Main indications for ultrasound in respiratory medicine
For a long time, the application of ultrasound in pulmonology developed with some delay, but today the method has clear, universally accepted indications (besides echocardiography):
- Assessment of pleural effusion (pleural effusion). Ultrasound is the best imaging modality in this situation. It easily detects fine septa or echogenic debris that computed tomography is usually unable to distinguish.
- Examination of the thymus (thymus). Used in infants and young children.
- Suspected pulmonary sequestration (sequestration). The method allows for the identification of anomalous systemic arterial blood supply to a segment of the lung.
- Assessment of mobility. Dynamic observation of diaphragmatic dome excursion and vocal cord motion is performed.
- Costochondral junctions. Visualization of structures in the presence of local tenderness in a child (point tenderness).
Assessment of lung parenchyma: artifacts and patterns
Assessment of the lung parenchyma was long considered a controversial area due to an abundance of confusing descriptive terms (e.g., "reverberation artifact"). Today, several key patterns are distinguished:
- A-lines (A lines). Horizontal repeating lines. Considered a reliable sign of normal underlying lung parenchyma.
- B-lines (B lines). Vertical echogenic lines, also known as "comet tails" (comet tails) or "lung rockets" (lung rockets). They indicate thickening of the adjacent interlobular septa.
- Normal: may be present in a healthy lung (especially in dependent atelectasis).
- Pathology: an increase in number (more than 3 separate B-lines in a single field of view).
- Consolidation. Ultrasound is a useful adjunct in doubtful diagnoses. The method allows for the visualization of a dense lobar consolidation (e.g., middle lobe) with the presence of air bronchograms (air bronchograms) running parallel to the branches of the pulmonary artery.
Important: The use of the term "pulmonary interstitial syndrome" for an excess of B-lines is misleading. It only indicates the presence of any pathological process in the adjacent lung area, but does not provide the clinician with a specific diagnosis.
Predictive value in premature infants: Persistence of bright B-lines in the basal lung fields after the 9th day of life is a strong predictor of the later development of bronchopulmonary dysplasia (BPD / BPD).
Ultrasound-guided procedures
Due to its real-time capabilities, ultrasound has become the safety standard for invasive interventions in thoracic surgery and pulmonology. Ultrasound provides reliable visual control during:
- Diagnostic thoracentesis and therapeutic fluid aspiration.
- Insertion of chest tubes for the most complete evacuation of cavities.
- Biopsy of anterior mediastinal masses, lymph nodes, and peripheral lung lesions.
Method limitations and place in the diagnostic algorithm
The main physical barrier for ultrasound is air-filled lung tissue, which completely reflects ultrasonic waves. For this reason, the method does not visualize pathologies that do not contact the visceral pleura.
Ultrasound's "blind spots" include:
- Central structures and mediastinal lymph nodes (e.g., in tuberculosis).
- Centrally located masses and deep abscesses.
- Tubes and catheters in patients in intensive care units (ICUs).
Due to these limitations, in advanced healthcare systems ultrasound does not replace classical chest radiography (CXR). If radiography is available, it remains the first-line method.
However, in resource-limited settings (e.g., in developing countries or field conditions), ultrasound is successfully used to triage children with community-acquired pneumonia, helping clinicians determine the real need for antibiotic therapy.
Briefly: answers to topical questions
How is the air bronchogram sign visualized during lung tissue consolidation on ultrasound?
On ultrasound, the air bronchogram sign is visualized against the background of dense lung lobe consolidation.
Imaging characteristics:
- Air bronchograms (air bronchograms) — identified within an area of dense consolidation (e.g., in the middle lobe).
- Location — structures run parallel to the pulmonary arteries.
Ultrasound is a useful adjunct for assessing parenchymal status in ambiguous diagnostic cases.
How to remember the capabilities of lung ultrasound: "Ultrasound slides along the edge." The method sees only what touches the peripheral surface of the pleura (fluid, thickened septa, superficial consolidations). Everything central is hidden by air.
Class and exam questions
Can chest radiography be completely replaced by ultrasound to avoid radiation exposure in a child?
No. Ultrasound cannot see pathologies located in the center of the lung, in the mediastinum (e.g., lymph nodes in tuberculosis), or not adjacent to the pleura. Ultrasound complements but does not replace radiography.
What does the appearance of B-lines ("comet tails") on lung ultrasound indicate?
B-lines indicate thickening of the interlobular septa. Normally there may be few of them, but more than three lines in a single field of view is considered a sign of a pathological process.
What is the advantage of ultrasound over CT in assessing pleural effusion?
Ultrasound visualizes fine intrapleural septa and echogenic debris in fluid better than CT is usually able to distinguish.
How does ultrasound help predict bronchopulmonary dysplasia (BPD) in premature infants?
If bright B-lines persist in the basal lung fields of a premature infant after the 9th day of life, this is a strong predictor of the late development of BPD.
What else to study on this topic
- Radiological patterns: the "air crescent" sign and "ground-glass opacity".
- Diffuse alveolar hemorrhage (Heiner syndrome and Lane-Hamilton syndrome).
- Idiopathic pneumonia syndrome following bone marrow transplantation.
- Pediatric lung MRI: indications, functional techniques, and Fourier decomposition MRI.
- Diagnostic imaging of lymphocytic interstitial pneumonia in HIV infection.
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