Atelectasis is the partial or complete collapse of a portion of the lung, so that part of the lung is no longer filled with air.
Small areas of atelectasis often cause no symptoms. Larger areas may cause breathlessness, a cough, or a feeling of not getting a full breath in.
Imaging shows where the collapse is, how much of the lung is involved, and whether something inside the airway (a plug of mucus, a tumour, or an inhaled object) might be blocking it.
Chest X-ray usually picks up atelectasis first; CT shows it in more detail and can identify a blockage, mass, or surrounding consolidation.
Treatment targets the cause — breathing exercises, treating an underlying chest infection, removing an inhaled object, or addressing a tumour blocking the airway.
This entry explains the finding. The next step is having a radiologist interpret your specific scan, not a general definition.