Fibropapilloma of the glans penis in a horse.

This research article describes a case where an 18-year-old Arabian stallion presented symptoms of stranguria (difficulty urinating), which was found to be caused by fibropapilloma, a type of tumor, on the glans penis. The tumor, once removed and microscopically evaluated, was confirmed not to be a sarcoid, another common type of tumor in horses, or caused by Bovine papillomavirus or Equine herpesvirus.

Case Presentation

• The 18-year-old Arabian stallion was reported to have stranguria, which means difficulty in urinating. On physical examination, varying sizes of nodular masses, grayish-pink and glistening in appearance, were found circumferentially surrounding the external urethral orifice (the outlet of the urinary bladder) of the horse’s penis.
• Due to the observed condition, a partial penile amputation was performed on the stallion to remove these abnormal growths. The removed specimens were then submitted for histological evaluation – an examination of the microscopic anatomy of the tissues.

Diagnosis

• Microscopic examination of the masses revealed them to consist of a significant amount of fibrovascular stroma (connective tissue) with low numbers of fibrocytes (connective tissue cells). The skin covering the masses was found to have mild to moderate hyperplasia – abnormal cell growth which is usually indicative of a benign tumor or premalignant condition.
• The researchers diagnosed the lesion as fibropapilloma, a benign tumor caused by papillomaviruses, due to characteristics similar to bovine penile fibropapilloma, including the anatomical location and histological characteristics.
• Initially, the possibility of the mass being a sarcoid (a common benign tumor in horses) was considered. However, this was ruled out as the lesion did not show a classical spindle cell population, a “picket-fence” appearance at the skin interface, or long and thin rete ridges typical of most equine sarcoids.
• PCR (polymerase chain reaction), a technique used to amplify and detect specific DNA sequences, was used to test for the presence of Bovine papillomavirus-1 and Bovine papillomavirus-2 E5 genes and for Equine herpesvirus 1, 3, and 4 in the formalin-fixed tissue specimens. The results were negative, meaning these viral factors did not contribute to the development of the lesion.