Normal ultrasound appearance of the pleura
When examining a normal chest via ultrasound, two major visual patterns are identified. First, this is the "pleural line" (pleural stripe) — a distinct echogenic line that corresponds to healthy pleural layers. Second, vertical echogenic bands extend downward from this line. This is the so-called "comet tail" artifact (Comet Tails), which occurs due to physical reverberation artifacts of ultrasound waves. The presence of these signs rules out the presence of air between the parietal and visceral pleura.
Classification and causes of pneumothorax
Pathological accumulation of air in the pleural cavity is generally divided into several groups depending on the underlying cause:
1. Spontaneous pneumothorax
- Primary: develops in healthy individuals without visible triggers.
- Secondary: occurs against the background of other diseases. It can be triggered by airway obstructions (asthma, chronic obstructive pulmonary disease, cystic fibrosis), pulmonary infections (destructive pneumonia with cavitation, tuberculosis, fungal infections, pneumatocele, AIDS). Other causes include pulmonary infarction, neoplasms (e.g., metastatic sarcoma), and hereditary connective tissue disorders (Marfan syndrome). This group also includes catamenial pneumothorax (associated with endometriosis) and diffuse diseases (lymphangioleiomyomatosis, histiocytosis X, fibrosing alveolitis).
2. Traumatic pneumothorax
- Non-iatrogenic: the result of closed chest trauma (with or without rib fractures), penetrating wounds, or rupture of the trachea and esophagus.
- Iatrogenic: a complication of medical procedures. It occurs after thoracotomy, thoracentesis, percutaneous biopsy, tracheostomy, or central venous catheterization.
Features of primary spontaneous pneumothorax (PSP)
Excluding iatrogenic cases, this is the most common type of the disease. The pathology develops against the background of visually healthy lungs.
- Epidemiology: The disease is typical for young adults — 65% of cases occur between the ages of 20 and 40 years, with men being significantly more affected.
- Cause: In almost all cases, the trigger is the spontaneous rupture of a small apical pleural bleb (bleb).
- Diagnostics: Detecting such blebs during remission is difficult. On standard radiographs, they are visible in only 20% of patients (when protruding beyond the apical margin of the lung). Computed tomography is much more effective at finding apical air spaces.
- Prognosis: Without targeted treatment, at least 33% of patients experience a recurrence within several years, typically on the ipsilateral (same) side.
Life-threatening complications and comorbid conditions
Air accumulation may be accompanied by the development of severe conditions requiring immediate response:
- Tension pneumothorax (Tension Pneumothorax): A life-threatening complication where intrapleural pressure exceeds atmospheric pressure during a significant portion of the respiratory cycle. This critically disrupts hemodynamics and gas exchange. Important: the diagnosis is made clinically only, and treatment is initiated without performing an X-ray! If an X-ray is nonetheless performed, the most reliable sign is considered to be flattening of the diaphragmatic dome on the affected side combined with pronounced mediastinal shift. It should be noted that a slight mediastinal shift is also possible in simple pneumothorax due to the preservation of vacuum on the healthy side.
- Hemopneumothorax: Frequently accompanies trauma. In spontaneous cases, a small amount of bloody fluid is acceptable, but clinically significant hemorrhage occurs in only 2% of cases. Clotted blood on a radiograph can mistakenly mimic a pleural tumor.
- Pyopneumothorax: A rare purulent complication, usually associated with esophageal perforation or necrotizing pneumonia.
- Adhesions (Adhesions): On X-rays, they create direct linear shadows running from the lung to the chest wall. They prevent the lung from collapsing completely, but it is precisely because of them that persistent air leakage (air leakage) can continue. Rupture of adhesions is often accompanied by hemorrhage. They can be studied in detail using CT.
Briefly: answers to topical questions
What specific ultrasound symptoms confirm the presence of a pneumothorax?
The presence of a pneumothorax is confirmed by a number of specific ultrasound signs detected in various scanning modes. These include:
- Loss of lung sliding (loss of lung sliding) — provided there is no prior pleural fixation.
- "Lung point" (lung point) — intermittent visualization of the mobile, partially collapsed lung against the background of the pleura in B- and M-modes.
- Enhancement of reverberation artifacts (A-lines).
- Absence or reduction in the number of comet tail artifacts (B-lines).
- "Stratosphere sign" (stratosphere sign) — replaces the "seashore sign" (seashore sign) in M-mode.
What radiological signs are characteristic of hemopneumothorax?
A characteristic radiological sign of hemopneumothorax is the presence of clotted blood in the pleural cavity, which appears on a radiograph as a mass lesion.
- Clotted blood — forms a mass that radiologically mimics a pleural tumor.
Standard-exposure chest radiographs are used to diagnose hemopneumothorax in trauma cases.
What surgical treatment methods are used for recurrent spontaneous pneumothorax?
In recurrent spontaneous pneumothorax caused by the rupture of subpleural blebs, pleurodesis is indicated. The following surgical treatment methods are used:
- Local chemical pleurodesis — the method of choice to prevent recurrences.
- Pleurectomy — an alternative method of choice.
- Resection of subpleural blebs — used with caution, as adhesion formation can critically hinder potential future lung transplantation.
What ultrasound artifacts, besides the comet tail, are encountered during lung examination?
During lung ultrasound examination, in addition to the comet tail artifact (B-lines), reverberation artifacts are encountered.
- Reverberation artifacts (A-lines) — their enhancement is one of the ultrasound signs of pneumothorax.
The comet tail artifacts themselves (Comet Tails) are vertical echogenic bands that are also caused by reverberation artifacts.
Class and exam questions
Why is it unacceptable to wait for radiography results in tension pneumothorax?
This is a life-threatening condition where positive intrapleural pressure rapidly impairs cardiovascular function and gas exchange. The diagnosis is made clinically, and assistance is required immediately.
What is the most reliable radiological sign of tension pneumothorax?
The most reliable sign is a pronounced mediastinal shift accompanied by flattening (depression) of the diaphragmatic dome on the affected side.
What is the danger of pleural adhesions in air accumulation?
On the one hand, adhesions prevent the lung from collapsing completely. On the other hand, they can maintain a constant air leak (air leakage) from the lung surface, and their rupture can provoke hemorrhage.
Can clotted blood in the pleural cavity distort the radiographic picture?
Yes, in hemopneumothorax, clotted blood can form a mass that visually mimics a pleural tumor on an X-ray.
What else to study on this topic
- Pathogenesis of hemodynamic disorders in the development of tension pneumothorax
- Ultrasound physics: the nature of reverberation artifacts and comet tails
- The role of CT in planning surgical treatment for apical pleural blebs
- Catamenial pneumothorax: mechanisms of development in endometriosis
- Differential X-ray diagnosis of clotted hemothorax and pleural neoplasms
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