Ultrasound of the pleural cavity and lungs

Evaluation of Effusion and Loculated Collections

Ultrasound diagnostics demonstrates high efficacy in detecting loculated collections of fluid in the pleural cavity. The topographic precision of the method allows for planning drainage, which in complex cases may require the placement of multiple catheters simultaneously.

In addition, ultrasound assists in the preliminary assessment of the nature of the fluid. If septa (septations) are visualized within the effusion or increased echogenicity is determined, this highly likely indicates the presence of an exudate. However, it is important to remember that these ultrasound patterns do not always directly correlate with the presence of a purulent process and are not an absolute indication for immediate surgical intervention. The clinical picture always remains the priority.

Diagnosis of Pneumothorax

Ultrasound is considered an extremely accurate method for verifying pneumothorax, which is particularly relevant for critically ill patients examined in the supine position.

Normally, the lung moves relative to the chest wall, but in pneumothorax, the picture changes. The diagnosis is established based on the following characteristic ultrasound signs:

• Absence of the "lung sliding" sign (loss of lung sliding). Important condition: the patient must not have prior pleural fixation (e.g., as a result of pleurodesis).
• Visualization of the "lung point" (lung point) in B- and M-modes. This is a specific boundary where a mobile, partially collapsed lung is intermittently visualized against the background of the parietal pleura (stationary air).
• Enhancement of reverberation artifacts known as A-lines (A-lines).
• Complete absence or sharp decrease in the number of comet-tail artifacts — B-lines (B-lines).
• Change in the M-mode pattern: the normal "seashore sign" (seashore sign) is replaced by the "stratosphere sign" (stratosphere sign, also known as the "barcode sign").

Alveolar Recruitment and Diaphragmatic Function

Bedside ultrasound plays a crucial role in intensive care, especially in mechanically ventilated patients with severe respiratory failure.

Assessment of Alveolar Recruitment: Ultrasound can be used to estimate the proportion of alveoli actively participating in gas exchange. This is a critically significant parameter for selecting and adjusting mechanical ventilation strategy. Given that transporting unstable patients to the radiology department involves enormous risks, ultrasound serves as an attractive and completely safe (radiation-free) alternative to computed tomography.

Diaphragmatic Assessment: Real-time examination allows the physician to observe diaphragmatic excursion (movement). If the amplitude of its movement is reduced, this has direct diagnostic significance and may indicate diaphragmatic paralysis.

Endoscopic and Endobronchial Ultrasound

For deeper visualization of chest and mediastinal structures, specialized techniques are used: endoscopic (EUS) and endobronchial (EBUS) ultrasound.

Endoscopic Ultrasound (EUS): The technique utilizes a high-frequency ultrasound transducer located at the distal tip of the endoscope. This provides high-resolution images of the gastrointestinal tract wall and adjacent tissues. Linear echoendoscopes allow the needle to be seen parallel to the instrument axis, which is ideal for punctures.

• EUS-FNA (transesophageal fine-needle aspiration): minimally invasive biopsy of subaortic, subcarinal, paraesophageal, and pulmonary ligament nodes.
• Used for staging non-small cell lung cancer (confirming N2/N3 stages).
• The sensitivity of the method is 84%, and the specificity for detecting malignant lymph nodes is 99.5%.

Endobronchial Ultrasound (EBUS):

• EBUS-TBNA (transbronchial needle aspiration): performed with a convex probe mounted on a bronchoscope.
• Allows biopsy sampling from upper mediastinal, paratracheal, subcarinal, root (hilar), and interlobar lymph nodes.
• The pooled sensitivity for mediastinal lymph node staging reaches 90%.

Clinical Case Example: Contrast-enhanced CT may visualize an upper lobe lung tumor with mediastinal invasion and suspected paratracheal node involvement. In such a situation, EBUS provides clear local visualization of these nodes for targeted fine-needle aspiration.

US Guidance in Biopsies and Method Limitations

Standard transthoracic ultrasound is a fast and highly effective guidance method when performing percutaneous needle biopsy. It allows for precise needle navigation to peripheral lesions in the lungs, pleura, or chest wall tissues, minimizing the risk of complications.

Key Limitation: Despite all its advantages, ultrasound has a fundamental physical limitation—it virtually does not propagate through gas media. Therefore, the method is completely inapplicable for assessing a pathological focus if unmodified, air-filled lung tissue lies between the ultrasound probe on the skin and the target itself.

Class and exam questions

What else to study on this topic

• Lung Ultrasound Artifacts: Physics of A-line and B-line Formation.
• Features of Non-Small Cell Lung Cancer Staging (N2/N3) Using EUS-FNA.
• Protocols for Assessing Alveolar Recruitment in ICU Patients.
• Differential Diagnosis of Causes of Diaphragmatic Paralysis.
• Topographic Anatomy of Mediastinal Lymph Nodes for Endoscopic Ultrasound.

Other topics in the «Chest Radiology» section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.