**4.4 Size of pneumothorax**

The clinical manifestations and evaluation are more important than the size of pneumothorax and do not correlate with the proportion of the pneumothorax [29]. The size of a pneumothorax is classified into three groups:


The difference of a small or large pneumothorax depends on the presence of visible rim <2 cm between the lung margin and the chest wall [29]. PA chest X-ray has been used to quantify the size of the pneumothorax. A commonly used method for estimating pneumothorax size is the light index. This method assumes that the volume of a pneumothorax approximates to the ratio of the cube of the lung diameter to the hemithorax diameter. This volume of pneumothorax can be calculated in percentage [36]. Some guidelines from the USA estimated the volume of a pneumothorax by measuring the distance from the lung apex to the cupola, and some British guidelines estimated the volume by measuring the interpleural distance at level of the hilum [29]. Pneumothorax size calculations are best achieved by CT scanning but are only recommended for difficult cases [36].
