In this radiology lecture, we review the ultrasound appearance of acute epididymitis and orchitis! Key teaching points include: * Epididymitis = Inflammation of epididymis. Usually bacterial, most commonly due to retrograde ascent from bladder or prostate. * Causative infectious agent varies based on age: Adults younger than 35: Neisseria gonorrhoeae, Chlamydia trachomatis (STDs). Adults older than 35: E. coli & other coliform bacteria. * Non-infectious causes of epididymitis: Trauma, repetitive activities such as sports (most common causes in males prior to sexual maturity), torsed appendix testis or appendix epididymis, vasculitis, and medications (amiodarone). * Presentation: Gradual onset of scrotal pain, swelling & urinary symptoms. Must exclude testicular torsion (usually more acute onset of pain). * Epididymitis US findings: Epididymal enlargement, hyperemia, hypoechogenicity. Hyperemia usually precedes grey scale changes. Infection usually spreads from tail to body and head. * 20-30% of epididymitis cases have associated orchitis: Scrotal infection typically starts with epididymis then spreads to testis, scrotal sac, or scrotal wall. * Orchitis is less common than and usually secondary to epididymitis. Isolated orchitis uncommon, usually viral (mumps). * Orchitis US findings: Testicular enlargement, hyperemia and hypoechogenicity. * Complications: Scrotal wall inflammation, complicated hydrocele, pyocele (purulent fluid collection with mass effect), abscess (epididymal, testicular, scrotal wall), testicular ischemia and infarct due to obstructed venous outflow (decreased color Doppler testicular blood flow or reversed testicular diastolic arterial flow). To learn more about the Samsung RS85 Prestige ultrasound system, please visit: https://www.bostonimaging.com/rs85-prestige-ultrasound-system-4 Click the YouTube Community tab or follow on social media for bonus teaching material posted throughout the week! Spotify: https://bit.ly/spotify-rhq Instagram: https://www.instagram.com/radquarters/ Facebook: https://www.facebook.com/radquarters/ Twitter: https://twitter.com/radquarters Reddit: https://www.reddit.com/user/radiologistHQ/