There is focal atrophy of the testicular tubules seen here. The most common infectious cause for this finding is mumps orchitis. Mumps infection may be complicated by orchitis in a fourth to a third of cases. In general, the orchitis is unilateral and patchy so that sterility following infection is uncommon. Other infectious agents associated with orchitis may include echovirus, lymphocytic choriomeningitis virus, influenza virus, Coxsackie virus, and arboviruses. In contrast, epididymitis is a more frequent cause for scrotal pain and swelling in adult males and is most likely to be the result of a sexually transmissible disease such as Chlamydia trachomatis or Neisseria gonorrheae in younger males or gram negative bacteria from urinary tract infection of older males. Disseminated tuberculosis may occasionally involve the epididymis.