Epididymal Cysts: These are benign, fluid-filled cysts that can form on the epididymis, which is a tube at the back of the testicle that stores and carries sperm. They are common, often painless, and can feel like small, pea-sized lumps, making them a likely explanation for the symptoms described.

Spermatoceles: Similar to epididymal cysts, spermatoceles are benign cysts that contain sperm and are located at the head of the epididymis. They are usually painless and can present as small lumps.
Varicoceles: These are enlargements of the veins within the scrotum, similar to varicose veins. While they can cause a sensation of heaviness or aching, they can sometimes be painless and might be felt as lumps, especially if they are small.
Testicular Cysts: Simple cysts of the testis are benign fluid-filled structures within the testicle itself. They are less common than epididymal cysts but can present similarly.

Testicular Cancer: Although testicular cancer is relatively rare, it is crucial to consider it in the differential diagnosis of any testicular lump. It can present as a painless lump or swelling and is more common in younger men.
Epididymitis: Inflammation of the epididymis, often due to infection, can cause swelling and lumps, although it is typically painful. However, early stages or certain types of epididymitis might not be painful, making it a "do not miss" diagnosis.
Orchitis: Inflammation of one or both testicles, usually caused by bacterial or viral infections. Like epididymitis, it can cause swelling and might be considered even if the patient reports no pain, given the potential for serious complications.

Adrenal Rest Tumors: These are rare, benign tumors that can occur in the testicles in individuals with congenital adrenal hyperplasia. They can cause testicular enlargement or lumps.
Dermoid Cysts: These are rare, benign cysts that can contain various types of tissue, including hair, skin, and sometimes even teeth. They can occur in the testicles and present as lumps.
Mesothelioma of the Tunica Vaginalis: A rare form of cancer that affects the lining of the testicle (tunica vaginalis). It can present with hydrocele (fluid around a testicle) or as a lump.