From the Guidelines
Pneumothorax should be measured at the apex of the lung on an upright chest radiograph, with the measurement taken as the distance from the lung edge to the chest wall at the apex, as this is the most accurate location for determining pneumothorax size. This approach is supported by the American College of Chest Physicians Delphi consensus statement 1, which defines pneumothorax size as the distance from the lung apex to the ipsilateral thoracic cupola at the parietal surface as determined by an upright standard radiograph.
Key Considerations for Measurement
- For patients who cannot be positioned upright, a supine or semi-recumbent film can be used, though the air typically collects anteriorly and basally in these positions, making measurement more challenging 1.
- Digital measurement tools on modern imaging systems provide the most precise measurements.
- The size of the pneumothorax helps determine appropriate management strategies, with larger pneumothoraces (generally >2-3 cm at the apex) often requiring intervention such as needle aspiration or chest tube placement, while small pneumothoraces may be managed conservatively with observation 1.
Importance of Accurate Measurement
Accurate measurement of pneumothorax size is essential because it guides clinical decision-making regarding the need for intervention versus observation. The BTS guidelines for the management of spontaneous pneumothorax also emphasize the importance of accurate sizing, noting that the plain PA radiograph is a poor method of quantifying the size of a pneumothorax and that CT scanning is the most robust approach for exact size estimates 1.
Additional Imaging Modalities
While upright chest radiographs are the primary method for measuring pneumothorax size, other imaging modalities such as lateral decubitus radiographs or CT scans may be useful in certain situations, such as when the diagnosis is uncertain or in patients with complex bullous lung disease 1. However, these modalities should be used judiciously based on clinical judgment and the specific needs of the patient.
From the Research
Measurement of Pneumothorax
To determine where pneumothorax should be measured, we can look at various studies that have investigated the diagnosis of pneumothorax using different imaging methods.
- Pneumothorax can be measured using chest radiography, with posteroanterior chest radiography (PACR) being a common method 2.
- Chest ultrasound (US) is also a promising technique for the detection of pneumothorax in trauma patients, and it can be performed by emergency physicians at the bedside 2.
- The sensitivity and specificity of chest US for the detection of pneumothorax have been found to be high, with values of 88% and 99.5%, respectively 2.
- Chest X-rays (CXRs) can also be used to diagnose pneumothorax, and the use of a recommended method for interpreting CXRs can improve diagnostic accuracy 3.
- The diagnostic accuracy of CXRs can be affected by the method used to interpret them, with the recommended method showing a significant increase in diagnostic accuracy compared to the conventional method 3.
- Ultrasound detection of pneumothorax has been compared with chest X-ray and computed tomography (CT) scan, and it has been found to have a higher sensitivity than chest X-ray 4.
- The size of pneumothorax can be estimated using different methods, including the Rhea inter-pleural distances method and the CT-derived Collins method 5.
- The choice of radiographic technique for the initial diagnosis of pneumothorax is important, and posteroanterior chest radiography taken during expiration or deep breath can be used 6.
Imaging Methods
The following imaging methods can be used to measure pneumothorax: