Orchitis can occur when the epididymis is infected, as part of epididymo-orchitis Epididymitis and Epididymo-orchitis Epididymitis is inflammation of the epididymis (the coiled tube on top of the testis that provides the space and environment for sperm to mature), and epididymo-orchitis is inflammation of the... read more . When infection involves only the testes, it is called orchitis.
Orchitis is most often caused by a virus, usually the mumps virus. Rarely, it is caused by other infections. About 20 to 25% of men who have mumps develop orchitis. Most cases of mumps orchitis occur in boys younger than 10 years.
Orchitis may affect one testis or both testes. Long term, it may cause the testis to shrink but usually does not decrease production of the male hormone testosterone. Orchitis may diminish fertility, particularly if it affects both testes and/or occurs after puberty. However, infertility is rare.
Orchitis is usually diagnosed by physical examination. Sometimes blood tests and urinalysis are done to identify the mumps virus or other infections. Sometimes Doppler ultrasonography Doppler ultrasonography Ultrasonography uses high-frequency sound (ultrasound) waves to produce images of internal organs and other tissues. A device called a transducer converts electrical current into sound waves... read more is used urgently to assess blood flow to the testes (to rule out testicular torsion Testicular Torsion Testicular torsion is the twisting of a testis on its spermatic cord so that the blood supply to the testis is blocked. Testicular torsion causes sudden, severe pain and later swelling of the... read more , which is an emergency).