Acute scrotal pain can be caused by several conditions. A gradual increasing intensity in scrotal pain and swelling suggests epididymitis or orchitis. Both these disorders can have infectious or noninfectious causes. In patients <35 yr, the most commonly associated organism is a sexually transmitted pathogen, such as Chlamydia trachomatis and Neisseria gonorrhoeae. In patients >35 yr, gram-negative fecal bacteria are more commonly isolated. Viral and fungal causes are rare and are typically seen only in immunocompromised patients. Noninfectious causes are thought to be related to chemical irritation from retrograde flow of urine either due to trauma or to Valsalva maneuver when lifting a heavy object. The diagnosis is primarily clinical, but in equivocal cases, scrotal ultrasonography with Doppler-flow assessment should be done.
See Epididymitis and Orchitis in The Manuals for more details.
References:
https://www.auanet.org/education/acute-scrotum.cfm
Crawford P, Crop JA: Evaluation of scrotal masses. Am Fam Physician 89 (9):723-727, 2014. doi: d10863 [pii].
Kuhn AL, Scortegagna E, Nowitzki KM, Kim YH: Ultrasonography of the scrotum in adults. Ultrasonography 35 (3):180-197, 2016. doi: 10.14366/usg.15075.
Ta A, D'Arcy FT, Hoag N, et al: Testicular torsion and the acute scrotum: Current emergency management. Eur J Emerg Med 233:160-165, 2016. doi: 10.1097/MEJ.0000000000000303 [doi].