Atelectasis (from Greek "atelec" meaning "incomplete", and "ectasis" meaning "extension") is collapse/closure of the lung, causing reduced/absent gas exchange.

• It may affect part or all of 1 lung
• Condition where the alveoli are deflated, as distinct from pulmonary consolidation

• Normal exhalation
• Pneumothorax, although atelectasis is frequently described as a collapse of lung tissue
• Post-op complication
• Due to surfactant deficiency, which in premature neonates, causes IRDS (infant resipratory distress syndrome)

• V common finding in CXR, and other radiological studies