Left testicular dysplasia is usually caused by trauma, torsion, surgical injury and varicocele, cryptorchidism and so on. 1. Trauma: If the left testicle is traumatized, it can cause intratesticular hemorrhage and hematoma, at first the left side looks enlarged, if not treated in time, it will affect the blood supply to the testicle, and the testicle can not be nourished by sufficient blood and cause atrophy, and in the long run, the left testicle will be much smaller than the right testicle. 2. Torsion: Testicular torsion has a rapid onset, and the patient will have severe pain in one side of the scrotum or testicle. Torsion of the testicle in the scrotum is much higher than the normal testicle and swollen, so the size of the testicle is not the same. 3. Surgical injury: after the left cryptorchid surgery, the left testicle may not be able to keep up with the normal testicle in terms of development, so there will be a big and a small phenomenon. 4. Varicocele: If the varicocele on the left side of the patient is more serious, it will easily cause the left testicle to become smaller in size. 5. Cryptorchidism: Most of the patients with cryptorchidism usually have no conscious symptoms, which may also be manifested as poor development of the left testicle, and the testicle cannot be touched in the empty scrotum. If patients have the above symptoms, they should go to the hospital in time and under the guidance of doctors to avoid delaying the condition and causing adverse consequences.