Ultrasonic evaluation of pleural opacities.

Forty-one patients with substantial pleural opacities on chest films were examined by A-mode and B-mode ultrasound. Ultrasonic examination provides an accurate means of differentiating pleural fluid from other conditions which produce such opacities and is superior to the chest films as a means of localizing fluid. With the gain setting used in this series, fluid collections less than 1 cm thick were missed and were probably obscured by reverberation from the ribs. M-mode scanning provides a simple and accurate means of localizing the diaphragm in nearly all patients, almost completely eliminating difficulties caused by subdiaphragmatic placement of the thoracocentesis needle.