Right upper lobe collapse
When analyzing images in the frontal projection (frontal radiograph), right upper lobe atelectasis often appears as an apical cap of fluid (apical cap of fluid). If the collapse is dense (massive), which is typical for lumen obstruction by a central bronchogenic carcinoma, a marked increase in density (opacity) in the right paramediastinal region is visualized.
In the lateral projection (lateral radiograph), a key marker of the pathology is the cranial displacement (upward) of the oblique fissure (oblique fissure).
Computed tomography (CT) provides a more accurate spatial picture. The collapsed upper lobe forms a soft-tissue attenuation area with a rough wedge-shaped or triangular form. This non-aerated zone is located in the anterior parts of the right hemithorax and directly abuts the right mediastinal border.
Middle lobe syndrome
This syndrome represents atelectasis of the middle lobe of the right lung occurring with bronchiectasis.
- Etiology: The condition arises due to focal bronchostenosis, which is secondary to pulmonary tuberculosis (pulmonary tuberculosis).
- Imaging features: On tomographic slices, the collapsed tissue appears as a relatively flat layer.
It is important to understand that theoretically such a pathological process can affect any lobe of the lung, but it is the middle lobe that is most frequently affected.
Lower lobe atelectasis
The radiographic picture of right and left lower lobe collapse is very similar. Pathomorphologically, the process is accompanied by the posterior and medial displacement of the oblique fissure (oblique fissure). The collapsed lobe is localized in the posteromedial part of the thorax (this topography is most clearly visible on CT).
Frontal projection findings:
- The collapsed lower lobes form a triangular density (triangular density) hidden behind the cardiac silhouette.
- The silhouette sign occurs: the medial part of the hemidiaphragm (hemidiaphragm) may be obscured because it is no longer outlined by the adjacent aerated lung tissue.
- Anatomical nuance: If the inferior pulmonary ligament (inferior pulmonary ligament) is incomplete and does not attach to the diaphragm, the medial contour of the diaphragm may remain visible.
Lateral projection findings:
- The posterior part of the corresponding diaphragmatic dome is often not visualized.
- In pronounced (severe) atelectasis, the diaphragmatic contour may reappear. This is due to the diaphragm beginning to be outlined by the aerated tissue of the compensatorily hyperexpanded (hyperexpanded) upper lobe.
Spine sign
Special attention in lower lobe collapse on lateral radiographs should be paid to the spine sign.
Normally, vertebrae become more radiolucent in the inferior direction (appear dark on the image). In lower lobe atelectasis, the opposite picture is observed: the shadow of the spinal column becomes progressively denser (lighter) in the inferior direction due to the superposition of non-aerated lung tissue.
Briefly: answers to topical questions
What does atelectasis of the right middle lobe look like on a lateral chest radiograph?
On the lateral radiograph, atelectasis of the middle lobe of the right lung is visualized as a wedge-shaped opacity with its apex directed toward the lung root. The collapsed lobe appears on cross-sections as a relatively flat layer of tissue. The collapsed middle lobe is clearly visualized in the lateral projection.
Which segments of the right lung are involved in the process during middle lobe atelectasis?
In middle lobe atelectasis of the right lung, the lateral and medial bronchopulmonary segments of the middle lobe are involved.
What are the direct and indirect radiological signs of lung atelectasis?
The cardinal radiological signs of lobar collapse are increased density and volume loss. Direct signs include displacement of interlobar fissures, crowding of pulmonary vessels and bronchi, and changes in the lung root. Indirect signs encompass compensatory displacement of neighboring structures, including hyperinflation of other lobes.
What is the radiological picture of left upper lobe atelectasis?
The radiological picture of left upper lobe atelectasis in the frontal projection is characterized by a veil-like increase in density of the entire left hemithorax. The left heart border, left mediastinal contour, and aortic arch become obscured. On the lateral projection, the anterior contour of the ascending thoracic aorta is unusually clearly visible.
Spine sign: "Lights up downwards — look for pathology." Normally on a lateral view, vertebrae darken downwards, while in lower lobe atelectasis, the shadow paradoxically becomes denser (lighter).
Class and exam questions
What does massive upper lobe atelectasis look like on a frontal radiograph?
It manifests as an increase in density (opacity) in the right paramediastinal region. The cause may be bronchial obstruction by a central bronchogenic carcinoma.
Why does the diaphragmatic contour disappear in lower lobe atelectasis?
The silhouette sign occurs: the diaphragmatic dome is no longer outlined because there is no longer aerated lung tissue next to it to create a natural contrast.
What is middle lobe syndrome?
This is atelectasis of the middle lobe of the right lung with the presence of bronchiectasis, arising due to focal bronchostenosis against the background of a prior tuberculosis infection.
What else to study on this topic
- Compensatory hyperexpansion of unaffected lobes
- Anatomy and role of the incomplete inferior pulmonary ligament in diaphragmatic visualization
- Differential diagnosis of collapse and apical cap of fluid
- Mechanisms of silhouette sign formation on radiographs
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