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2002). Leiomyomas are benign; however, they can grow to a size which can cause compression and atrophy of adjacent testicular parenchyma. Excision is curative; however, leiomyomas can occur along the entire urogenital tract. In this case, where multiple tumours were found, one should not exclude the possibility of additional tumours elsewhere along the urogenital tract. Multifocal tumours originate from a unique cellular clone


and grow multifocally within a single organ, whilst multicentric tumours do not exhibit a clonal relationship, with respect to their carcinogenesis, yet they can develop simultaneously in more than one organ (deWerra 2009). The mechanism has yet to be fully elucidated; however, when deciding appropriate treatment or surgery for tumours of paired organs it is particularly important to consider if bilateral disease represents metastasis or results from genetic predisposition. For example, human renal cell carcinoma can occur bilaterally and may be associated with a single gene alteration responsible for the development of tumours (Latif et al. 1993 and Marston Linehan 2009). An understanding of the underlying genetic predisposition allows judicious selection of a treatment protocol for the individual patient. Smooth muscle is present in the tunica albuginea,


epididymis and spermatic cord of the horse (Chacon-Arellano and Woolley 1980). Proliferations of smooth muscle can be seen in hyperplasia of the testicular smooth muscle in man (Blach et al. 2011), leiomyosarcomas in the testicular smooth muscle of horses (Allison and Moeller 1999) and leiomyomas of the testicular smooth muscle of horses (Johnson and Steinberg 1989). The macroscopic and histopathological appearance of leiomyomas is very similar to that of fibromas, although neither metastasise and excision is curative for both neoplasms. Immunohistochemistry using an antibody against alpha smooth muscle actin can be employed to identify smooth muscle (Weiermayer and Richter 2009). This is the first report of a bilateral, multicentric leiomyoma in the testes of a horse confirmed with histopathology and immunohistochemistry. This case highlights the importance of considering neoplasia as a differential for bilateral testicular masses. In this case, genetic predisposition or a simultaneous transformation event is more likely than metastasis, due to the well differentiated, encapsulated, noninvasive nature of the neoplasm.


Manufacturer’s address 1GE Healthcare, Chalfont St. Giles, Buckinghamshire, UK.


References


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Chacon-Arellano, J.T. and Woolley, D.M. (1980) Smooth muscle cells in the testicular capsule of the horse, pig and sheep. J. Anat. 131, 263-273.


Chiong, E., Tan, K.B., Siew, E., Rajwanshi, A., See, H. and Esuvaranathan, K. (2004) Uncommon benign intrascrotal tumours. Ann. Acad. Med. 33, 351-355.


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Foster, R.A., Ladds, P.W. and Hoffman, D. (1989) Testicular leiomyoma in a ram. Vet. Pathol. 26, 184-185.


Henneke, D.R., Potter, G.D., Kreider, J.L. and Yeates, B.F. (1983) Relationship between condition score, physical measurements and body fat percentage in mares. Equine. J. 15, 371-372.


Johnson, R.C. and Steinberg, H. (1989) Leiomyoma of the tunica albuginea in a horse. J. Comp. Pathol. 100, 465-468.


Latif, F., Tory, K., Gnarra, J.R., Yao, M., Duh, F.M., Orcutt, M.L., Stackhouse, T., Kuzmin, I., Modi, W. and Geil, L. (1993) Identification of von Hippel-Lindau disease tumor suppressor gene. Science 260, 1317-1320.


Mak, C., Tzeng, W., Chou, C., Chen, C., Chang, J. and Tzeng, C. (2004) Leiomyoma arising from the Tunica Albuginea of the testis: sonographic findings. J. Clin. Ultrasound 32, 309-311.


Marston Linehan, W. (2009) Genetic basis of bilateral renal cancer; Implications for evaluation and management. J. Clin. Oncol. 27, 3731-3733.


Pascoe, J.R., Ellenburg, T.V., Culbertson, M.R. Jr and Meagher, D.M. (1981) Torsion of the spermatic cord in a horse. J. Am. Vet. Med. Ass. 178, 242-245.


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Schumacher, J. (2012) Testis. In: Equine Surgery, Eds: J.A. Auer and J.A. Stick, Elsevier, St. Louis, Missouri. pp 804-838.


Skalli, O., Ropraz, P., Trzeciak, A., Benzonana, G., Gillessen, D. and Gabbiani, G. (1986) A monoclonal antibody against alpha-smooth muscle actin: a new probe for smooth muscle differentiation. J. Cell Biol. 103, 2787-2796.


Weiermayer, P. and Richter, B. (2009) Simultaneous presence of a seminoma and a leiomyoma in the testes of a horse. Equine Vet. Educ. 21, 172-176.


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