Hi, sometimes size of two testicles are not equal. It is normal. Two testicles are present in sac called scrotum. The scrotum acts as a "climate control system" for the testes. For normal sperm development, the testes must be at a temperature slightly cooler than body temperature. Special muscles in the wall of the scrotum allow it to contract and relax, moving the testicles closer to the body for warmth or farther away from the body to cool the temperature. If any physical injury occurs to testes causes fibrosis of testes and causes shrinkage. It may be another reason for shrinkage. Consult general surgeon for furthur evaluation and treatment.