Fleischner Society Thoracic Imaging Glossary 2024: Practical Terminology

The 2024 Fleischner Society glossary standardizes the words used to describe thoracic anatomy, physiology, and imaging abnormalities. Its practical value is consistency: a descriptive term should communicate an observable imaging feature without silently implying an unproven diagnosis. Terms must still be interpreted in the clinical setting and in relation to acquisition technique.

Anatomic foundations

• The acinus is the gas-exchanging unit distal to a terminal bronchiole and is not normally resolved on CT.
• The secondary pulmonary lobule is the smallest unit outlined by connective-tissue septa; its center contains a bronchiole and pulmonary artery branch.
• Interlobular septa, fissures, pleural surfaces, and bronchovascular bundles provide the landmarks used to classify disease distribution.
• Small-airway disease is often inferred from indirect findings such as tree-in-bud nodules, mosaic attenuation, and expiratory air trapping.

Attenuation and air-space terms

• Ground-glass opacity is increased lung attenuation through which vessels and bronchial walls remain visible.