Monthly Archives: December 2019

Comet tail artefacts from metallic objects

Here are the chest ultrasound images from a cardiac surgery patient. They were obtained from the sternal area and represent comet tail artefacts from sternal wires. They look like B-lines but they are in the black background of sternal shadow rather than hazy background of the lung. Moreover, they are arranged in zig zag pattern unlike B-lines.

Note the chest X-ray from the same patient showing sternal wires.

In terms of mechanism, these are a form of reverberation artefacts where the echoes generated from the main beam are repeatedly reflected, in repeated trips before going back to the transducer. Remember, time = distance in ultrasound language and the machine places echoes making repeated trips one below the other (taking more time to reach the probe = placed below), finally creating a vertical line. On the other hand, lung B-lines are ring-down artefacts. Consider watching this video (20 min-27:30) if you need to review these and other important artefacts.

Retroperitoneal lymphoma

Here is a renal sonogram obtained from an elderly woman demonstrating bilateral hydronephrosis as well as a heterogeneous mass encasing the left kidney.

CT scan of the abdomen included for comparison: shows multilobulated retroperitoneal soft tissue mass (arrow) encasing the left kidney (LK) causing its displacement anteriorly and superiorly. Similar mass involving the right kidney (RK) can be noted, but to a lesser extent (arrow).

Unfortunately, biopsy of the mass revealed aggressive B cell lymphoma.

Learning point: Lymphoma can present as obstructive nephropathy; pay attention to the area surrounding the kidney. In fact, the diagnosis was missed on a prior point of care ultrasound in this patient.

Visualization of the right pleural effusion from the abdomen

Sometimes, pleural effusion may be noticed incidentally on abdominal scans. Below image shows transverse section of the liver with anechoic area in the posterior aspect, which corresponds to right lung/pleural area; black = fluid = pleural effusion. The bright line encircling the liver separating it from the fluid represents diaphragm.

Note the anatomic correlates – the ultrasound beam is actually oblique in between the two transverse sections shown. In such cases, go up and scan in the coronal plane to confirm your findings.

Below is a nice example showing the right pleural effusion in both transverse and coronal planes. Also note small amount of ascites in between the diaphragm and liver tissue.

Early intrauterine pregnancy

While scanning urinary bladder in women, we may occasionally encounter sonographic findings suggestive of pregnancy.  The earliest definitive evidence of pregnancy visible on ultrasonography (typically endovaginal) is the gestational sac appearing as a round, anechoic structure surrounded by thickened decidua without visible contents. At this stage, it might be difficult to distinguish true gestational sac from a pseudosac.

However, by the time it is detectable on transabdominal scans (6-7 weeks’ gestation; better seen when the urinary bladder is full), usually there are visible contents (yolk sac, fetal pole) inside the gestational sac. Visualization of a yolk sac is the first definitive evidence of an ‘intrauterine’ pregnancy. Ectopic pregnancies are rarely visible on transabdominal ultrasound but do watch for free fluid in the Morison’s pouch = could be sign of a ruptured ectopic that will likely require surgical intervention. Following are normal transabdominal images of an early intrauterine pregnancy.

Rarely, you may also find intact intrauterine contraceptive device (IUD) alongside the gestational sac (= contraception failure), which warrants immediate referral to the appropriate specialist. Following 2 cases illustrate this phenomenon.

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 mid-axillary view 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.