A lump on the top of the right testicle may be caused by epididymal cyst, spermatic cord syringomyelia, testicular tumor and other diseases. 1. Epididymal cyst: Epididymal cyst is a common cystic disease in the scrotum of men. The cause of the disease is not yet clear, and it may be related to obstruction of the vas deferens, chronic infection and trauma. Most patients have no symptoms, and a few will have mild pain and scrotal swelling. If the cyst is large in size, it can lead to a mass on the top of the right testicle. 2. Seminal cord syringomyelia: Seminal cord syringomyelia can be manifested as a unilateral lump in the groin or above the testis, which is caused by the closure of two segments of the syringomyelia in the process of development and the non-closure of the inter-segmental part of the syringomyelia. If you have spermatic cord syringomyelia, there will be a lump on the top of the right testicle. 3. Testicular tumor: Testicular tumor can also be manifested as a scrotal or spermatic cord mass on one side, which is a solid mass with hard texture. The cause of the tumor is not yet clear, and it is related to cryptorchidism, orchitis, genetic abnormality, etc. The causative factors include drugs, environment and life style. There are more reasons for the lump on the top of the right testicle, and patients are advised to seek medical examination for a clear diagnosis.