Collapse of lung lobes and thier findings in x ray and ct

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Lung lobe collapse (atelectasis) involves characteristic X-ray and CT findings that differ by lobe. The key signs include displacement of fissures, increased opacity, mediastinal/diaphragmatic shift, and compensatory hyperinflation of adjacent lobes.

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Collapse of Lung Lobes: X-Ray and CT Findings

Source: Grainger & Allison's Diagnostic Radiology; Goldman-Cecil Medicine

General Principles of Lobar Collapse

Direct signs of volume loss:

Displacement of fissures (the most reliable early sign)
Crowding of pulmonary vessels and bronchi within the collapsed lobe
Hilar elevation (upper lobe collapse) or hilar "smallness" (lower lobe collapse)
Bronchial reorientation: the ipsilateral main bronchus becomes more horizontal in upper lobe collapse; more vertical in lower lobe collapse

Indirect signs:

Compensatory hyperinflation of adjacent lobes (fewer, more widely spaced vessels)
Mediastinal shift toward the collapsed lobe
Diaphragmatic elevation (especially with lower lobe collapse)
Displacement of the anterior junctional line contralaterally

A collapsed lobe appears dense due to retained secretions/fluid plus loss of aeration. Near-complete collapse is needed before the lobe becomes radiographically opaque.

Schematic Overview

This diagram shows the position of each collapsed lobe on frontal and lateral projections:

Schematic Appearances of Lobar Collapses on Frontal and Lateral Radiographs (RUL, RML, RLL, LUL, LLL)

1. Right Upper Lobe (RUL) Collapse

X-Ray (PA):

Upward displacement of the horizontal (minor) fissure
Increased density in the right upper zone
Right hilum elevation
Tracheal deviation to the right
Loss of right mediastinal border silhouette
In "tight" collapse: a triangular wedge of soft tissue abuts the right mediastinum with a concave inferior margin (due to lower lobe hyperinflation) - the "Golden S-sign" when an underlying central mass causes the concavity

X-Ray (Lateral):

Upward displacement of the horizontal fissure
Anterior displacement of the upper part of the oblique fissure

CT:

Triangular wedge of soft tissue anteriorly in the right hemithorax adjacent to the right mediastinum
The collapsed lobe wraps around the superior mediastinum

Tight RUL Collapse - increased right paramediastinal density (arrow) due to central bronchogenic carcinoma

Fig. 7.19 - Tight Right Upper Lobe Collapse. The collapsed lobe (central bronchogenic carcinoma) results in increased right paramediastinal density (arrow).

2. Right Middle Lobe (RML) Collapse

X-Ray (PA):

Ill-defined density at the right heart border (loss of right heart border silhouette - positive silhouette sign)
Often subtle and easily missed
Small triangular opacity in the right lower zone adjacent to the right heart border

X-Ray (Lateral):

Wedge-shaped opacity between the horizontal and oblique fissures that converge anteriorly - the classic "bowtie" or "triangular" opacity with an anterior apex

CT:

Band-like or wedge of soft tissue at the right cardiophrenic angle
Fissures bow toward each other medially/anteriorly

3. Right Lower Lobe (RLL) Collapse

X-Ray (PA):

Triangular density in the right lower zone medially, behind the heart
Loss of silhouette of the medial right hemidiaphragm
Right hilum "appears small" (interlobar artery obscured by opaque lobe)
Right hemidiaphragm may be elevated

X-Ray (Lateral):

Triangular density posteriorly
Loss of the posterior right hemidiaphragm silhouette
Vertebral column appears progressively denser inferiorly (important sign - normally the reverse is true)
Posterior displacement of the oblique fissure

CT:

Collapsed lobe lies in the posteromedial right hemithorax
CT mucous bronchogram sign: tubular, low-attenuation branching airways within the enhancing collapsed lobe (on contrast-enhanced CT)

4. Left Upper Lobe (LUL) Collapse

This is distinctly different from RUL collapse because the left lung has no horizontal fissure.

