While nephrologists are not the first line of contact for trauma patients, we are often asked to evaluate the need for renal replacement therapy in these patients. It is important that we are aware of the sonographic findings seen in lung contusion so that we don’t confuse them with interstitial syndrome. As mentioned before, B-pattern in two or more sonographic lung zones bilaterally is suggestive of interstitial syndrome and this term encompasses pulmonary edema of various causes. Usually the pleural line is regular in these cases unless there is underlying lung disease such as pulmonary fibrosis.
Lung contusion is typically associated with B-lines in conjunction with pleural line irregularities, subpleural hypoechoic areas and may be localized pleural effusion. Unless the trauma is diffuse, these findings are localized to certain lung zones. The B-lines are frequently confluent, which means, too numerous and difficult to identify each line separately. In addition, Z-lines can be seen: lines that arise from the pleural line and fade away vertically and do not reach the edge of the screen.
It is also important to note that the contusion can be associated with pneumothorax, particularly in cases of rib fracture. Presence of B-lines almost always rules out pneumothorax even when you are not sure about absent pleural sliding. It is because there is air in between pleural layers, which does not allow B-lines to form. If you notice absent pleural sliding and suspect pneumothorax, look for ‘lung point’, which is the junction between normally sliding pleura and the pneumothorax with absent sliding. It is virtually diagnostic of pneumothorax.