Atelectasis

Definition

• Goldman-Cecil Medicine, p. 918

Types and Pathophysiology

1. Obstructive (Resorptive) Atelectasis

• Most common type
• Caused by bronchial block to entry of air; gas distal to the obstruction is absorbed into the bloodstream
• Intrinsic obstruction: mucous plugs, foreign bodies, endobronchial tumors
• Extrinsic obstruction: peribronchial lymph node enlargement, mediastinal masses compressing the airway
• Results in retractile consolidation

2. Passive / Relaxation / Compression Atelectasis

• Occurs when the lung recoils to a smaller volume because of fluid (pleural effusion) or air (pneumothorax) in the adjacent pleural space
• The lung collapses away from the chest wall

3. Dependent / Hypostatic Atelectasis

• Lung bases and posterior segments are vulnerable
• Caused by inadequate ventilation, especially in immobilized or postoperative patients
• Gravity-dependent alveolar closure

4. Patchy Atelectasis

• Caused by alveolar filling processes such as hemorrhage and pulmonary edema
• Surfactant dysfunction (e.g., ARDS, neonatal RDS) promotes this pattern

5. Rounded Atelectasis (Folded Lung)

• Caused by pleural thickening that invaginates and traps adjacent lung
• Characteristically occurs in dorsal peripheral lower lobes
• Strongly associated with asbestos-related pleural disease and other chronic pleural diseases
• Appears as an ovoid mass-like density abutting the pleura
• Goldman-Cecil Medicine, p. 918; Grainger & Allison's Diagnostic Radiology

Clinical Features

• Tintinalli's Emergency Medicine; Goldman-Cecil Medicine

Postoperative Atelectasis - Special Context

• Inadequate clearance of secretions after general anesthesia
• Decreased intra-alveolar pressure
• Postoperative pain causing splinting and hypoventilation
• Most frequent after upper abdominal and thoracic surgery
• Tintinalli's Emergency Medicine

Diagnosis

Chest X-Ray

• Loss of lung volume
• Displacement of lobar fissures, mediastinum, or diaphragm toward the involved lung (key sign of volume loss)
• Plate-like (discoid/Fleischner lines): horizontal or curvilinear opacities - common with subsegmental atelectasis
• Triangular densities or frank lobar consolidation

Fig. 1 - Right Upper Lobe Atelectasis (CXR)

Plain chest radiograph demonstrating right upper lobe atelectasis caused by an endobronchial tumor - Goldman-Cecil Medicine, p. 918

CT Scan

• Demonstrates the type and cause of atelectasis more precisely
• Can differentiate rounded atelectasis from parenchymal tumor
• Key CT features of rounded atelectasis:
  • Subpleural location
  • "Comet tail" sign - crowding of bronchi and vessels curving from the mass to the hilum
  • Strong, homogeneous enhancement after IV contrast (atelectasis enhances; tumor usually does not)
  • Stable on serial examinations

Fig. 2 - Rounded Atelectasis (CT)

CT image of rounded atelectasis - Goldman-Cecil Medicine, p. 918

Fig. 3 - Round Atelectasis - HRCT (axial and sagittal)

HRCT axial (A) and sagittal reformation (B) showing subpleural consolidation and the curved bronchovascular bundle ("comet tail") toward the atelectasis - Grainger & Allison's Diagnostic Radiology

Bronchoscopy

• Required to confirm intrinsic vs. extrinsic compression in obstructive-resorptive atelectasis
• Determines the exact pathology of obstruction (tumor vs. mucous plug vs. foreign body)
• Can be therapeutic (mucous plug removal)

Bedside Ultrasound

• Increasingly used to confirm the diagnosis, particularly in ICU/postoperative settings

Treatment

Prevention and Non-pharmacologic Measures

• Incentive spirometry: widely prescribed after surgery; however, no RCTs have definitively proven its effectiveness
• Preoperative inspiratory muscle training and recruitment maneuvers: may reduce atelectasis after upper abdominal and cardiac surgery
• Prophylactic non-invasive ventilation (NIV): may reduce pulmonary dysfunction after lung resection surgery
• Positive expiratory pressure (PEP) devices and high-frequency chest wall oscillation: used but of no proven benefit
• Pain control: essential to enable deep breathing postoperatively
• Patients with mild atelectasis and no hypoxemia can be managed as outpatients with pain control and encouraged deep breathing
• Admit if: hypoxemia, underlying lung disease, debilitated patient, or diagnosis uncertain
• Goldman-Cecil Medicine, p. 918; Tintinalli's Emergency Medicine

Complications

• Hypoxemia - from V/Q mismatch (most common)
• Superimposed infection / pneumonia - from retained secretions in collapsed lung (especially postoperative)
• Bronchiectasis - in CF patients, untreated atelectasis can progress to severe bronchiectasis of the affected segment/lobe

Recent Evidence