Monthly Archives: December 2019

Pericardial versus pleural effusion on PLAX view

We may find both pericardial and pleural effusions in the parasternal long axis (PLAX) view and mistaking one for the other can lead to inappropriate management. The descending thoracic aorta is the anatomical landmark to differentiate between these two effusions. Fluid anterior to the descending aorta (toward the top of the screen) is pericardial effusion and the fluid at or posterior is likely pleural effusion. Here is a cross section of thorax demonstrating the relationship of the descending aorta to the left lung and pleura.

Here are two sonographic images illustrating this concept.

Below is an example of left pleural effusion in a patient with malignancy that can be easily confused with pericardial effusion on quick beside exams. Pay attention to the location of descending aorta. Scanning in different views helps further. Also note fibrin stranding in the 2nd image suggestive of exudative pleural effusion.

Maternal Physiologic hydronephrosis in Pregnancy

Pregnancy-related hydronephrosis, more precisely physiologic maternal renal pelvis dilatation is common and the incidence is estimated to be as high as 80%. The dilatation of the pelvis and ureter typically develops toward the end of second trimester and disappears within a few weeks after delivery. It is more common in primigravid women and usually more prominent on the right side. Etiology includes extrinsic ureteral compression by the gravid uterus on top of reduced ureteral smooth muscle tone and peristalsis due to progesterone effect.

Right sided predominance may be due to dextrorotation of the uterus by the sigmoid colon, kinking of the ureter as it crosses the right iliac artery, and/or proximity to the right ovarian vein. Following figure gives an idea of the anatomy.

In these cases, it is often difficult to trace the ureter to the point of obstruction. However, in pathologic hydronephrosis, one may visualize the source of obstruction (e.g. stone). In addition, if the pelvic diameter exceeds 10 mm, pathologic dilatation should be suspected.

Here is a case of mild bilateral hydronephrosis in a primigravid pregnant woman during third trimester. Note weak left ureteral jet compared to normal. Color Doppler could not pick up the right jet despite maintaining the probe position for approximately 2 minutes consistent with obstruction.

The Shred Sign

As we have seen previously, lobar consolidations tend to be well-defined, often accompanied by a small pleural effusion. However, small subpleural consolidations (of course, ultrasound does not detect if they are not subpleural) are separated from the surrounding aerated lung by an irregular margin, like a torn paper called the ‘shred sign’. The brightness is because of the air, which scatters the ultrasound beam. It is also known as the fractal line. Here is an illustrative image.

Another example

Sometimes, the consolidation might appear anechoic mimicking a pleural effusion. But the presence of shred sign as in this example is specific to consolidation.