Collapse of lung lobes and thier findings in x ray and ct With images and explaination

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Lobar Collapse of the Lung - Radiological Findings on CXR and CT

Source: Grainger & Allison's Diagnostic Radiology

Introduction

Collapse (atelectasis) refers to loss of volume within the lung. The terms are often used interchangeably. "Lobar collapse" specifically means complete loss of volume within an entire lobe.

Cardinal radiographic features of any lobar collapse:

Increased opacity of the affected lobe (due to retained fluid + loss of aeration)
Volume loss - demonstrated by direct and indirect signs

Sign Type	Examples
Direct	Displaced interlobar fissures, displaced vessels/bronchi
Indirect (compensatory)	Hyperinflation of adjacent lobes, mediastinal shift, diaphragm elevation, hilar displacement, rib crowding

Absence of air bronchograms within the collapsed lobe suggests a central obstructing lesion (tumor vs. pneumonia).

Mechanisms and Causes

Category	Examples
Intrinsic endobronchial obstruction	Bronchogenic carcinoma (most common in smokers), mucus plugs, foreign body, carcinoid, metastases, granulomas (TB, sarcoid)
Extrinsic compression	Hilar/mediastinal lymphadenopathy, mediastinal masses, aortic aneurysm
Without obstruction	Passive collapse (pleural effusion, pneumothorax), post-radiation, rounded atelectasis

In a middle-aged or elderly smoker, lobar collapse should always raise suspicion of bronchogenic carcinoma until proven otherwise.

Golden's S Sign (important for any lobe)

When a central mass causes collapse, the fissure forms an S-shape - convex centrally (due to the mass) and concave peripherally (due to the collapse). Originally described in the RUL but can occur in any lobe.

1. Right Upper Lobe (RUL) Collapse

CXR Findings:

PA view: Increased density at the right apex adjacent to the mediastinum; the horizontal fissure is elevated and has a concave inferior border (Fig. 7.17 below)
In tight collapse: the lobe parallels the mediastinum, mimicking an apical pleural cap or mediastinal widening (Fig. 7.18/7.19)
There is often a small convexity at the hilum where the apex attaches
Compensatory hyperinflation of RML and RLL - right main bronchus/lower lobe artery course becomes more horizontal
Lateral view: Both horizontal and oblique fissures displaced superiorly and medially - ill-defined wedge-shaped superior density

CT Findings:

Roughly triangular density with the base anteriorly against the chest wall and apex at the hilum
A focal bulge of the lateral border indicates an underlying mass
Compensatory hyperinflation well-appreciated, including left upper lobe overexpansion crossing the midline

Typical RUL collapse - CXR (note concave inferior border of elevated horizontal fissure, arrow):

Right Upper Lobe Collapse - CXR showing concave inferior border due to elevated horizontal fissure

RUL collapse mimicking apical cap on frontal (A) and lateral (B) showing superior fissure displacement:

RUL collapse mimicking apical cap on frontal, lateral shows superior fissure displacement

CT of tight RUL collapse - triangular wedge anteriorly (arrow), with PET-CT fused image:

CT of tight RUL collapse showing triangular anterior wedge; PET-CT fused image showing central tumour uptake

CT axial showing RUL collapse (arrow) - triangular soft-tissue density adjacent to right mediastinum:

CT axial showing right upper lobe collapse as triangular wedge adjacent to right mediastinal border

2. Left Upper Lobe (LUL) Collapse

The LUL behaves differently from the RUL because the left lung rarely has a horizontal fissure.

CXR Findings:

Volume loss is predominantly anterior and medial (not superior like the right)
PA view: "Veil-like" hazy increased density over the entire left hemithorax - greatest at the hilum, fading out laterally/superiorly/inferiorly without a sharp inferior border
Loss of silhouette of left heart border, aortic arch, and left mediastinum
In less severe collapse: left heart border and aortic knuckle are obscured
In severe collapse: the aortic knuckle may paradoxically become visible again - the apical segment of the LLL hyperexpands superiorly and outlines the arch
Luftsichel sign: "air crescent" of hyperexpanded lung between the aortic arch and the medial collapse border
Left main bronchus reoriented with more horizontal course; angulation with LLL bronchus
Lateral view: Entire oblique fissure displaced anteriorly and medially, parallel to the chest wall

