Testicular atrophy is a condition wherein the testicles gradually shrink in size. It may be caused by a number of factors

Mnemonic to master the differentials of testicular atrophy is : TESTES SHRINK:

Trauma
Exhaustional atrophy
Sequelae
Too little food
Elderly
Semen obstruction
Sex hormone therapy
Hypopituitarism
Radiation
Inflammatory orchitis
Not descended
Kleinfelter's