Hydrothorax, more commonly called pleural effusion, is the accumulation of fluid in the pleural space between the lungs and the chest wall. On ultrasound, pleural fluid appears as an anechoic or hypoechoic collection above the diaphragm that changes shape with respiration. Ultrasound is more sensitive than chest X-ray for detecting small effusions and can characterize whether the fluid is simple or complex, which helps determine the likely cause and need for drainage. Hepatic hydrothorax specifically refers to pleural effusion that develops in patients with liver cirrhosis when ascitic fluid passes through small defects in the diaphragm. Ultrasound is also used to guide thoracentesis, the procedure to drain pleural fluid.
Sonography Term