Ultrasound for RLQ Pain: What’s New? - HD

Introduction to Compression Sonography for Acute Appendicitis

Sheila, thanks very much and good morning to all of you.

It's always somewhat remarkable to me to reflect upon the fact that compression sonography for acute appendicitis has been on the clinical scene for over 30 years. And the fact that I'm here speaking to you this morning about six new things for you to consider in this examination, I think implies several things. First and foremost is this is not a static or even mature technology. This is an evolving and dynamic one, and yet it's one that has an extraordinary high clinical impact factor. The fact that we can diagnose with an inexpensive, readily available, non-invasive technique with no ionizing radiation and either rule in or rule out appendicitis, is incredibly powerful. And not just for the patient and the patient's family, but really for our whole healthcare delivery system. And moving forward, as we transition to a paradigm where we're going to be treating appendicitis, just like any other form of colonic diverticulitis with antibiotics, this will become even more and more important.

I have no disclaimers.

So the new things that I'm gonna talk to you about are largely in two broad areas, image acquisition and improving specificity of diagnosis.

Addressing the Limitation of Low Appendix Visualization Rates

The first thing we have to come to grips with is the major limitation of ultrasound compared to ct, and that is our low rate of visualization of the appendix. It's rare for us with a CT not to visualize the appendix, but it's all too commonplace with sonography and visualization rates, at least in North America, have traditionally been in the 25 to 30% range. And that's really too low to really have an impact because remember, we can't diagnose what we can't see.

So most studies have been done in the supine position. And when you think about it, what are our options available to us to improve our visualization? They involved a different acoustic window and a different transducer. And in fact, we've gotta employ both of these strategies.

So let's just review a few highlights of the scanning technique. It's very important to take a brief history and ask the patient if they can localize with a single finger where they hurt the most. Now, they may not be able to do that, but if they can, it's really important for us to scan in that area. And here's a young woman who points right to her umbilicus, and here we can see a hypo coic mass superficially right in the periumbilical region.

We want to take a brief history, certainly ask if this patient's had surgery. In fact, she had had surgery and this is in fact a lap port implant from endometriosis. And we see lap port implants from cancer as well. Ovarian and colon cancer are treated often laparoscopically, and it's important to look in those areas as well.

This more elderly woman pointed right to her umbilicus, and here we can see a hypo coic mass, not in the umbilical region, but in the region of the omentum. It's got flow within it. And this was this woman's presentation for her recurrence in metastatic breast cancer with a mental caking from metastatic disease. And as Mindy beautifully shown, this patient pointed right to the right kidney. There is a low bar area of increased echogenicity, a little fluid adjacent to that right kidney. And remember, the endotoxin of e coli activates complement in the microvasculature causing microvascular sludging. And so acute pilo is in fact an ischemic lesion, often seen with a little adjacent free fluid, so pyelonephritis as well.

Now, one of my favorite cases, and this gentleman came over to us for acute appendicitis and the technologist immediately got me and I went into the room and this gentleman pointed immediately to his left mid abdomen. Now you're just thinking to yourself, the ER docs at Stanford, they are amazing. They can diagnose acute appendicitis in a patient with sitis in verses. So he points to this hypo coic mast. It's quite vascular, and we can see that the mass has both an inter, it's associated with one intergenic submucosal ring and a second intergenic ring. So I was talking to the patient, have you had any surgery? And although he could not remember, his wife remembered something that I'm very familiar with actually. And he had had a scalp lesion removed, and this was his presentation for metastatic melanoma with a small bowel into subception.

So lots of different pathology you have to scan where the patient hurts. But I think that the supine position is just too limited as our only acoustic window. And I want to really emphasize the value of direct retros seql scanning for a retro SQL appendix with a steep LPO position scanning in the coronal plane along the SOAs.

So here's a CT to illustrate the nature of the problem. If we come from a supine anterior approach, we're gonna run into a lot of bowel gas in the secum and we're gonna miss this retrocecal appendix. However, if we scan the patient in an LPO coronal view and just come through the left flank, that appendix will now come into view. And I learned this the hard way. A number of years ago, we had scanned this patient in ultrasound in the morning and I was on ct that afternoon. And we had missed it because there was all this bowel gas in the cecum here. And on the CT scan there was clearly thickened enhancing appendix. No wonder we had missed it from an anterior approach.

