Ultrasound is quite sensitive in detecting even very small pleural effusions; it has been demonstrated to perform better than chest x-ray and nearly as well as CT scan. In order to assess for pleural fluid, the transducer should be directed through the liver (Right side) or spleen (Left side) and diaphragm. In a normal thorax, a mirror image artifact will generally be seen above the diaphragm. When effusion is present, fluid eradicates this artifact, creating an anechoic appearance in the costophrenic angle.
The image above demonstrates a common pitfall inÂ abdominalÂ and thoracic ultrasound. The liver is visible in the near field, and a dark anechoic structure is evident just deep to the liver. Some see this fluid and may note a positive FAST examination or free intraperitoneal fluid.Â Others mayÂ see this appearance and diagnoseÂ pleural effusion or hemothorax. While it is true the anechoic area represents fluid, there is a more correct response.
The inferior vena cava can generally be seen posterior to the liver, towards the patient midline. As it is filled with blood it will appear anechoic. below the diaphragm it will course parallel and to the [patient’s] right of the Aorta. Just above the diaphragm itÂ willÂ quickly merge into the Right Atrium.
As with most scanning, fanning through multiple planes will generally sort out the true anatomy. In the clip below we see the IVC as the operator sweeps medially, and the the pleural effusion is more evident in the lateral portions of the sweep.Â One (of many) giveaways is that the hepatic veins drain into the IVC, and even in this brief sweep through the IVC a hepatic vein is visible anteriorly, draining into the IVC.