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Compendium August 2013 (Vol 35, No 8)

Clinical Snapshot: Dripping Fluid From the Prepuce of a Paint Horse

by Adam Stern, DVM, CMI-IV, CFC, DACVP

    Case Presentation

    A 25-year-old, castrated Paint horse presented with a 1-day history of dripping red fluid from its prepuce. On physical examination, the horse had red-tinged fluid oozing from the preputial orifice. On closer examination, an ulcerated mass, 12 cm in diameter, was identified on the tip of the penis. The distal end of the penis was surgically amputated, and the mass was submitted for histopathologic examination (FIGURE 1).

    1. What is the most likely diagnosis for this lesion?

    2. What are some treatment options for this lesion?

    3. Are there predisposing factors for development of this lesion?

    Answers and Explanations

    1. Grossly, the mass had an irregular surface and had infiltrated and partially effaced the distal end of the penis. Histologically, the mass was composed of nests and trabeculae of neoplastic epithelial cells (FIGURE 2), with evidence of dyskeratosis and keratin pearl formation. Based on the gross and histopathologic examination findings, this mass was consistent with penile squamous cell carcinoma (SCC).

    SCC is the most common neoplasm of the equine external male genitalia, and the glans penis is the most common site for development of this tumor on the equine external genitalia.1 Metastasis to the inguinal lymph node is not uncommon, with reports in five of 41 horses1 and four of eight horses.2

    2. Several options have been reported for treating penile and preputial SCC. Treatments include cryosurgery, partial phallectomy, segmental posthetomy, partial phallectomy and sheath ablation, and en bloc penile and preputial resection with penile retroversion and inguinal lymph node removal.1–3 In one report of inguinal lymph node removal in conjunction with en bloc penile and preputial resection, recurrence of SCC was observed in one of four horses with confirmed inguinal lymph node metastasis.2 Horses that have undergone only partial phallectomy have a high incidence of recurrence compared with horses that have undergone en bloc resection and preputial resection with penile retroversion and inguinal lymph node removal.2 In the case reported here, partial phallectomy was performed without removal of the inguinal lymph nodes. Partial phallectomy as therapy for SCC is associated with a high incidence of tumor recurrence compared with en bloc resection, which is associated with a low overall incidence of tumor recurrence.2

    3. Horses with SCC of the external genitalia are typically older: in one study, the mean age of affected horses was 17.4 years (range: 4 to 26 years).1,3 Geldings are more commonly affected than stallions.1,3

    1. Howarth S, Lucke VM, Pearson H. Squamous cell carcinoma of the equine external genitalia: a review and assessment of penile amputation and urethrostomy as a surgical treatment. Equine Vet J 1991;23(1):53-58.

    2. Van Den Top JGB, De Heer N, Klein WR, Ensink JM. Penile and preputial squamous cell carcinoma in the horse: a retrospective study of treatment of 77 affected horses. Equine Vet J 2008;40(6):533-537.

    3. Mair TS, Walmsley JP, Phillips TJ. Surgical treatment of 45 horses affected by squamous cell carcinoma of the penis and prepuce. Equine Vet J 2000;32(5):406-410.

    References »

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