EQUINE VETERINARY EDUCATION / AE / MARCH 2015


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Case Report Bilateral leiomyoma in the testes of a horse


A. L. Stoll, R. Tucker*†, T. H. Witte† and K. C. Smith Department of Pathology and Pathogen Biology and †Clinical Science and Services, Royal Veterinary College, University of London, Hatfield, Hertfordshire, UK. *Corresponding author email: rtucker@rvc.ac.uk


Keywords: horse; tumours; neoplasia; immunohistochemistry; tunica albuginea


Summary A 19-year-old Hackney pony was referred to a veterinary teaching hospital for further investigation of left-sided scrotal enlargement. Both testes were normally positioned within the scrotum and there was no pain on palpation. Ultrasonography revealed multiple masses of soft tissue echogenicity, located adjacent to the testicular parenchyma. They were hyperechoic when compared to the testicular parenchyma and affected both testes. Surgical excision was performed by closed castration. Gross examination revealed firm, white, nodular masses of varying size on the surface of both testes. The cut surface of individual masses had a dense, whorling, fibrous and somewhat shiny appearance. The histopathological diagnosis was bilateral, multicentric, well differentiated leiomyoma of the tunica albuginea. The smooth muscle origin was confirmed by immunohistochemical staining with an anti-human monoclonal antibody reactive to smooth muscle actin. This is the first report of a bilateral, multicentric, leiomyoma in the testes of a horse confirmed by histopathology and immunohistochemistry. This case highlights that neoplasia should be considered as a differential for bilateral testicular enlargement.


Introduction


The incidence of testicular tumours in horses is considered rare and early castration is commonplace, but reported tumours include those of germ cell, sex cord stromal cell, mixed and other cell origins (Schumacher 1999). Bilateral testicular tumours have been reported in horses and include bilateral seminoma (Christensen et al. 2007), leiomyosarcoma (Chiong et al. 2004) and a mixed seminoma and leiomyoma (Weiermayer and Richter 2009). Testicular neoplasia often presents as nonpainful enlargement of scrotal testes (Brinsko 1998). The most common tumour of equine testes is the seminoma, a germ cell tumour, which can grow quickly and has the potential to metastasise (Brinsko 1998), highlighting the importance of early diagnosis and treatment. Leydig and Sertoli cell tumours are less common in horses. Leydig (also known as interstitial) cell tumours are more common in cryptorchid testes (Edwards 2008). Neoplasia of the testes must be differentiated from a number of other pathological conditions of the scrotal contents which can be nonpainful (hydrocoele and haematocoele) or painful (orchitis, periorchitis, torsion of the spermatic cord, inguinal herniation and testicular abscess) (Pascoe et al. 1981 and Brinsko 1998).


Case history


A 19-year-old Hackney pony was referred to a veterinary teaching hospital for further investigation of left-sided scrotal


enlargement. The owner had noted the enlargement for approximately 3 weeks. It was uncertain how large the testes were at the time the abnormality was first noted or how long they had definitively been enlarged. The pony was not in use as a breeding animal although had served mares on a few occasions as a younger animal. No behavioural changes had been observed and there was no history of weight loss or colic.


Clinical, gross and histopathological findings and treatment


On physical examination the animal was in good general health. Vital parameters were within normal reference ranges and body condition score was graded 5/9 (Henneke et al. 1983).


Both testes were normally positioned within the scrotum. An approximately 10 cm diameter firm mass was palpated adjacent to, and adhered to, the left testicle. This mass had reportedly enlarged since the initial examination 3 weeks previously. Several smaller sized masses were palpable adjacent to the right testicle. These were of the same consistency as the mass on the left testicle and were also adhered to the testicle. The right testicle had not been noted as abnormal previously. The scrotal skin had a normal appearance and was freely movable over the testes. There was no pain on palpation with no heat or further swelling. No other urogenital abnormalities were identified. Ultrasonography of the testes was performed in the


standing unsedated horse (Vivid 7 8–10 MHz linear array)1.An extra-testicular echogenic mass of soft tissue echogenicity was identified adjacent to the pampiniform plexus of the left testicle. The structure had a similar echogenicity throughout, but not of completely uniform pattern, having a whorled appearance and of higher echogenicity than the testicular parenchyma. There was no acoustic shadowing and no cystic architecture or fluid was identified. Colour Doppler imaging showed no detectable vascularity within the mass. The ultrasonographic appearance was similar to that described by Mak et al. (2004) who described a whorled echopattern and no vascularity in a leiomyoma of the tunica albuginea in man.


Surgical excision was elected based on the fairly rapid


growth of the masses and progression of bilateral signs. An incisional biopsy was not performed as castration enabled diagnosis and treatment in the same procedure, when financial limitations existed and there was no requirement for future fertility. Surgical excision was performed by way of closed castration with primary skin closure, under general anaesthesia, using standard surgical technique (Schumacher 2012). The testes, with their associated masses, were freely mobile within the vaginal tunics.


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