So I just went over and got the ultrasound machine, brought it right into the CT scanner, and this was a young patient who was very accommodating. Let me do this. Here's that appendix right in that LPO position coming from the left flank approach. So we have to get behind the bowel gas in the cecum, and if we don't see the appendix in the supine view, don't stop, keep going in the LPO to look specifically for a retrocecal appendix. Again, sometimes you'll be gassed out by the right colon, but that retrocecal appendix in the coronal view will often be seen parallel to the ssas, hence the s OAS sign of acute appendicitis.

Here's another example of normal appendices seen parallel to the ssus muscle scanning along the ssus muscle in an LPO position. So if we don't see it in the supine, we have to go in the LPO and here's a normal appendix seen in the retro SQL position, only seen scanning coronal.

Now after that patient, if we still don't see it, then we flip the patient back and do a second look supine. And while there's not an enormous yield, there is an appreciable year, about eight to 10% of the appendices will only be seen in this. Remember, we've shifted the bowel gas and given ourselves and new acoustic window. And so here is the proximal base of the appendix. We'll talk a lot about this a little bit later. We'll see this thickened hypo coic lamina propria that is diagnostic of lymphoid hyperplasia, which may or may not be associated with acute appendicitis. If there is obstruction of the appendix. This is a classic mechanism for distal appendicitis if the distal tip of the appendix is fluid filled. The point I wanna make here, this appendix was only seen on that second look supine view.

So we're using three views. Now, when we look at the data from our group that we published on this, this is a training period where we got all of our technologists up to speed and then we implemented this three step positioning algorithm takes just about the same time. You can see dramatic improvement in our visualization on ultrasound. And we've maintained this high level around 50%. But look at the concomitant decrease in CT utilization. So this has a twofold benefit. One, we're making the diagnosis either normal or abnormal appendix and two, we're not running up the cost of the healthcare system and radiating young patients who don't need it.

Lessons from CT to Improve Ultrasound Visualization

Now the second thing that I want to talk to you about is why should we be happy with 50% that's still far below CT visualization? Can't we do better? What are the lessons that we've learned from CT about why we're missing all these appendices?

Well, we looked at about 200 patients in whom we still didn't see the appendix, and we looked at the ct, where is that appendix located? Maybe we're just scanning in the wrong area. And we looked to see a couple of things. First of all, we wanted to see what quadrant vis-a-vis the ileocecal valve was that appendix in. And we used the CTE to have an anterior medial and a posterior medial and lateral compartments and pay very attention to this posterior medial compartment. That's the money shot. That's where we miss things.

Next we looked at, what's this relationship to the iliac crest? Are we scanning high enough? And so we looked to see all these appies on CT that we missed with ultrasound in relation to the iliac crest. And finally we looked at the depth from the anterior abdominal wall with a mathematical fudge fracture for compression. So CT is not done with compression, but ultrasound is so sort of see get these three parameters.

And here's what we learned and published recently, 20% of the mis appies were above the iliac crest. We weren't routinely scanning there and 62% were in this medial posterior quadrant, posterior medial quadrant. That's really what we do. So after we've done everything, we've done our three step positioning, we do a dedicated attempt to look above the crest, and then we need to scan in the posterior medial quadrant.

But wait, there's more. What we also learned was that an appreciable number of the appies were too deep to see within the purview of a 10 megahertz transducer, we needed to get beyond the depth of six centimeters. So the takeaway was basically we had to change not only the patient's positioning and where we scanned, but the depth of penetration by using a lower frequency transducer. And so scanning above the egret and then targeting that posterior media quadrant and scanning with a six megahertz is really the way to go. And here's an example. We don't see it with a 10 megahertz. We do see the appendix in this. We've not been aided in this attempt by the obesity epidemic.

So this is an example of where the six megahertz depth of penetration will allow you to see that appendix. And here's a patient we're scanning above the iliac crest and was not seen below the iliac crest.

Differentiating Complicated vs. Uncomplicated Appendicitis

Alright, so one of the things that I mentioned is that antibiotic therapy will become very important as primary therapy, just like all other forms of uncomplicated diverticulitis. And what's really key is figuring out who's got gangs or perforated appendicitis because they're not appropriate for short term potentially transitioning to outpatient antibiotics, they need either inpatient, IV antibiotics or surgery. So this differentiating of complicated versus uncomplicated is very important. What I use the term complicated, what I'm really talking about is gangrene. That is a necrotic appendix or perforated.

So we had a hypothesis about that and we said, just like with the gallbladder, if we lose that because of reflectivity in areas of gallbladder necrosis, it probably is going to be similar in the appendix. And if we lose our echogenic submucosal layer, let's use that as our operative paradigm for complicated cos appendicitis.

And so this is what we did. We looked at a series of patients who had an intact submucosal layer and those that didn't absent SML, and this turns out to be an extremely powerful discriminator. Here we can see an intact submucosal layer. Here we can see complete loss of the submucosal layer in a gangrenous appendix. And here's that patient's path slide with a necrotic area. Secondary findings, often thickened echogenic fat and complete loss of the integrity of the bowel wall with inflammation out into the fat here.

So an excellent discriminator. And here's a study from our group that we published showing that this had an extremely highly associated factor if you lose your SML highly likely to be complicated appendicitis. Conversely, if that SML is intact, highly likely to be uncomplicated. So that's very useful going forward.

Improving Diagnostic Specificity with Objective Criteria

Now as we look into more objective criteria for interpreting sonography, we have to come to terms with the fact that our old criteria of maximum outer diameters are imprecise. We know that below six millimeters, it's virtually always normal. We know that eight millimeters and above, virtually always abnormal, but there's a gray zone in this intermediate area and we have to use secondary interpretive signs and those are either going to be color or fat.

So these borderline category we can't always tell. Now as it turns out, when you look at large groups of patients, and we looked at several hundred patients in this category, about two thirds will have appendicitis, but about one third won't. And sending a third of the patients to surgery is just unacceptable. So we have to have better discriminatory value in this borderline category.

So how are we gonna do that? Well, the first thing is to try to precisely define our criteria for normal or abnormal color flow in the appendix. It used to be with older generations of colored doppler, we couldn't really discriminate flow in the wall. Now we can and we can see these areas of what we call dot flow. And these are the VAs recta from the arcades in the meso appendix. And we can see these focal little areas. You can actually get spectral tracings for those, but contrast that kind of dot flow with this continuous curve linear flow. And we began sort of anecdotally to sort of see that this was far more associated with appendicitis than this.

So we wanted to test that as a hypothesis. What was the significance of dot flow versus this curva linear flow? And we define this as contiguous three millimeter or greater flow in the wall of the appendix. And some examples again, dot flow curva linear flow.

So this is what we looked at in with our hypothesis and a study from our group showed that worked pretty well in fact dot flow and we honed in on again, this borderline category. I mean, if your appendix is nine millimeters, it's acute appendicitis. Conversely, if it's five millimeters, it's normal. So where we really struggle, or again this borderline category, and this is where we wanna see a flow, can be more precise. And the data really show that this type one flow or dot flow is not associated with acute appendicitis. It's often seen with another thing. We'll talk about lymphoid hyperplasia, but I'm getting ahead of myself.

So this curve linear flow greater than three millimeters, highly predictive, highly associated with acute appendicitis.

Role of Spectral Doppler in Acute Appendicitis

Alright, well let's push that a little bit further. If we're able to visualize flow in the wall, why don't we get more in and sort of view it qualitatively. Why don't we get more quantitative data? Why don't we push this even further and get spectral doppler tracings.

So what is the role of spectral doppler in acute appendicitis? Now, when I was a surgical intern, this is what we referred to as a white owl. It's a normal appendix that's sort of a gray sort of dull surface. And this is what we call the injected appendix. And notice the difference here in the serosal vascularity, not only are there more vessels and they are more conspicuous because they're larger, but they're also tortuous. So vascular enlargement, tortuosity to us that just means, there's inherently gotta be just more flow in that. And this might be reflected in the spectral doppler tracing. So that's the hypothesis that we wanted to check.

And in fact, when we look biochemically at the pathophysiology of acute appendicitis, one of the things that we learn is that there's vaso arterial dilatation mediated by histamine. I would just say as an aside that uncomplicated appendicitis sort of ends with this kind of inflammatory cascade. But gangrenous and perforated appendicitis are almost a separate disease. Very early on in that disease they have upregulation of interleukins and cytokinin, interleukin six, interleukin 16, and the metalloproteinases that cause rapid tissue lysis. And our old paradigm, well we've gotta operate early or they're gonna perforate under our eyes is completely wrong. They have a separate metabolic cascade in terms of the inflammatory cytokine mediators and they perforate and they have this rapid tissue necrosis way before they get admitted. So it's a completely different end pathway.

But for the uncomplicated cases, we see this histamine mediated vaso arterial dilatation. And that is reflected histologically in this marked dilatation of this these ciero vessels. That's what you're seeing on the surface. That's what the quote unquote injected appendix looks like.

