• Clinical science



Atelectasis is a loss of lung volume that may be caused by a variety of ventilation disorders, for instance, bronchial injury or an obstructive mass such as a tumor. It may be categorized as obstructive, nonobstructive, postoperative, or rounded. Clinical features depend on the severity and extent of atelectasis, ranging from no symptoms to respiratory distress. Physical examination reveals a dull note on percussion and diminished breathing sounds over the affected area. On x-ray, the atelectatic section of the lung appears condensed and, due to decreased lung volume, may extend to the surrounding tissue. This effect can lead to an elevated diaphragm and mediastinal shift to the affected side. Treatment depends on the underlying cause. Complications of atelectasis include pneumonia or, depending on the extent of disease, respiratory failure.


  • Obstructive atelectasis (most common): airway obstruction (e.g., by a foreign body, mucus plug, malignancy) → nonventilated alveoli → reabsorption of gas in the poststenotic space → lung collapse
  • Nonobstructive atelectasis
    • Compression atelectasis: external space-occupying lesion (e.g., pleural effusion) that compresses the lung → forcefully pushes air out of the alveoli
    • Adhesive atelectasis: surfactant deficiency or dysfunction → increases surface tension of alveoli → instability and collapse (e.g., acute respiratory distress syndrome (ARDS) in adults, respiratory distress syndrome in premature infants)
    • Cicatrization atelectasis: parenchymal scarring that leads to contraction of the lung (e.g., chronic destructive lung processes such as tuberculosis and fibrosis)
    • Relaxation atelectasis: loss of contact between parietal and visceral tissue (e.g., pneumothorax, pleural effusion)
    • Replacement atelectasis: All the alveoli in an entire lobe are replaced by tumor (e.g., bronchioloalveolar cell carcinoma) → loss of volume → lung collapse
  • Postoperative atelectasis: one of the most common post-operative complications (especially after chest or abdominal surgery); often occurs within 72 hours of surgery
  • Rounded atelectasis: folding of the atelectatic lung tissue (with fibrous bands and adhesions) to the pleura (e.g., asbestosis)
  • Middle lobe syndrome: intraluminal or extraluminal obstruction or no identifiable cause of obstruction → recurrent or fixed atelectasis of the right middle lobe and/or lingula (e.g., associated with childhood asthma, Sjögren syndrome)


Clinical features

  • Symptoms depend on the acuity and extent of atelectasis.
    • Small number of affected alveoli or slowly manifesting atelectasis → asymptomatic or minimal symptoms
    • Large number of affected alveoli or rapid onset → acute dyspnea, chest pain, tachypnea, tachycardia, and cyanosis
  • Dull percussion note, diminished breath sounds, and decreased fremitus over the affected lung



  • Arterial blood gas analysis: hypoxemia, potentially low PaCO2, and respiratory alkalosis
  • Chest x-ray and CT: evidence of lobar collapse
    • Direct signs: displacement of fissures and homogeneous opacification of the collapsed lobe
    • Indirect signs
      • Elevation of ipsilateral diaphragm
      • Displacement of the hilum and mediastinal structures towards the affected side
      • Loss of volume in the affected side of the chest
      • Increased lucency and overinflation of the unaffected lung; silhouetting of the diaphragm or the heart border
  • Bronchoscopy (diagnostic and therapeutic): A biopsy may be performed if the etiology is uncertain despite imaging (e.g., to exclude malignancy) and mucus plugs can be removed.


Differential diagnoses

Pulmonary sequestration

  • Definition: rare congenital malformation in which a mass of nonfunctional pulmonary tissue has no connection to the bronchial tree and does not participate in gaseous exchange
  • Epidemiology
    • Intrapulmonary (surrounded by normal lobar tissue): =
    • Extrapulmonary (located outside the normal lung with its own pleura): > (4:1)
  • Clinical features
    • Usually asymptomatic
    • Symptoms may begin in the neonatal period as respiratory distress (especially with extrapulmonary type) or a chronic or recurrent cough in early childhood (usually intrapulmonary type).
  • Imaging: X-ray or CT
  • Treatment: surgical resection if there is concurrent infection or symptomatic compression of normal lung tissue


The differential diagnoses listed here are not exhaustive.


The risk of atelectasis after surgery can be avoided by prescribing opioids in doses that are sufficient for pain relief, as well as encouraging the use of incentive spirometry. At the same time, opioids should be used with caution due to their suppression on coughing. Smoking should be avoided 6–8 weeks prior to surgery.




We list the most important complications. The selection is not exhaustive.