Acute inflammation of the testis or epididymis may be caused by trauma, infection (fungal, bacterial, or viral), or testicular torsion. Clinical signs are pain and swelling of the testes, epididymides, and/or scrotum. There may be wounds or other lesions in the scrotal skin. Orchitis and epididymitis are rare in cats.

The scrotal contents should be carefully palpated to identify which structures are involved, including the vas deferens and pampiniform vessels. Ultrasonography is helpful to further evaluate the affected structures and to confirm the presence of testicular torsion and focal lesions in the testis or epididymis. It will also identify less common causes of scrotal enlargement such as scrotal hernia.

Diagnostic tests should always include evaluation for Brucella canis infection. (Also see Brucellosis in Dogs.) Cytologic examination of semen with bacterial and mycoplasmal culture are also helpful, but semen collection from animals that are ill or in pain may be difficult. Testicular specimens for cytology and culture may be obtained by fine-needle aspiration. Testicular biopsy for histopathology and bacterial culture may be performed, if needed, after less invasive diagnostic tests have been completed. Because of the greater risk of granuloma formation, epididymal aspiration and biopsy are rarely done. If future reproduction is not of importance, specimens can easily be obtained at the time of castration.

Treatment is difficult unless the underlying cause can be identified. The prognosis for maintaining fertility is guarded despite aggressive therapy because of the potential for irreversible damage to the germinal epithelium, tubular degeneration, development of immune-mediated orchitis, or obstruction of the duct system. These sequelae may take months to occur. Application of cool water packs may decrease testicular damage caused by local swelling and hyperthermia. In the case of unilateral involvement, the unaffected testis/epididymis must be protected from damage by heat, pressure, and direct extension of the disease process. Hemicastration may be prudent. If bacterial cultures are positive, appropriate systemic antibiotics should be administered for 3 wk. There is no successful treatment for B canis infection. All antifungal agents interfere with spermatogenesis, either directly or indirectly.

If histopathology is suggestive of an immune-mediated process (eg, lymphocytic-plasmacytic infiltration), treatment with immunosuppressive drugs (eg, prednisone, 1 mg/kg, bid) has been suggested. However, chronic B canis infection also causes lymphocytic-plasmacytic inflammation. Furthermore, as a result of inhibitory effects on the hypothalamic-pituitary-gonadal axis, glucocorticoids can cause testicular atrophy and infertility. The ischemic damage caused by testicular torsion becomes irreversible within hours. When maintaining fertility is not important, castration is the treatment of choice for orchitis and epididymitis due to any cause. If bacterial infection is suspected, a broad-spectrum, bactericidal antibiotic should be administered for 7–10 days. Lesions of the scrotal skin are treated the same as other skin lesions.

Chronic orchiepididymitis may develop as a sequela of the acute syndrome, or there may be no previous history of testicular inflammation. Possible causes include those of acute orchiepididymitis, immune-mediated orchitis and epididymitis, neoplasia, and spermatocele or granuloma formation. Most animals are asymptomatic except for infertility. Physical examination often reveals testicular atrophy. Tumors may be palpable. Palpation of the epididymis may reveal induration or enlargement, which may erroneously be interpreted as dramatic relative to the atrophic testis. Epididymal atrophy is uncommon.

Other noninflammatory causes of testicular atrophy include previous exposure to excessive pressure, heat, cold, and cytotoxic agents. Hormonal causes (eg, glucocorticoids, estrogen from contralateral Sertoli cell tumor) are also possible.

The prognosis for return of normal fertility in cases of chronic orchitis/epididymitis is grave. If warranted by the dog's value as a stud, the diagnostic and therapeutic plan is as described above for the acute condition.

Last full review/revision July 2011 by Cheri A. Johnson, DVM, MS, DACVIM (Small Animal)