Atelectasis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sudarshana Datta, MD [2]


The pathophysiology of obstructive and non-obstructive atelectasis can be better explained by understading underlying pathology. Obstructive atelectasis, the most common type of atelectasis, occurs due to obstruction at any level from the trachea to the alveoli. Foreign bodies, tumors, and mucus plugs are the most common causes of obstructive atelectasis. Non obstructive atelectasis occurs due to severe lung scarring caused by necrotizing pneumonias or granulomatous diseases leading to cicatrisation atelectasis. Lung infiltration by a tumor (bronchoalveolar carcinoma) may cause replacement atelectasis, thoracic space occupying lesions can cause compression atelectasis, diminished levels of surfactant can lead to adhesive atelectasis presenting as ARDS. Passive atelectasis occurs due to absence of contact between the parietal and visceral pleurae due to fluid (pleural effusion), air (pneumothorax), blood (hemothorax) etc. Patients undergoing upper abdominal and thoracic procedures may develop postoperative atelectasis which may arise as a complication of surgery or anaesthesia leading to decreased surfactant activity and dysfunction of the diaphragm.



  • It is understood that atelectasis is the result of obstructive and non-obstructive etiologies.
  • The pathophysiology of obstructive and non-obstructive atelectasis is determined by several factors.

Pathogenesis of Obstructive atelectasis

  • Obstructive atelectasis is the most common type of atelectasis
  • Obstructive atelectasis occurs due to obstruction at any level from the trachea to the alveoli.
  • Ventilation defect
  • Perfusion defect
    • Perfusion of under ventilated lung tissue leads to hypoxemia due to shunt formation. leading to obstruction
    • Following bronchial obstruction, complete collapse of the affected lung is prevented by secretions that fill up the spaces of the alveoli.
    • The adjacent lung distends to prevent collapse of the part of the lung undergoing atelectasis.
    • The mediastinum shifts towards the affected side.
    • Diaphragmatic elevation of the diaphragm leads to flattening of the chest wall.
  • The extent of atelectasis depends upon the level of obstruction.
    • Lobar atelectasis occurs due to lobar bronchus obstruction.
    • Segmental atelectasis arises from segmental bronchus obstruction.
  • The rate and pattern of development of atelectasis depends on collateral ventilation and gas composition of inspired air.

Pathogenesis of Non obstructive atelectasis

Middle lobe syndrome

Associated Conditions

Common conditions associated with atelectasis include:

Gross Pathology

  • On gross pathology, pleural folds with deep invaginations are characteristic findings of atelectasis.[4]

Microscopic Pathology

  • On microscopic histopathological analysis, fibrosis and pleural invaginations are characteristic findings of atelectasis.[4]
  • If there is an existing pathology leading to atelectasis, characteristic features of the underlying disease may also be seen on microscopic pathology.


  1. "Atelectasis - Symptoms and causes - Mayo Clinic".
  2. Chen HA, Lai SL, Kwang WK, Liu JC, Chen CH, Huang DF (2006). "Middle lobe syndrome as the pulmonary manifestation of primary Sjögren's syndrome". Med. J. Aust. 184 (6): 294–5. PMID 16548837.
  3. Rosenbloom SA, Ravin CE, Putman CE, Sealy WC, Vock P, Clark TJ, Godwin JD, Chen JT, Baber C (1983). "Peripheral middle lobe syndrome". Radiology. 149 (1): 17–21. doi:10.1148/radiology.149.1.6611925. PMID 6611925.
  4. 4.0 4.1 "Pathology Outlines - Round or rounded atelectasis".

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