CT Findings:

Triangular soft-tissue density with apex at origin of upper lobe bronchus and base against the anterior chest wall adjacent to the left mediastinal border
Lingular segment seen as density closely opposed to the left heart border

Luftsichel sign - air crescent (arrow) between aortic arch and collapsed LUL on CXR; CT showing interposition of aerated lung:

Luftsichel sign on CXR and CT - air crescent between aortic arch and left upper lobe collapse

LUL collapse - PA and lateral views (veil-like opacity, anteriorly displaced oblique fissure on lateral):

Left Upper Lobe collapse - PA and lateral showing veil-like opacity and anteriorly displaced oblique fissure

LUL collapse - veil-like opacity with loss of left heart border and aortic arch silhouette:

Left Upper Lobe collapse showing veil-like opacity with loss of left heart border and aortic arch silhouette

3. Right Middle Lobe (RML) Collapse

Signs on the frontal CXR can be extremely subtle and easy to miss.

CXR Findings:

PA view:
- Loss of silhouette of the right heart border (variable degree) - the key sign
- If collapse is oriented parallel to the beam or patient is lordotic: triangular/sail-shaped density adjacent to the right heart border (Fig. 7.24, 7.26)
- If collapse lies obliquely, the only sign may be subtle loss of the right heart border silhouette
Lateral view: Wedge-shaped density extending anteriorly from the hilum toward the sternum - this is the most reliable view (Fig. 7.24)

CT Findings:

Narrow wedge of soft tissue anteriorly adjacent to the heart - best seen on coronal reformats

RML collapse - PA (loss of right heart border, arrow) and lateral (wedge-shaped anterior density from hilum, arrow):

Right Middle Lobe collapse - PA view shows loss of right heart border; lateral view shows anterior wedge-shaped density

"Middle lobe syndrome" refers to chronic RML collapse with bronchiectasis due to focal bronchostenosis (classically from tuberculosis).

4. Right and Left Lower Lobe (RLL/LLL) Collapse

The features are similar for both sides.

CXR Findings:

PA view: Triangular density behind the heart - "sail sign" or "triangular shadow behind the cardiac silhouette" (Fig. 7.27)
- Loss of clarity of the medial hemidiaphragm (no longer outlined by aerated lung)
- If inferior pulmonary ligament is incomplete, the medial diaphragm contour may still be visible
Lateral view:
- Posterior hemidiaphragm contour not visualized
- Spine sign: Vertebral column appears progressively denser inferiorly - this is the opposite of the normal pattern and is a reliable sign of lower lobe collapse

CT Findings:

The collapsed lobe lies in the posteromedial portion of the chest
Oblique fissure displaced posteriorly and medially
Compensatory hyperinflation of the upper lobes well demonstrated

Summary Table

Lobe	PA CXR Key Finding	Lateral Key Finding	CT Key Finding
RUL	Apical opacity, elevated horizontal fissure with concave inferior border	Both fissures displaced superiorly	Triangular anterior wedge, apex at hilum
LUL	Veil-like opacity entire hemithorax, loss of left heart/aortic silhouette, Luftsichel sign	Oblique fissure displaced anteriorly (parallel to chest wall)	Anterior triangular density adjacent to left mediastinum
RML	Loss of right heart border silhouette (subtle), sail-shaped density	Anterior wedge from hilum to sternum	Narrow anterior wedge adjacent to heart
RLL/LLL	Triangular density behind heart, loss of medial hemidiaphragm	Spine sign (denser inferiorly), posterior diaphragm not seen	Posteromedial opacity, posteriorly displaced oblique fissure

CT - Special Advantages Over CXR

Eliminates superimposition of overlying structures
Multiplanar reconstructions (coronal, sagittal) clarify fissure displacement
Identifies the cause of collapse (endobronchial mass, mucus plug, lymphadenopathy)
Detects distal air bronchograms (often visible in neoplastic collapse on CT, unlike CXR prediction)
Better characterization of compensatory changes

All images and content sourced from Grainger & Allison's Diagnostic Radiology, Chapter 7 (Lobar Collapse).

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