Critical Point #2: The Incomplete Scan

Once again, we are going to look at some ultrasound images critically for technique. Hitting upon the QA questions I gave you in last month's post, we'll begin with: Are these images adequate? The most common reason to have inadequate scans is that images are left out of a protocol or set that gets grouped together to make a diagnosis.

This week we are going to discuss the Renal protocol. As you may recall, a Renal protocol should include the following images at minimum:
1. Right kidney longitudinal
2. Right kidney transverse
3. Left kidney longitudinal
4. Left kidney transverse
5. Bladder (long or transverse)

In recent months I have noticed a trend that people believe that the RUQ or LUQ view may count as the longitudinal kidney view. At times, it may, but most of the times it does not. Case in point, what is wrong with the image below?


Well, although it does give us a nice view of Morrison's pouch and the diaphragm, which are essential to the FAST exam, it does not give us a complete view of the kidney. The good news is that it does include the renal collecting system as evidenced by the hyperechoic center portion of the kidney, but it does not allow us to interrogate the inferior pole of the kidney. What if the patient has a large cyst or tumor on the inferior pole of the kidney which may account for their pain? You must interrogate the entire organ in order to make a clinical decision and diagnosis.

So, you ask "How can I get around that pesky rib that is shadowing out the inferior pole of the kidney?" Here are a couple of suggestions:
1. Slide your probe down 1 rib space. This will take the focus off the kidney-liver/ spleen-kidney junction and focus on the kidney. Many times this will allow complete visualization of the kidney.
2. Sliding the probe more anteriorly, keeping the kidney in focus will often time allow you a complete picture of the kidney.
3. If that rib shadow is getting in the way no matter what, you may need to take several pictures to fully interrogate the kidney. So if you cannot get away from the rib shadow, work around it. I will often take a picture of the rib shadow bisecting the kidney, indicating to the reviewer that the rib space is tight:

This allows me to take a longitudinal measurement since both superior and inferior poles are visible.
Now I look at each pole separately. I slide my probe above the pesky rib and angle up downward to the patient's feet. This allows complete visualization of the superior and mid kidney, while blocking out the inferior pole with rib shadow.


I then slide down over that rib toward the patient's feet and angle up toward the patient's head. This image now focuses on the mid and inferior pole of the kidney.


I realize that this seems time consuming but it can be done pretty quickly as this clip illustrates:

Right Kidney Longitudinal View from UF-Jax Emergency Medicine on Vimeo.

Once the longitudinal view has been obtained, turn your probe counterclockwise 90 degree's to the patient's right to obtain the transverse view of the kidney. This seems to be easier to document since it is much easier to get between ribs in the transverse plane. Although you only need to submit 1 picture, please remember to fan through the entire organ in the transverse plane and take a representative picture. Therefore, if you have a cyst or a stone visible, take a picture of that area and denote which portion of the kidney you have in the image (superior, inferior, mid).
For the last portion of the renal exam, head to the pelvic region to scan the bladder. Remember to angle your probe to the patient's feet in order to locate the bladder. I usually begin a transverse view and then turn into a longitudinal plane. A representative picture of the bladder in either plane is acceptable.


That now completes your basic Renal Scan Protocol!

Critical Point #1

In an effort to make you all better sonologists, I will start posting some QA teaching points. I call them "critical points" because I want you to look at the images with a critical eye. These are not meant to be derogatory, but I hope, that by illustrating an error and highlighting some excellent work, I will make you a better sonologist. The whole goal of bedside ultrasound is to expedite your diagnosis. We save our images so that our consultants can view them and come to the same conclusion that we did. So try to think of your images from your consultant's perspective. Show them what you see when you make your diagnosis!

Let's start with a video, below is a clip of a subxiphoid view of the heart. There are several things to note in this clip from a quality assurance perspective:

1. Are these images adequate? To determine this, answer the questions below:
a. Is the correct probe used?
b. Is the correct exam type used?
c. Is the depth set properly
d. Is the image centered on screen?
e. Is the complete organ visible?
f. Is the gain set correctly?
g. Is the image labeled correctly?
2. Can the correct diagnosis be made from this clip?
3. If so, what is the correct diagnosis?
4. What could the sonologist do to improve the visualization of the heart?

QA #1 from UF-Jax Emergency Medicine on Vimeo.

So let's look at this video clip critically and answer each of these QA points.

1. The sonologist used the correct probe for a cardiac scan (phased arrray) and had the correct exam type selected (cardiac). Although the heart is centered on the screen, the depth is set at only 16 cm (depending on the patient's girth, 21-26cm is usual). You will note that the posterior portion of the heart appears to be cut off. This is a really big problem if you are evaluating the heart for an effusion. You expect that the fluid will collect first in the most dependant portion of the pericardium- posteriorly in a supine patient. If you cut off the posterior wall of the heart, you may be unable to determine if there is an effusion present or not. Therefore, in this video clip, the complete organ is not visible. The gain is set perfectly and allows for the fluid filled portions of the heart to appear anechoic or black, while the myocardium stands out starkly more white or hyperechoic. By not over-gaining this image, we can determine that there are no visible clots in the heart which would appear as echogenic foci (grey areas). The clip is adequately labeled so that others not present at the time of the exam can know what the sonologist intended to image.

2. The diagnosis can be made by this clip, but it is a little subtle. Note that the left ventricle is located at the bottom right in the clip. As the ventricle contracts, a thin sliver of fluid in the pericardium can be visualized. Do not be fooled by only looking anteriorly, as the pericardial fat pad can mimic an effusion. The fat pad will appear as an anechoic stripe in the near screen on the parasternal long axis view (PSLX), anterior to the right ventricle. Without an anechoic stripe in the posterior pericardium, the diagnosis of an effusion cannot be made.

3. Correct diagnosis: Pericardial effusion. It is difficult to determine if tamponade is present from this view, but the right ventricle appears to move symmetrically. Pericardial tamponade can be diagnosed on ultrasound by the presence of right ventricular (RV) collapse. This can easily be seen using the PSLX view. The RV is located in the near field and the wall will collapse inward with each contraction. It will look like someone has placed their finger on the RV and pushed in toward to the septum at that one point. Always look for tamponade on any patient with an effusion. Usually it is the small, new effusions that will cause tamponade since the pericardium has not been stretched out to accommodate the fluid collection.

4. The sonologist did a fair job in this clip, but would really make the clip better by increasing the depth of field to allow the heart and pericardium to be completely visualized. Otherwise, good job!