Unilateral testicular mastocytoma in a Peruvian Paso stallion

James A. Brown, M. A. O'Brien, A. D.J. Hodder, T. Peterson, A. Claes, I. K.M. Liu, B. A. Ball

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


A 12-year-old Peruvian Paso stallion was examined for scrotal swelling and unilateral testicular enlargement of 4-6 weeks duration. Physical examination and ultrasonography of the scrotum revealed an enlarged, nonpainful right testis with a well encapsulated mass at the cranial-medial aspect containing echodense flocculent material. Unilateral castration was performed and the testis, spermatic cord and vaginal tunic were submitted for histological examination, which revealed a mastocytoma with accompanying evidence of malignancy. Short-term follow-up examination did not reveal any evidence of abdominal metastasis and the stallion has since successfully achieved pregnancy in a small number of mares. Although considered rare, mast cell neoplasia should be considered as a differential diagnosis when unilateral testicular enlargement is encountered.

Original languageEnglish
Pages (from-to)172-175
Number of pages4
JournalEquine Veterinary Education
Issue number4
StatePublished - Apr 2008


  • Horse
  • Mastocytoma
  • Neoplasia
  • Stallion
  • Testis

ASJC Scopus subject areas

  • Equine


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