Perineal swellings in two strains of mice

Seven adult male mice of two different strains and from two different animal housing facilities were submitted for necropsy to evaluate unilateral or bilateral swellings in the ventral perineal area. On dissection, the swellings were oval to spherical cystic structures located near the base of the penis. Striated muscle and a delicate stroma encapsulated all cystic structures. Cysts were firm, tan, and filled with clear, yellow fluid, or were softer and filled with white, amorphous, marbled material and a smaller amount of clear, yellow fluid. Evaluation of the cysts led us to a diagnosis of cystic bulbourethral (or Cowper s) glands. Possible causes and the incidence of this condition in other species are discussed.