“Fluid color” sign: a useful indicator for discrimination between pleural thickening and pleural effusion.

Color Doppler imaging has been applied traditionally in the evaluation of cardiovascular diseases. Recently it was observed that color signal may appear within the fluid collection in the pleural space during respiratory and cardiac cycles ("fluid color sign"). We performed this applicability of fluid color sign to the detection of pleural fluid capable of being removed to assess needle aspiration. From July 1992 to February 1994, we prospectively analyzed 76 patients who were suspected of having minimal pleural effusion on the basis of their chest radiographs. All patients were examined by color Doppler ultrasonography for the presence of fluid color sign, which was followed by needle aspiration to verify the presence of pleural effusion. Among the 65 patients with aspiratable fluid, 58 demonstrated positive fluid color sign (sensitivity 89.2%). None of the patients with solid pleural thickening showed fluid color sign (specificity 100%). With its relatively high sensitivity and specificity, the fluid color sign may be a useful diagnostic aid to real-time, gray scale ultrasonography for minimal or loculated effusion.