Pitfall in lung ultrasound: 'pseudo B-line' seen in both hydropneumothorax and in a cup of coffee.

One of the lung ultrasound (LUS) signs which can be used to exclude the presence of pneumothorax is the B-line artefact. The presence of a B-line artefact indicates that the two pleural blades are in contact. Most of the research describing LUS for the diagnosis of pneumothorax is limited to pneumothorax without concomitant pleural effusion. This case report presents how a B-line was visualised using LUS in a patient with hydropneumothorax and, in addition, a simple model is used to provide a possible explanation on this phenomenon.