B lines do not always indicate pulmonary edema
Diffuse B-line pattern can be seen in pulmonary edema of various causes, interstitial pneumonia and diffuse parenchymal lung disease (e.g. fibrosis), contusion etc. Whether you are dealing with pulmonary edema or fibrosis largely depends on the clinical context. However, findings such as irregular, fragmented pleural line, sub pleural abnormalities appearing as small hypoechoic areas and non-homogeneous distribution of B-lines favor fibrosis. On the other hand, “focal” B-line pattern may be seen in pneumonia, atelectasis, pulmonary contusion, pulmonary embolism, pleural disease and malignancy.
The following loops were obtained from upper anterior zones on each side (R/L). While they show B-line pattern, the lower lung zones were normal and the patient was breathing comfortably on room air. This is a patient with interstitial lung disease and the B-line pattern represents fibrotic process. Also note that the pleural line is irregular.
Here is another example: Images obtained from a patient with underlying malignancy and diffuse pulmonary nodules. Note the confluent B-lines, irregular pleural line and subpleural consolidation (linear probe used to take a closer look at the pleura).