Testicular diseases can be classified as endocrine disorders or as a disorders of the reproductive system. The testicles are well-known to be very sensitive to impact and injury. Blue balls is a slang term for a temporary fluid congestion in the testicles and prostate region caused by prolonged sexual arousal. The most prominent diseases of testicles are: 1  testicular cancer and other neoplasms. 2  swelling of a testicle, caused by hydrocele testis.  inflammation of the testicles, called orchitis.