Pneumothorax

British professional guidelines have traditionally stated that the measurement should be performed at the level of the hilum (where blood vessels and airways enter the lung),^[4] while American guidelines state that the measurement should happen at the apex (tip) of the lung.^[9] The latter method may overestimate the size of a pneumothorax if it is located mainly at the apex, which is a common occurrence.^[4] The various methods correlate poorly, but are the best immediately available ways of estimating pneumothorax size.