An encapsulated effusion is an effusion that has an envelope on the outside of the effusion that confines the effusion to a confined area. For example, an encapsulated pleural effusion, which is an encapsulation of the pleural fluid on one side of the chest wall, is usually seen on a chest radiograph as a solid, round-like shadow. On CT, normal lung tissue can be seen to be compressed, and an oval or a circular-like shadow of fluid density can be seen near the side of the chest wall. The diagnosis of encapsulated pleural effusion requires a thoracentesis with ultrasound localization. The site of thoracentesis is different from that of conventional thoracentesis. It is necessary to select the appropriate site and the appropriate angle of needle entry for thoracentesis based on the results of the color ultrasound, and sometimes it is necessary to perform thoracentesis under the guidance of the color ultrasound.