X-Ray (PA):

"Veil-like" increased density over the entire left hemithorax, greatest at the hilum (not a sharp margin)
Loss of left heart border silhouette (lingula collapses anteriorly)
Variable loss of the aortic knuckle silhouette
Tracheal deviation to the left
Left hilum elevation with increased angulation of the left main bronchus
Luftsichel sign: a crescent of lucency (aerated superior segment of the left lower lobe) alongside the aortic knuckle, separating the aortic arch from the collapsed upper lobe

X-Ray (Lateral):

Anterior displacement of the oblique fissure (toward the sternum)
Increased retrosternal lucency (lower lobe hyperinflates anteriorly)

CT:

Collapsed lobe forms a flat, broad band of soft tissue anteriorly against the chest wall and mediastinum
Oblique fissure sweeps anteriorly

LUL Collapse - frontal radiograph shows veil opacity with increased angulation of left main bronchus (arrow). Lateral shows anterior displacement of oblique fissure.

Fig. 7.21 - Left Upper Lobe Collapse. (A) Frontal view: increased angulation of left main bronchus (arrow). (B) Lateral view: anterior displacement of the oblique fissure (arrow) with increased retrosternal lucency.

Atypical LUL Collapse - frontal CXR and CT showing triangular soft-tissue opacity

Fig. 7.22 - Atypical LUL Collapse on CXR and CT.

5. Left Lower Lobe (LLL) Collapse

Very similar in appearance to RLL collapse.

X-Ray (PA):

Triangular density medially in the left lower zone (behind the heart)
Loss of silhouette of the medial left hemidiaphragm
Left hemidiaphragm may be elevated
Loss of the descending aorta outline in severe collapse

X-Ray (Lateral):

Triangular density posteriorly
Loss of the posterior left hemidiaphragm silhouette
Vertebral column appears progressively denser inferiorly

CT:

Collapsed lobe in the posteromedial left hemithorax
Oblique fissure displaced posteriorly and medially

6. Whole Lung Collapse

X-Ray:

Complete opacification ("white-out") of the hemithorax
Marked volume loss - ipsilateral mediastinal shift (this helps distinguish it from large pleural effusion, which shifts the mediastinum away)
Contralateral lung expands across the midline anteriorly
On lateral: marked anterior hyperlucency (contralateral lung displacement greatest anteriorly)

CT-Specific Signs Across All Lobes

Sign	Significance
CT mucous bronchogram	Tubular low-attenuation airways in collapsed lobe - often indicates obstructive cause
Strong homogeneous enhancement	Favors atelectasis over consolidation/pneumonia (pneumonia shows less enhancement with air bronchograms)
Air bronchogram on CT	Does NOT exclude obstructive collapse (unlike plain film rules)
Fissure displacement	Best appreciated on coronal/sagittal reformats
Mediastinal anatomy	CT clarifies lymphadenopathy and causative masses

CT Enhancement: Atelectasis vs Pneumonia - bilateral lower lobe atelectasis shows dense homogeneous enhancement (A); bilateral lower lobe pneumonia shows relative lack of enhancement with air bronchograms (B)

Fig. 7.12 - Enhancement pattern on contrast CT: Atelectasis (A) = dense homogeneous enhancement; Pneumonia (B) = relative lack of enhancement with air bronchograms.

Quick Summary Table

Lobe	Fissure Movement	Opacity Location (PA)	Key Signs
RUL	Horizontal fissure - upward; upper oblique - anterior	Right upper zone / paramediastinal	Golden S-sign, hilar elevation, tracheal shift right
RML	Horizontal fissure - down; oblique - anterior/up	Right heart border (lateral wedge)	Right heart border silhouette loss, lateral wedge sign
RLL	Oblique fissure - posterior/medial	Behind heart, medial right lower zone	Medial diaphragm loss, vertebrae denser inferiorly
LUL	Oblique fissure - anterior	Veil over left hemithorax	Luftsichel sign, anterior fissure shift, retrosternal lucency
LLL	Oblique fissure - posterior/medial	Behind heart, medial left lower zone	Medial diaphragm loss, vertebrae denser inferiorly
Whole lung	All fissures invisible	Total hemithorax white-out	Ipsilateral mediastinal shift, anterior hyperlucency on lateral

Grainger & Allison's Diagnostic Radiology, pp. 181-194; Goldman-Cecil Medicine, pp. 918-919

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