CXR findings in lung collapse

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CXR Findings in Lung Collapse (Atelectasis)

Source: Grainger & Allison's Diagnostic Radiology, Chapter 7 - Lobar Collapse

Overview

Collapse (atelectasis) refers to loss of lung volume. The two cardinal features on CXR are:

Increased opacity of the affected lobe
Volume loss - inferred by direct and indirect signs

A collapsed lobe appears dense because retained secretions/fluid replace air; however, nearly complete collapse is needed before opacity becomes obvious on CXR.

Direct Signs of Volume Loss

These are the most reliable signs:

Sign	Details
Fissure displacement	Most reliable direct sign; displaced in a characteristic direction depending on lobe affected
Crowding of vessels and bronchi	Pulmonary vessels and bronchi pack together within the collapsed lobe; often an early sign
Hilar elevation	Classic sign of upper lobe collapse; the ipsilateral hilum rides superiorly
Hilar depression / small hilum	Lower lobe collapse; the collapsed lobe obscures the lower lobe artery, making the hilum appear small rather than clearly depressed
Bronchial displacement	Upper lobe collapse swings the ipsilateral main bronchus horizontally; lower lobe collapse swings it vertically

Indirect Signs of Volume Loss

These reflect compensatory changes in adjacent structures:

Sign	Details
Compensatory hyperinflation	Remaining ipsilateral lobes expand to fill the space; hyperlucent on CXR
Mediastinal shift	Toward the side of collapse; upper lobe collapse shifts the superior mediastinum; lower lobe collapse is often less dramatic
Tracheal deviation	Toward the side of collapse in upper/whole lung collapse
Hemidiaphragm elevation	Particularly the posterior portion in lower lobe collapse
Elevation of hilum	Ipsilateral hilum pulled upward in upper lobe collapse
Herniation of contralateral lung	Especially the right lung crossing anterior midline in left lung collapse (seen on lateral view as anterior hyperlucency)

Special CXR Signs

Golden's S Sign (S Sign of Golden)

Seen in right upper lobe collapse due to central carcinoma. The collapsed lobe creates a peripheral concavity, while the central tumour mass creates a convexity - together forming a reverse-S or sigmoid curve along the displaced horizontal fissure.

Golden's S Sign - RUL collapse with central bronchogenic carcinoma showing reverse S-shaped opacity (arrows)

Air Bronchogram

Seen when airways remain patent within collapsed/consolidated lung
On CXR, suggests the collapse is NOT due to endobronchial obstruction (e.g., pneumonia causing passive collapse)
Caution: on CT, air bronchograms can still be present peripherally even with a central obstructing mass (due to collateral air drift or tumour necrosis) - so this sign is less reliable on CT than on CXR

Lobar Collapse Patterns

Right Upper Lobe (RUL) Collapse

Horizontal fissure and upper half of oblique fissure displace upward
Opacified lobe forms a wedge at the right apex, with increased paramediastinal density
On PA CXR may mimic an apical fluid cap
Lateral view: superior displacement of the oblique fissure confirms it
Tight collapse = roughly triangular anterior wedge on CT

Right Middle Lobe (RML) Collapse

Both fissures (horizontal and oblique) displace toward each other
On PA CXR, only a subtle haziness near the right heart border (loss of right heart border = silhouette sign)
Lateral view: classic triangular wedge with apex pointing toward the hilum - much better demonstrated than on PA
Middle lobe syndrome: chronic RML collapse with bronchiectasis, classically from focal bronchostenosis (e.g. post-TB)

Left Upper Lobe (LUL) Collapse

More subtle on PA CXR than RUL (no horizontal fissure on the left)
Creates a veil-like haziness over the entire left hemithorax
The aortic knuckle margin may be lost (silhouette sign)
Lateral view: oblique fissure swings forward - the collapsed lobe lies anteriorly against the chest wall

Right and Left Lower Lobe Collapse

The oblique fissure displaces posteriorly and medially
Collapsed lobe lies in the posteromedial chest
On PA CXR: triangular density behind the heart (a wedge-shaped opacity overlying the spine and heart)
Medial hemidiaphragm contour may be obscured (no longer outlined by aerated lung)
On lateral CXR: posterior hemidiaphragm may be obscured; importantly, vertebrae appear progressively denser inferiorly - the reverse of normal (normally vertebrae get darker inferiorly as overlying lung increases)
Elevated hemidiaphragm on the affected side

Total Lung Collapse

Entire hemithorax opacified
Massive mediastinal shift toward the side of collapse
Compensating contralateral lung may herniate across midline

Total left lung collapse (frontal A and lateral B). Note right lung crossing midline anteriorly (arrowheads on A) and marked anterior hyperlucency on lateral (B)

Silhouette Sign

When a collapsed/opacified lobe abuts a mediastinal or diaphragmatic border, that border is obliterated (silhouetted out):

RML collapse → loss of right heart border
LUL collapse → loss of left heart border / aortic knuckle
Lower lobe collapse → loss of diaphragm outline (medial portion)

This sign helps localize which lobe is affected.

Summary Table: Lobar Collapse on PA CXR

Lobe	Opacity location	Fissure movement	Silhouette sign	Key clue
RUL	Right apex/paratracheal	Horizontal fissure up	Right paratracheal	Golden S if tumour
RML	Right heart border region	Horizontal down, oblique up	Right heart border lost	Best seen on lateral
RLL	Behind heart, right base	Oblique fissure posteromedial	Right hemidiaphragm	Triangular retrocardiac density
LUL	Entire left hemithorax (veil)	Oblique swings anterior	Left heart border / aorta	Veil sign
LLL	Behind heart, left base	Oblique fissure posteromedial	Left hemidiaphragm	Triangular retrocardiac density

Grainger & Allison's Diagnostic Radiology, Chapter 7 (Lobar Collapse), Susan J. Copley

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