Basic radiographic signs
Diagnosis of left upper lobe atelectasis is based on a combination of conventional radiography and computed tomography findings. On a frontal chest radiograph, the pathology manifests as a characteristic veil-like opacity. This opacity merges with the left cardiac contour, completely masking its border. At the same time, an overall reduction in the volume of the left hemithorax is invariably recorded.
Contrast-enhanced computed tomography provides significantly more information and allows for precise determination of anatomical changes:
- On coronal and sagittal reconstructions, a dense wedge-shaped density is visualized, which closely abuts the mediastinal organs.
- The oblique interlobar fissure (oblique fissure) changes its normal position: on coronal slices it is pulled superiorly, and on sagittal slices it is displaced anteriorly.
- An abrupt cut-off of the left upper lobe bronchus is identified at the lung root. Most commonly, this pattern is caused by a central obstructing tumor blocking the airway lumen.
Golden's S sign on CT
The classical Golden's S sign (Golden’s S sign) occurs when a central mass prevents the collapsed lung lobe from fully retracting toward the root, forming a characteristic convex border centrally.
In conventional radiology, this sign is historically associated with right upper lobe atelectasis and is rarely reliably identified in the lower lobes. However, with computed tomography, the situation changes dramatically: the tomographic equivalent of Golden's S sign is informative and applicable to any lung lobe, including the left upper lobe. The presence of a local contour bulge of the collapsed lobe is a reliable predictor of a central neoplasm.
CT mucous bronchogram sign
Another crucial diagnostic marker is the CT mucous bronchogram sign (CT mucous bronchogram sign). Its identification indicates with a high probability that lobar collapse (lobar collapse) is caused by an obstructing mass.
The essence of the pathomorphological process is that secretions continuing to be produced in the excluded lung segment become inspissated secretions. Due to impaired drainage function, segmental and lobar bronchi dilate and fill with this thick mucus.
This phenomenon is visualized most clearly on CT after the administration of a radiocontrast agent. Against the background of actively enhancing dense tissue of the collapsed lobe (e.g., in concomitant right lower lobe atelectasis secondary to squamous cell carcinoma), branching low-attenuation branching structures are clearly visible. These are the bronchi "clogged" with mucous masses.
Etiology of obstructive lesions
The causes leading to airway obstruction with the development of atelectasis and mucus accumulation can be divided into three main groups:
- Malignant neoplasms. Primarily bronchogenic carcinoma, including squamous cell carcinoma, which frequently has a central location.
- Benign strictures. A striking example is tuberculous bronchostenosis, leading to cicatricial deformation of the bronchial lumen.
- Pathologies with hypersecretion and impaired clearance. Conditions characterized by excessive mucus production and failure of the mucociliary apparatus to clear it:
- Allergic bronchopulmonary aspergillosis (allergic bronchopulmonary aspergillosis);
- Asthma (asthma);
- Cystic fibrosis (cystic fibrosis).
Briefly: answers to topical questions
Which bronchopulmonary segments comprise the left upper lobe?
The left upper lobe includes the lingular segments, although the complete list of segments is not provided in the text.
- Lingular segments (lingular segments) — their sparing (preservation of aeration) accounts for the specific appearance of atypical left upper lobe collapse, whereas isolated atelectasis leads to loss of definition of the left heart border.
What anatomical structures form the root of the left lung?
The root of the left lung is formed by the main bronchus, blood and lymphatic vessels, and nerves.
- Main bronchus (bronchus principalis) — located inferior and posterior to the pulmonary artery.
- Pulmonary artery (a. pulmonalis) — occupies the most superior position, arching over the left main bronchus.
- Pulmonary veins (vv. pulmonales) — superior and inferior, adjacent to the anterior and inferior surfaces of the bronchus and artery.
- Lymphatic vessels — enter the general composition of the lung root.
- Nerves — represented by branches of the pulmonary plexus.
What neoplasms, besides squamous cell carcinoma, can cause central bronchial obstruction?
Central bronchial obstruction can be caused by:
- Bronchogenic carcinoma (bronchogenic carcinoma); any histological type of lung cancer can cause obstruction.
- Endobronchial metastases (endobronchial metastases), including those from melanoma, renal cell carcinoma, colorectal cancer, and breast cancer; airway obstruction is the leading sign.
How to differentiate atelectasis of the upper lobe from lobar pneumonia on a radiograph?
The following signs on a radiograph are helpful:
| Sign | Atelectasis (collapse) | Pneumonia (consolidation) |
|---|---|---|
| Air bronchogram | Presence of air bronchograms in the collapsed and consolidated lobe helps exclude a central obstructing mass | Frequently observed in lobar pneumonia |
| Luftsichel sign | Paramediastinal lucency characteristic of left upper lobe atelectasis | May be uninformative in acute bronchopneumonia |
| Nature of opacity | Veil-like opacity with volume loss of the left hemithorax | Uniform homogeneous opacity of a part or the entire lobe |
How do the positions of the mediastinal organs and the dome of the diaphragm change during volume loss of the left hemithorax?
With volume loss of the left hemithorax, the mediastinum shifts to the left, i.e., towards the affected side. In total collapse, the right lung may shift across the midline, forming a mediastinal hernia.
Elevation of the left dome of the diaphragm has been described in isolated atelectasis of the lingular segments, but has not been established in the sources as a general sign of any volume loss of the left hemithorax.
Golden's S sign: on radiographs it "favors" the right upper lobe, whereas on CT it is universal and works for all lobes.
Class and exam questions
How to distinguish an air bronchogram from a mucous bronchogram on CT?
The air bronchogram appears as branching dark (air-filled) lines against the background of consolidated lung. The mucous bronchogram (CT mucous bronchogram sign) consists of low-attenuation tubular structures (yet denser than air) identified against the background of intensely enhancing pulmonary parenchyma.
What other lobes can collapse via a similar mechanism?
Any. For instance, squamous cell carcinoma frequently presents with right lower lobe atelectasis, where linear areas of mucus accumulation are also visualized exceptionally well.
What else to study on this topic
- Radiological presentation of right lower lobe atelectasis
- Golden's S-sign: physical and radiological basis
- Differential diagnosis of bronchogenic lung cancer on CT
- Complications of tuberculous bronchostenosis
- Radiological features of cystic fibrosis and allergic bronchopulmonary aspergillosis
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