000 Atelectasis

Atelectasis refers to a condition characterized by the partial or complete collapse of lung tissue, resulting in a loss of aeration in the affected areas. On imaging, atelectasis manifests as increased lung opacity with associated volume loss. It can involve a small segment of a lobe, an entire lobe, or even a whole lung, and it is often accompanied by secondary changes in adjacent structures.

Compressive Atelectasis
88 year old male with bilateral effusions shown on the CXR. Axial CT shows thickened pleura on the left with compressive atelectasis of the lower lobe and a smaller region of crescentic compressive atelectasis on the right. 3D reconstruction shows atelectasis of the left lower lobe and portion of the lingula
Ashley Davidoff MD TheCommonVein.net 74242b01d

Radiological Features

  1. Chest X-Ray (CXR):
    • Increased Opacity:
      • Dense, homogenous opacification in the collapsed region.
      • Atelectasis of the Superior Segment of the Left Lower Lobe
        72 year old female with left upper lobe mass 1 day after bronchoscopy which was complicated by lung collapse (atelectasis). The CXR has returned to baseline with segmental atelectasis caused by a left hilar mass.  Note elevation of the left hemidiaphragm  and crowding of the ribs reflecting the volume loss and confirming atelectasis
        Ashley Davidoff MD TheCommonVein.net 134476.8
    • Volume Loss Indicators:
      • Shift of the mediastinum, trachea, or heart toward the affected side.
      • Elevation of the hemidiaphragm on the affected side.
      • Rib crowding over the collapsed region.
    • Displacement of Structures:
      • Hilum moves inferiorly (lower lobe atelectasis) or superiorly (upper lobe atelectasis).
    • Air Bronchograms:
      • Visible air-filled bronchi within the collapsed lung tissue.
  2. CT (High-Resolution CT – HRCT):
    • Direct Signs:
      • Crowded, collapsed lung parenchyma with increased attenuation.
      • Wedge-shaped opacity, especially in lobar atelectasis.
    • Indirect Signs:
      • Volume loss and compensatory hyperinflation of adjacent lung segments.
      • Displacement of fissures (e.g., major or minor fissures collapsing toward the atelectatic region).
      • Pleural effusion or masses contributing to atelectasis.
    • Air Bronchograms:
      • Confirms that the airways remain open despite alveolar collapse.

Types of Atelectasis

  1. Post Obstructive  (Resorbtive)
    • Caused by
      • complete obstruction
        • neoplasm,
        • mucus plugging
        • foreign bodies
    • Result
      • air
        • no new air can enter lung distal to the obstruction
        • trapped air that is absorbed into the capillaries, l
      • pleura
        • cannot separate
        • vacuum and
        • traction of mediastinal structures and diaphragm
          • mediastinal shift and elevated diaphragm
    • CXR Right Upper Lobe Collapse Squamous Cell Carcinoma
      55-year-old male presenting with dyspnea
      Frontal CXR shows right upper lobe (RUL) atelectasis characterized by rightward deviation of the trachea elevation of the right hemidiaphragm and opacification of the right upper lobe. Final diagnosis was a central RUL proximal squamous cell carcinoma with extensive filling of the distal bronchi-ectatic segmental and subsegmental airways
      Ashley Davidoff TheCommonVein.net 212Lu 136430
      Lateral CXR Right Upper Lobe Collapse Squamous Cell Carcinoma
      55-year-old male presenting with dyspnea
      Lateral CXR confirms atelectasis of the RUL characterized by pie shaped consolidation of the anteriorly position right upper lobe, hyperinflation of the right lower lobe mild elevation of the right hemidiaphragm. Final diagnosis was a central RUL proximal squamous cell carcinoma with extensive filling of the distal bronchi-ectatic segmental and subsegmental airways
      Ashley Davidoff TheCommonVein.net 212Lu 136430
      CT – Right Upper Lobe Collapse Central Squamous Cell Carcinoma
      55-year-old male presenting with dyspnea
      Axial CT at the level of the carina shows atelectasis of the RUL caused by a central obstructing lesion in the right upper lobe bronchus resulting in atelectasis of the RUL characterized by a wedge-shaped consolidation of the anteriorly positioned right upper lobe. The major fissure is displaced anteriorly. There is extensive filling of the distal bronchiectatic segmental and subsegmental airways of the RUL. Final diagnosis was a central RUL proximal squamous cell carcinoma.
      Ashley Davidoff TheCommonVein.net 212Lu 136432c
      CT – Right Upper Lobe Collapse Central Squamous Cell Carcinoma
      55-year-old male presenting with dyspnea
      Axial CT at the level of the carina shows atelectasis of the RUL caused by a central obstructing lesion in the right upper lobe bronchus (b, white arrowhead) resulting in atelectasis of the RUL characterized by a wedge-shaped consolidation of the anteriorly positioned right upper lobe. The major fissure is displaced anteriorly (a, pink arrowhead). There is extensive filling of the distal bronchiectatic segmental and subsegmental airways of the RUL (b, yellow arrowheads). Final diagnosis was a central RUL proximal squamous cell carcinoma.
      Ashley Davidoff TheCommonVein.net 212Lu 136432cL
      CT – Right Upper Lobe Collapse Central Squamous Cell Carcinoma
      55-year-old male presenting with dyspnea
      Coronal CT at the level of the trachea and mainstem bronchi, shows atelectasis of the RUL caused by a central obstructing lesion in the right upper lobe bronchus (b, white arrowhead) resulting in atelectasis of the RUL characterized by a wedge-shaped consolidation of the right upper lobe with superiorly displaced major fissure (a, pink arrowhead). There is extensive filling of the distal bronchiectatic segmental and subsegmental airways of the RUL (b, yellow arrowheads). Final diagnosis was a central RUL proximal squamous cell carcinoma.
      Ashley Davidoff TheCommonVein.net 212Lu 136433cL

