Revisiting pleural effusion
Identification of pleural effusions is one of the basic applications of Internal Medicine and Nephro POCUS. As previously discussed, pleural fluid appears as an anechoic area above the diaphragm surrounding the atelectatic lung. Whale tail and spine signs are usually seen. This post is sparked by a recent twitter poll where more than 50% of the respondents could not identify right pleural effusion in relation to the inferior vena cava (IVC). We discussed the pertinent anatomic correlation in a previous post but it’s time to refresh our memory. Here is the image that I tweeted and corresponding poll results.
Below is the labeled image. Also note that there is a small pericardial effusion.
Here is the same pleural effusion seen from the traditional right lateral window. Whale tail and spine signs are clearly seen.
Below is the transverse view of the right pleural effusion from the right lateral window.
Following are two other views of the right pleural effusion from the subxiphoid window. To visualize the heart, aim the beam slightly to the left.
This patient also had left pleural effusion as shown below. Aorta is frequently visualized while imaging the left effusion, which may be confused with an abnormal structure/loculation in oblique views. It may also be confused with IVC but remember that IVC enters the right atrium just above the diaphragm and won’t be seen in the chest. Moreover, we are imaging from the left, not right.
Non-loculated effusions accumulate in the most dependent portions of the thorax that is, the posterolateral costophrenic recesses in supine patients and anteriorly in mechanically ventilated patients in prone position. Therefore, it is conceivable that ultrasound is better at detecting effusions than a portable one-view chest X-ray, which we obtain in most hospitalized patients. In a meta-analysis, pooled sensitivity of ultrasonography for detection of pleural effusion was 0.94 (95% CI: 0.88-0.97, p<0.001) compared to that of chest X-ray: 0.51 (95% CI: 0.33-0.68; p<0.001). Moreover, POCUS is good at characterizing the effusions (simple vs complex). Below is the portable AP chest X-ray from our patient done on the same day as POCUS. Provides no additional information and probably underestimates the effusions. Why subject patients to additional radiation if your focused clinical question can be answered by physical examination (i.e., POCUS), that too with a better diagnostic accuracy? On the other hand, proper training of the POCUS operator is vital because, a fool with a tool is still a fool!