Guidance from The American College of Chest Physicians

The American College of Chest Physicians (ACCP) advocate measuring the apex-to-copula distance and judges any distance greater than 3 cm to represent a large pneumothorax. The use of a fixed landmark, the cupola (apex of the dome of the thoracic cavity) offered a more reproducible measurement for clinicians in comparison to the rather vague ‘lung edge to chest wall’ 2003 recommendation of the BTS. However, the 2023 BTS guidelines clarified the measurement at the level of both hilum and apex, usually ≥ 2cm laterally or apically on CXR.