      Endoscopy Central Obstructing Mass in the Right Upper Lobe Bronchus
      Endoscopic image of a central squamous cell carcinoma (SCC) with extensive
      Ashley Davidoff TheCommonVein.net 212Lu 136434
    • Compressive Atelectasis
      • Caused by
        •  pleural effusion,
        • pneumothorax and
        • diaphragmatic abnormality
      • Result
        •  air
          • squeezed out of lung
        • pleura
          • separated
          • potentially only minor or no vacuum
            • Compressive Atelectasis Secondary Effusion
              CT with Moderate Right Pleural Effusion, Small Left Effusion  and Compressive Atelectasis
              92-year-old female presents with  dyspnea.
              CT scan shows a moderate sized right pleural effusion with compressive atelectasis (magnified in b). There is relative hyperenhancement of the compressed and atelectatic lung due to increased tissue density. At the left lung base, there is a small effusion with a minor degree of atelectasis. (magnified in c) 
              Ashley Davidoff MD TheCommonVein.net 118437c01

              Compressive Atelectasis Secondary Effusion
              CT with Moderate Right and Small Left Pleural Effusions with  Compressive Atelectasis
              92-year-old female presents with a dyspnea.
              CT scan shows a moderate sized right pleural effusion , magnified in b (yellow asterisk )  with compressive atelectasis (teal arrowheads) .  There is relative hyperenhancement of the compressed and atelectatic lung due to increased tissue density. In the  left lower lung field , there is a small effusion (yellow arrowhead ,c) with a minor degree of compressive atelectasis (teal arrowheads, c ) 
              Ashley Davidoff MD TheCommonVein.net 118437c01L

          • Compressive Atelectasis Secondary Effusion
            CT with Moderate Right Pleural Effusion and Compressive Atelectasis
            92-year-old female presents with a dyspnea.
            CT scan shows a moderate sized right pleural effusion with compressive atelectasis and on the left, there is a small effusion with a minor degree of atelectasis. There is relative hyperenhancement of the compressed and atelectatic due to increased tissue density. 
            Ashley Davidoff MD TheCommonVein.net 118437c
    •  (e.g., ARDS, neonatal respiratory distress syndrome).
    • Radiology: Diffuse or patchy opacities without significant structural shifts.
  3. Cicatricial (Fibrotic) Atelectasis: aka Cicatrisation (Traction) Atelectasis
      • Caused by
        • graulomatous disease,
        • necrotizing pneumonia and
        • radiation fibrosis
        • bronchietasis
      • Result
        •  air
          • lung cannot expand
        •  pleura
            • cannot separate
            •      vacuum and
        •       traction on surrounding structures
          Lung collapse due to scarring or fibrosis (e.g., post-tuberculosis, chronic inflammation).
    • Radiology: Dense, irregular opacities with volume loss and architectural distortion.

Gravity Dependent Atelectasis (Dependent Atelectasis)

      • Caused by​
        • weight of the lungs
      • Result
        • Crescentic shaped
      • ground glass changes

Rounded Atelectasis

    • Specific subtype associated with pleural diseases (e.g., asbestos exposure).
    • Radiology: Curved opacity with a “comet-tail” sign (curved bronchovascular structures leading to the atelectatic area).

Common Locations and Patterns

  • Lobar Atelectasis:
    • Right middle lobe: Collapses medially, causing a triangular opacity on lateral CXR.
    • Right lower lobe: Posterior triangular opacity with diaphragm elevation.
    • Left upper lobe: Band-like opacity with leftward mediastinal shift.
  • Segmental Atelectasis:
    • Localized collapse of individual segments, often subtle on imaging.

Differential Diagnosis

Radiological findings of atelectasis can mimic other conditions:

  • Pneumonia:
    • Typically shows no volume loss or mediastinal shift.
  • Pleural Effusion:
    • Causes opacity but usually shifts structures away from the effusion.
  • Mass or Tumor:
    • May cause atelectasis but with focal mass effect or irregular borders.

Clinical Context and Imaging Role

  • Atelectasis can be:
    • Acute: Post-surgical, mucus plugging.
    • Chronic: Fibrotic processes or prolonged obstruction.
  • Radiology provides critical clues to identify the cause, extent, and impact of atelectasis and helps guide further interventions like bronchoscopy or drainage.
  • Atelectasis implies collapse of part of the lung.
Collapsed lung tissue to the left with slit-like spaces representing markedly compressed alveoli.
File source: commons.wikimedia.org/

 

Types

Links and References

Links and References

TCV