Epididymitis: This is an inflammation of the epididymis, a tube at the back of the testicle that stores and carries sperm. It's a common cause of scrotal pain in adolescent males, often due to bacterial infection, and its likelihood is increased by sexual activity or urinary tract anomalies.

Testicular torsion: Although less common than epididymitis, testicular torsion is a significant cause of acute scrotal pain. It occurs when the spermatic cord becomes twisted, cutting off the blood supply to the testicle. It's more common in neonates and adolescents.
Orchitis: Inflammation of one or both testicles, usually caused by bacterial or viral infections. It can occur alone or in conjunction with epididymitis (epididymo-orchitis).
Varicocele: An enlargement of the veins within the scrotum, similar to varicose veins. While often asymptomatic, it can cause a dull ache or discomfort.

Testicular torsion: Despite being mentioned under other likely diagnoses, it's crucial to emphasize its inclusion here due to its potential for severe and irreversible damage if not promptly treated. Missing this diagnosis can lead to loss of the testicle.
Appendicitis (with an appendix located near the testicle): Although rare, an appendix located near the testicle (retrocecal or pelvic appendix) can cause scrotal pain if it becomes inflamed. Appendicitis is a surgical emergency.
Henoch-Schönlein Purpura (HSP): A form of vasculitis that can cause scrotal pain and swelling, among other symptoms like rash, joint pain, and gastrointestinal issues. It's essential to recognize HSP due to its potential for complications.

Testicular cancer: While testicular cancer is rare in adolescents, it can present with a painless testicular mass. However, some patients may experience pain or discomfort.
Spermatocele or hydrocele: These are fluid-filled cysts that can cause scrotal swelling and, occasionally, discomfort or pain.
Scrotal cellulitis or abscess: Bacterial infections of the skin and soft tissues of the scrotum, which can cause pain, swelling, and redness.
Idiopathic scrotal edema: A condition characterized by sudden onset of scrotal swelling and redness, often without significant pain, and of unknown cause.