August 2013 Case of the Month

Interpretation

Sarcoma, likely chondrosarcoma

Explanation

The sample contains a homogeneous population of pleomorphic mesenchymal cells embedded in various matrices. There is no evidence of inflammation in the specimen. The cells were predominantly fusiform is shape with cytoplasmic margins that were sharply defined by the abundant amount of matrix in the background. Nuclei were large, ovoid and had fine chromatin. Anisocytosis and anisokaryosis were moderate to marked. The cellular features of the neoplastic cells warrant a diagnosis of sarcoma. The magenta extracellular material is most consistent with either chondroid or osteoid. Fibrin tends to stain less magenta and is slightly more fibrillar in appearance. The basophilic material is most consistent with either mucus or a myxoid component i.e. glycosaminoglycans (Question 1). A mucus component could be part of the neoplastic process (but this is seen in epithelial-derived tumors and not sarcomas). Alternatively, the mucus could also be present from the oral cavity. Sarcomas frequently have areas that differentiate to produce different types of matrix, which can make diagnosis of these tumors challenging on cytology and small biopsies. Given the cytologic diagnosis of a sarcoma and the abundant magenta matrix, leading differential diagnoses initially included a chondrosarcoma or an osteosarcoma. A chondrosarcoma was favored due to the cellular features of the mesenchymal cells, the lakes of matrix with embedded cells (the matrix in osteosarcomas tend to be less abundant and tumor cells are not usually embedded in the matrix but rather surround it) and the location of the tumor in the epiglottis.

Further information and follow-up

A biopsy of the mass was submitted for histopathologic analysis and a diagnosis of a myxoid chondrosarcoma was made. The dog in this case went home with the owners and is currently not undergoing treatment for this tumor.

Discussion

Laryngeal neoplasms are considered rare in dogs. When they do occur, tumors can arise from the cartilaginous tissue (chondromas or chondrosarcomas), skeletal muscle (rhabdomyoma or rhabdomyosarcoma) or the overlying epithelium (carcinomas). Oncocytomas are a neoplastic proliferation of round cells rich in mitochondria that also can occur in laryngeal tissue (Question 2). Many tumors originally thought to be oncocytomas were later classified as being of muscle origin and the actual cellular origin of these tumors remains an area of debate.^1-5 In chondromas, areas of endochondral ossification have been reported and some have argued that these lesions should be considered dysplastic rather than neoplastic.¹ The majority of reported tumors in this region or not biologically aggressive in terms of metastasis, but local destruction of the laryngeal tissue can be clinically problematic.⁶ The cells in this case had clear mesenchymal cell differentiation and abundant amounts of matrix. Chondromas consist of monomorphic chondrocytes that display minimal nuclear atypia. The cells in this neoplasm displayed marked anisokaryosis and moderate anisocytosis, favoring a diagnosis of chondrosarcoma. Primary chondrosarcomas arise from existing normal cartilage located in the pelvis, nasal cavity, sternum, ribs and less often the long bone. Chondrosarcomas arising in extraskeletal locations are generally considered to be not as aggressive as their skeletal counterparts. This is true in dogs and people. However, metastasis of these tumors has been reported.⁷ In dogs, extraskeletal chondrosarcomas have been reported in the lung, omentum, heart and pericardium, spleen, abdomen, retroperitoneum, and liver.^8-12 Wide surgical excision is generally thought to improve survival time. However, the infrequency with which this tumor is seen in this location complicates prognostication and the surgery can be exceedingly difficult.¹³ Rare cases of successful surgical management have been reported in the literature.¹⁴

References

1. Meuten DJ, ed. Tumors in Domestic Animals, 4th Edition, Iowa State Press, Ames, Iowa, USA, 2002, pp 287-289.
2. Wheeldon, E. B., Suter, P. F. & Jenkins, T. Neoplasia of the larynx in the dog. 1982. J Am Vet Med Assoc. 180: 642-647.
3. Flanders, J. A., Castleman, W., Carberry, C. A. & Tseng, F. S. Laryngeal chondrosarcoma in a dog. 1987. J Am Vet Med Assoc. 190: 68-70.
4. Meuten, D. J., Calderwood-Mays, M. B., Dillman, R. C., Cooper, B. J., Valentine, B. A., Kuhajda, F. P. & Pass, D. A. Canine laryngeal rhabdomyoma. 1985. Vet Pathol. 22: 533-5398.
5. Pass D.A., Huxtable C.R., Cooper B.J., Watson A.D.J., and Thompson R., Canine Laryngeal Oncocytomas. 1980. Vet Pathol. 17: 672-677.
6. Patnaik, A. K. Canine extraskeletal osteosarcoma and chondrosarcoma: a clinicopathologic study of 14 cases. 1990. Vet. Pathol. 27: 46–55.5.
7. Daisuke Kojima, Hitoshi Hatai, Toshifumi Oyamda and Chun-Ho Park. Extraskeletal Myxoid Chondrosarcoma with Systemic Metastasis in a Five-Month-Old Irish Setter Dog. 2012. J. Vet. Med. Sci. 74: 1045–1049.
8. Albers, T. M., Alroy, J., Garrod, A., Brown, D. and Penninck,D. Histochemical and ultrastructural characterization of primary cardiac chondrosarcoma. 1997. Vet. Pathol. 34: 150–151.
9. Chikata, S., Nakamura, S., Katayama, R., Yanagisawa, S., Matsuo, Y., Yamane, I. and Takahashi, K. Primary chondrosarcoma in the liver of a dog .2006. Vet. Pathol. 43: 1033–1036.
10. Greenlee, P. G. and Liu, S. K. Chondrosarcoma of the mitral leaflet in a dog. 1984. Vet. Pathol. 21: 540–542.
11. Miller, J. M., Walshaw, R. and Bourque, A. C. Primary splenic mesenchymal chondrosarcoma in a dog. 2005. Can. Vet. J. 46: 163–165.
12. Munday, J. S. and Prahl, A. Retroperitoneal extraskeletal mesenchymal chondrosarcoma in a dog. 2002. J. Vet. Diagn. Invest. 14: 498–500.
13. Waltman, S. S., Seguin, B., Cooper, B. J. & Kent, M. Clinical outcome of non nasal chondrosarcoma in dogs: thirty-one cases (1986–2003). 2007. Vet Surg. 36: 266-271.
14. Muraro L, Aprea F, White RA. Successful management of an arytenoid chondrosarcoma in a dog. 2013. J Small Anim Pract. 54(1):33-35.