Pleural ultrasonography in two-dimensional mode . The pleural line is seen between two ribs. Lung sliding is abolished when both the parietal and visceral pleura do not slide while the patient is breathing. The A-line sign corresponds to the presence of linear horizontal artefacts at regular intervals below the pleural line (A-lines) without B-lines. The A-line sign is part of the ultrasound semiology of the normal lung and pneumothorax. Reproduced with permission (ACCP - Chest).