A lump in the left testicle may be caused by epididymal cyst, testicular tuberculosis, testicular tumor, etc., which should be promptly consulted to find out the cause. 1. Epididymal cyst: Epididymal cyst refers to the cystic mass occurring in the epididymis, often manifested as scrotal swelling, epididymal round or ovoid swelling, etc., so there is a small lump in the left testicle which may be caused by epididymal cyst. 2. Testicular tuberculosis: Testicular tuberculosis is caused by mycobacterium tuberculosis invading the testicles, often manifested as testicular pain, swelling, enlargement, lumps, etc. So a small lump inside the left testicle may be caused by testicular tuberculosis. 3. Testicular tumor: Testicular tumor refers to the tumors occurring in male testicles, mostly malignant tumors, often manifested as enlarged testicles, painless lumps, dull pain in scrotum, lower abdominal swelling, etc. Therefore, there is a small lump in the left testicle, which may be caused by testicular tumor. This symptom alone is not enough to diagnose the disease, and may be caused by other factors. It is recommended that the patient consult a doctor in time to clarify the cause of the disease and give targeted treatment.