In this presentation on "HRCT: Mosaic Attenuation," Dr. Brett Elicker from the University of California San Francisco discusses the terminology and diagnostic considerations related to mosaic attenuation in chest CT scans. Dr. Elicker discusses features favoring mosaic attenuation, such as geographic nature, vessel size differences, and associated findings like air trapping. The presentation includes examples of mosaic attenuation cases and highlights the role of expiratory CT in detecting abnormalities. Constrictive bronchitis is identified as a common cause of isolated mosaic attenuation, with a differential diagnosis also includes asthma and hypersensitivity pneumonitis. Vascular causes, such as chronic thromboembolic disease, are discussed as well. Overall, Dr. Elicker provides insights into the complexities of interpreting mosaic attenuation in HRCT scans and their associated differential diagnoses.