Transthoracic lung ultrasound - the basics

Transthoracic lung ultrasound has been conducted for over 40 years. Initially, it was mainly performed to evaluate pleural fluid, but, with time, studies confirmed its usefulness in the diagnosis of lung diseases. By contrast with X-ray, ultrasound does not expose patients to harmful ionising radiation, owing to which it can be repeated many times without hazards to the patient. Transthoracic lung ultrasound enables evaluation of the pulmonary pleura, the parietal pleura, the pleural space and the pulmonary tissue itself. This review presents the scanning technique and basic artefacts observed in a normal ultrasound scan. The examination can be performed with any ultrasound machine equipped with convex and linear-array probes. The basic image is referred to as a "bat sign," i.e. the image made up by shadows of two neighbouring ribs and a hyperechoic line between them, which is the pleural line. Subsequently, the sliding sign, i.e. pleural movement, must be assessed as its absence may indicate pneumothorax. Moreover, one must search for artefacts present in normal images, such as horizontal lines parallel to the pleural line, called A-lines, and vertical lines that move according to the respiratory movements, called Z-lines, I-lines and B-lines. The knowledge of the basics of transthoracic lung ultrasound is useful in the search for pathology. Performing ultrasound examinations frequently increases one's experience, which helps to interpret this relatively simple examination.