In this radiology lecture, we review the ultrasound appearance of torsion of the appendix testis and appendix epididymis! Key teaching points include: * Appendix testis is a vestigial appendage usually located between upper pole of testis and head of epididymis. * AKA hydatid of Morgagni, the appendix testis is commonly present as a normal finding. * Appendix epididymis typically arises from epididymal head. * Both scrotal appendages are often pedunculated which increases risk of torsion. * Torsion occurs when appendage twists, occluding blood supply. * Torsion of the appendix testis is one of most common causes of acute scrotal pain in prepubertal children. * Peak age 7-12 years old, but can occur at any age. * Normal appendix testis: Oval-shaped, less than 6 mm in size, homogeneously isoechoic to epididymis, and demonstrates little to no blood flow on color Doppler. * Torsed appendix testis: 6 mm or larger in size, variable echogenicity, hypoechoic before 24 hours, hyperechoic or heterogeneous after 24 hours. * In setting of appendix torsion, hyperemia of surrounding structures with hydrocele and scrotal wall thickening often present. * Torsed appendage can detach and become free floating in s*****m. * Patients may present with pain localized to upper pole of testis or epididymis. * Physical examination may yield the “blue dot” sign: Small, palpable nodule at superior aspect of testis with bluish discoloration of overlying skin due to ischemic appendix. * Cremasteric reflex typically intact, and testicle not high riding (unlike testicular torsion). * Hyperemia of surrounding structures can be difficult to differentiate from bacterial epididymitis. * However, in children, epididymitis usually secondary to inflammation from direct trauma, torsion of a scrotal appendage, or urine reflux into epididymis. Urine dipstick/urinalysis helpful to differentiate from infection. * Treatment: Pain management with analgesics, ice, rest. If not recognized, may be treated unnecessarily with antibiotics. Scrotal exploration may be necessary if testicular torsion cannot be excluded. References: Baldisserotto M, Ketzer de Souza JC, Pertence AP, Dora MD. Color Doppler sonography of normal and torsed testicular appendages in children. AJR 2005; 184:1287–1292 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! Website: https://radiologisthq.com/ Spotify Video Podcast: https://bit.ly/spotify-rhq Instagram: https://www.instagram.com/radiologistHQ/ Facebook: https://www.facebook.com/radiologistHeadQuarters/ Twitter: https://twitter.com/radiologistHQ Reddit: https://www.reddit.com/user/radiologistHQ/