The “seashore sign” is a crucial finding in lung ultrasound, appearing in M-mode as a distinct pattern. It represents normal lung sliding, with the static chest wall (skin, fat, muscle) appearing as horizontal lines in the upper part of the display, resembling the “waves” of the sea.
Below this, the moving lung pleura creates a granular, “sandy” appearance, akin to a beach. This characteristic pattern confirms the presence of visceral and parietal pleural movement, effectively ruling out pneumothorax in the scanned area and indicating healthy lung function.