Atelectasis is the term used to describe deflated lung. There are multiple different causes of atelectasis but in the absence of endobronchial obstruction, surfactant deficiency, pneumothorax, or an adjacent space-occupying lesion compressing the lung, the most likely cause is scarring. Atelectasis due to scarring is called cicatricial or cicatrisation atelectasis and is often due to prior infection, especially mycobacterial.