Fibropapilloma of the glans penis in a horse.

An 18-year-old Arabian stallion was presented for recent onset of stranguria. Physical examination of the distal portion of the glans penis revealed multiple, smooth, glistening, grayish-pink, variably sized, exophytic, nodular masses circumferentially surrounding the external urethral orifice. Partial penile amputation was performed, and the entire specimen was submitted for histological evaluation. Microscopically, the masses consisted of abundant amounts of loosely arranged fibrovascular stroma with low numbers of spindloid to stellate fibrocytes. The overlying epithelium was mildly to moderately hyperplastic with short anastomosing rete ridges (pseudoepitheliomatous hyperplasia). The lesion was diagnosed as fibropapilloma because of features similar to bovine penile fibropapilloma including anatomical location, gross appearance, and histological characteristics. A sarcoid was considered but negated as the lesion lacked the classical streaming and interlacing spindle cell population, "picket-fence" appearance at the epithelial interface, and long, thin, dissecting rete ridges typical of most equine sarcoids. Polymerase chain reaction for the Bovine papillomavirus-1 and Bovine papillomavirus-2 E5 gene and for Equine herpesvirus 1, 3, and 4 was negative on formalin-fixed tissue specimens.