What imaging study is needed for evaluating a pneumothorax?

To evaluate a pneumothorax, an expiratory chest X-ray (CXR) is particularly useful because it can help to visualize any air that is present in the pleural space. During an expiratory view, the diaphragm is typically elevated, allowing for improved identification of small amounts of air. This technique increases the sensitivity for detecting a pneumothorax when compared to a standard inspiratory film, particularly for smaller pneumothoraces.

The choice of using an expiratory CXR is favored in clinical practice as it is readily available, quick to perform, and involves minimal risk to the patient. While CT scans offer a higher sensitivity and can provide detailed imaging of the lungs and surrounding structures, they are not always necessary for initial assessment unless there are complications or other concurrent injuries that need to be evaluated.

The other imaging modalities listed—MRI and X-ray abdomen—are not appropriate for evaluating pneumothorax. MRI is not typically used in acute settings for lung pathology due to availability, cost, and time considerations. Similarly, an X-ray of the abdomen would not provide the necessary information about the thoracic cavity and would not aid in the identification of a pneumothorax. Thus, the expiratory CXR remains the preferred initial imaging