Causes (etiology)
Loss of lung tissue air content occurs under the influence of various pathological processes. The main groups of causes:
- Inflammatory infiltration. The most frequent cause. Includes bacterial and viral pneumonias, as well as tuberculous infiltrates (including those prone to caseous necrosis).
- Patency disorders and compression (atelectasis).
- Obstructive atelectasis develops with complete occlusion of the bronchial lumen.
- Compression atelectasis occurs due to external compression of the lung (e.g., by fluid or air accumulation in the pleural cavity).
- Middle lobe syndrome (hypoventilation) is a specific condition in which the middle lobe bronchus is compressed by enlarged lymph nodes or fibrous cords. Anatomically, this area is vulnerable because even normally it is not fully ventilated.
- Vascular and hemodynamic disorders. Pulmonary infarction secondary to pulmonary embolism (PE) or local thrombosis. Congestive heart failure also leads to consolidation due to blood accumulation in the lower sections.
- Tumor growth. Replacement of air-containing tissue by neoplasms.
Clinical picture and examination data
Patients typically complain of shortness of breath. If the process is located subpleurally (close to the lung surface), the visceral and parietal pleura become involved. This manifests as pleural syndrome — chest pain appears, which noticeably intensifies on deep inspiration.
Visual inspection of the chest reveals asymmetry of respiratory movements: the affected hemithorax lags behind in the act of breathing. The shape of the chest may change depending on the cause of the syndrome:
- Bulging is observed when massive and superficially located infiltrates form (e.g., with a large tumor or pneumonia).
- Retraction (depression) is specific for extensive obstructive atelectasis, when the tissue collapses due to a lack of air.
Palpation and percussion
Dense, airless tissue conducts sound waves significantly better than healthy porous tissue. Therefore, palpation over the consolidation zone reveals increased vocal fremitus.
The main percussion sign of the syndrome is the appearance of a dull or absolutely flat (femoral) sound.
In some cases, the percussion sound acquires a mixed, dull-tympanitic shade. This occurs when the alveoli are not completely filled with exudate, contain residual air, and the draining bronchus remains patent. Such a picture is typical for:
- The initial stage (engorgement stage) and the resolution stage of pneumonia.
- The initial stage of compression atelectasis.
Auscultatory phenomena
The auscultatory picture depends on the stage of the process and bronchial patency. In lobar pneumonia at the initial stage, weakened vesicular breathing and crepitation (crepitatio indux — the sound of inflamed alveolar walls parting during inspiration) are auscultated. At the height of the disease, the alveoli are completely filled with exudate, vesicular breathing disappears, and pathological bronchial breathing is auscultated, as the consolidated tissue transmits sound from the larynx and trachea. Bronchophony is also intensified.
In compression atelectasis at the hypoventilation stage, breathing is weakened vesicular. With complete collapse, but preserved patency of the supplying bronchus, bronchial breathing occurs.
A completely different picture is seen in obstructive atelectasis (e.g., due to a tumor or foreign body). Over the occlusion zone, complete silence is auscultated — breathing is absent.
Adventitious sounds are of great diagnostic significance:
- High-pitched (consonating) fine moist rales: indicate the presence of secretion in small bronchi surrounded by a consolidation zone, which resonates the sound.
- Pleural friction rub: a marker of subpleural localization of pneumonia, tumor, or pulmonary infarction.
Briefly: answers to topical questions
What radiological signs are specific for pulmonary consolidation syndrome, apart from localized opacity?
In addition to localized opacity, sources indicate that radiography for pulmonary consolidation syndrome makes it possible to assess the shape and size of the pathological focus.
For community-acquired pneumonia as a variant of inflammatory infiltration, additional radiological signs are described:
- Localized decrease in air content — infiltration.
- Alveolar type of infiltration — consolidation: filling of alveoli with exudate, "airless" tissue.
- Air bronchogram sign — visibility of bronchial lumens against the background of consolidation.
What are the classic morphological stages of lobar pneumonia?
The classic pathomorphological course of lobar pneumonia goes through four successive stages.
- Stage of engorgement (inflammatory edema) — rapid simultaneous filling of alveoli with fibrinous exudate containing pathogens.
- Stage of red hepatization (consolidation) — erythrocytes predominate in the composition of the exudate.
- Stage of gray hepatization (consolidation) — a change in cellular composition occurs with a massive appearance of neutrophils (leukocytes).
- Stage of resolution — resorption of inflammatory changes.
The morphological substrate of these stages is the exudate, which sequentially changes its composition within the alveolar lumen.
The "open bronchus" rule: if the bronchus is patent during consolidation (pneumonia, external compression), sound is amplified (bronchial breathing, resonant rales, increased vocal fremitus). If the bronchus is occluded (obstruction) — "complete silence" ensues and vocal fremitus disappears.
Class and exam questions
Why does the character of breathing change over time in lobar pneumonia?
At the beginning of the illness, there is little exudate, and the alveoli are still expanding, so breathing is weakened and crepitation is heard. At the height of pneumonia, the alveoli are completely filled with fluid and excluded from respiration, and the consolidated tissue begins to conduct sounds from the trachea — bronchial breathing appears.
How to distinguish obstructive atelectasis from pneumonic infiltrate upon examination?
In massive pneumonia, the chest on the affected side may bulge. In obstructive atelectasis, due to complete collapse of the lung tissue, the chest on the affected side is depressed (retracted).
What do resonant fine moist rales indicate?
They indicate the accumulation of secretion in small bronchi around which a consolidation focus (infiltrate) has formed. Dense tissue conducts sound better, so the rales acquire a ringing, resonant character.
What else to study on this topic
- Mechanisms of crepitation formation in diffuse alveolitis and heart failure.
- Radiological differences between lobar and segmental consolidation.
- Differential diagnosis of types of atelectasis: obstructive versus compression.
- Anatomical prerequisites for the formation of middle lobe syndrome.
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