Epididymal Cyst: This is the most common cause of a palpable lump on the testicle, often presenting as a smooth, firm, and painless mass that can be transilluminated.

Varicocele: A varicocele is an enlargement of the veins within the scrotum, similar to varicose veins in the legs. It can feel like a "bag of worms" and is more common on the left side.
Hydrocele: This condition involves a collection of fluid around a testicle, leading to swelling of the scrotum. It can be primary (idiopathic) or secondary due to inflammation, trauma, or tumor.
Spermatocele: A spermatocele is a cystic structure that forms at the head of the epididymis and contains sperm. It is usually painless and can be transilluminated.

Testicular Tumor: Although less common, testicular cancer is a critical diagnosis not to miss. It often presents as a hard, painless lump on the testicle. Early detection is crucial for effective treatment.
Epididymitis: Inflammation of the epididymis, often due to infection, can cause a painful lump. It's essential to diagnose and treat promptly to prevent complications like abscess formation or infertility.
Testicular Torison: This is a medical emergency where the spermatic cord becomes twisted, cutting off the blood supply to the testicle. It presents with severe pain and swelling.

Adrenal Rest Tumors: These are rare, benign tumors that can occur in the testicles, especially in individuals with congenital adrenal hyperplasia.
Cystic Dysplasia of the Testis: A rare congenital anomaly where the testis is replaced by multiple cysts, presenting as a palpable mass.
Polyorchidism: A rare condition where there is more than one testis on one side, which can sometimes be mistaken for a testicular lump.