If the edges of the mass and the knuckle are both visible, then the mass lies anteriorly. The loss of clarity of a structure, such as the hemidiaphragm or heart border, suggests there is adjacent soft tissue shadowing, such as consolidated lung, even when the abnormality itself is not clearly visualised. This is particularly valuable in some cases of lobar collapse. The causes of collapse Collapse usually occurs due to proximal occlusion of a bronchus, causing a loss of aeration. The remaining air is gradually absorbed, and the lung loses volume.
Patients are middle aged or elderly, and almost always smokers.
In a young adult or older child asthma is by far the commonest cause. Collapse occurs secondary to mucous plugging of the major airways, and responds to physiotherapy. In an infant consider an inhaled foreign body, such as a peanut. Retention of secretions is a frequent cause of post operative collapse. In ventilated patients, including neonates, collapse may occur if the endotracheal tube is inserted too far, entering one main bronchus and occluding the other.