustic shadows consistent with mineralization and a few small anechoic fluid-filled cavitated regions. Vascular signal was obtained when assessing the mass with color flow Doppler. The hyperechoic bone echo of the dorsal aspect of the scapula adjacent to the mass was slightly irregular. Ultrasound evaluation of the abdomen and thoracic cavities was unremarkable.
Ultrasound-guided fine-needle biopsies of the mass were obtained under light sedation.
Suspect chondrosarcoma. The cytologic findings were most suggestive of a chondrosarcoma; 70% confidence. However, other differentials such as a chondroma or a chondroblastic osteosarcoma were also possible. Biopsy/histopathology was required to obtain a definitive diagnosis. Photo: few suspected chondroblasts surrounded by numerous windrowing red blood cells and abundant extracellular pink matrix.
A subtotal right scapulectomy was performed to resect the mass and 8 cm of the most dorsal portion of the scapula.
Findings were consistent with a well differentiated chondrosarcoma which appeared completely excised.
Chondrosarcoma is a malignant neoplasm accounting for 5%-10% of all primary bone tumors reported in dogs. The tumor can develop in the nasal cavity (highly susceptible), ribs, pelvis, vertebrae, facial bones, appendicular skeleton and extraskeletal sites such as mammary gland, heart, valves, aorta, larynx, trachea and penis. Chodrosarcoma generally does not metastasize rapidly but when it does common sites may include the lungs, kidney, liver, heart and skeleton. The metastatic rate in dogs is about 20%. Medium to large breeds like Boxers, German Shepherds and Golden Retrievers are at an increased risk and the disease is most frequently reported in middle aged to older dogs. No sex predilection has been reported so far. Chondrosarcoma is amenable to surgery because a reliable adjuvant chemotherapeutic agent does not exist for this type of cancer. Although it is resistant to radiation therapy, there have been reports where responses to coarse-fraction radiation protocols were achieved. Prognosis in dogs treated with amputation showed a median survival of 540 days. Death is mostly reported in case of metastatic disease.
Consultation with an oncologist to provide additional diagnostic and therapeutic advice was recommended but not pursued. Pet recovered uneventfully from surgery and is progressing well in his rehabilitation program.
Sonographer: Anne Desrochers, DVM DACVIM
Special thanks to Dr. Knode and the staff at House Paws Round Hill for their help with this case.