In this radiology lecture, we review the ultrasound appearance of acute appendicitis with three unique cases! Key teaching points include: * Ultrasound is the first-line imaging modality in pediatric and pregnant patients due to lack of ionizing radiation: Sensitivity/specificity approximately 80%. * Technique: Linear transducer with graded compression at site of maximal tenderness using gradual increased pressure to displace normal bowel gas. * Inflamed appendix appears as a noncompressible, blind-ending tubular structure arising from cecum. * Outer appendiceal diameter with compression: Less than 6 mm almost always normal, 6-8 mm borderline, greater than 8 mm highly suspicious. * Thickened appendiceal wall (greater than 2 mm). * Wall hyperemia: “Dot flow” normal, continuous linear/curvilinear flow highly suspicious. * Increased echogenicity and expansion of peri-appendiceal fat due to infiltration by inflammatory cells and edema. * Hyperechoic appendicolith with posterior acoustic shadowing supportive. * Identify terminal ileum separate from appendix to differentiate from ileitis, Meckel’s diverticulum, or other small bowel abnormality. * Appendix does not exhibit peristalsis. * Right lower quadrant free fluid and lymphadenopathy supportive, but nonspecific in isolation. * Loss of wall stratification suspicious for necrotic/gangrenous appendicitis, and color Doppler flow may be absent. * Gas in appendix appears as dirty shadowing and ring-down artifact. Intraluminal gas sometimes helpful to exclude appendicitis, but can also be seen with gangrenous complication. * Peri-appendiceal gas-containing collections highly suspicious for perforation. CT may be needed for clarification. References: 1) Madhuripan N, Jawahar A, Jeffrey RB, Olcott EW. The Borderline-Size Appendix: Grayscale, Color Doppler, and Spectral Doppler Findings That Improve Specificity for the Sonographic Diagnosis of Acute Appendicitis. Ultrasound Q. 2020;36(4):314-320. 2) Fallon SC, Orth RC, Guillerman RP, et al. Development and validation of an ultrasound scoring system for children with suspected acute appendicitis. Pediatr Radiol. 2015;45(13):1945-1952. 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! Instagram: https://www.instagram.com/radiologistHQ/ Facebook: https://www.facebook.com/radiologistHeadQuarters/ Twitter: https://twitter.com/radiologistHQ Reddit: https://www.reddit.com/user/radiologistHQ/