Now the other thing that we learned when we started to look more carefully at the histology of the appendic wall and our pathologists were really they put up with a lot with me, but Jerry Berry in particular I want to give a shout out to. 'cause he carefully looked at the walls of a lot of these patients. And what he found was that the veins were virtually always compressed by intramural infl inflammation. So concomitantly, there was both vaso arterial dilatation reflecting increased flow and venous outflow obstruction. So what does that mean from compression of the mural inflammation.

So what does that mean in terms of a hypothesis of what would we expect to see in the flow? Well, we would expect to see a higher peak systolic velocity yet with higher resistance flow. And so that may be a bit counterintuitive because we think of inflammation often as having maybe high diastolic flow. But if you go back to that histologic side slide, that venous outflow compression really results in high ris.

So this is our hypothesis that we would have increased peak systolic velocity, but with high ris. And that is in fact exactly what we saw. And so when we look at these waveforms, we can measure them from the wall and we can get a nice stop of waveform. I'll just say parenthetically, the angle correction doesn't buy you any greater specificity. We angle corrected a whole bunch of these and non angle corrected. So when you angle correct of anything, the velocities are a bit higher. So it's not absolutely mandatory to angle correct, but if you can, we try to do it here, we can see the velocities here.

So here's a quiz for you. Which one of these patients with a borderline MOD maximum outer diameter in fact has acute appendicitis? And here's a patient with a low peak systolic velocity, and here's a patient with high peak systolic velocity and high resistance. Well, as you might suspect, this is the patient with acute appendicitis with high peak systolic velocity and high resistance. And that's exactly what we see in this spectral doppler waveform.

Again, a borderline appendix between six to eight, we have to bring in secondary criteria. There's no real obvious increased fat, but the flow is abnormal. Both we see the curve, the curve sign, it's greater than three millimeters, and we see this pattern of high peak systolic velocity, high resistance, and here just other examples, et cetera, et cetera. And again, with the histology, the venous outflow obstruction.

So we put this hypothesis to test and we, by adjusting a lot of ROC curves came up with discriminatory values. And pretty much 10 to 12 centimeters is a pretty good cutoff for peak systolic velocity. If you're above that, very likely you have appendicitis with a specificity almost 90%. And that seemed to perform just slightly better than the ri. This the RI was not quite as discriminatory. So this is impress in radiology from our group. So again, we can use the spectral doppler tracing to either further our diagnostic specificity.

Pitfall: Lymphoid Hyperplasia

Now, one pitfall that has been problematic and we've made mistakes with this in the past is this entity of lymphoid hyperplasia. So let's drill down a little bit about that.

Now, the normal appendix has an abundance of t lymphocytes in the lamina propria. It's very interesting in terms of the immune function. If you have an early appendectomy, you have a much higher incidence of ulcerative colitis. And so there are all these t-cell immune modulators that we're just beginning to understand. So it may impact the gut biome, it may have different kind of immunological effects downstream.

But here's an advantage of ultrasound that CT will never be able to compete with. We're able to see these layers of the bowel wall. We can see the lamina propria, which you'll never be able to do. It's this hypo coic layer and it should be just about a millimeter. If it's three millimeters or greater, that's abnormal.

So this is what we see. The wall of the appendix is completely replaced by this lymphoid tissue and it compresses the echogenic submucosal layer and really attenuates the submucosa. So the striking feature of the wall is this thickened hypo coic lamina propria that is diagnostic of lymphoid hyperplasia. Lymphoid hyperplasia may or may not be associated with acute appendicitis. We sort of have to figure that out in just a moment when it is generalized, just think of the appendix as a large lymph node.

This child's head rotavirus and the lamin appropriate T-cell lymphocytes are just turned on. And if it's generalized throughout the entire appendix, even though the appendix is thickened, don't diagnose acute appendicitis. So when it's generalized throughout the whole appendix, that's just lymphoid hyperplasia.

Now, as you might suspect, if those lymphoid follicles hypertrophy, this will be non-compressible. It sort of increases the resistance and stiffness when we compress. But these could be up to seven millimeters. And this was called abnormal and this was completely normal other than lymphoid hyperplasia.

Now there's a proximal form of lymphoid hyperplasia that I just want to tell you about that does cause classically tip appendicitis. And so here we can see in this patient in the proximal, there is a little bit of dot flow that doesn't help us so much, but the lumen is compressed that echogenic luminal interface is compressed by this thickened hypo coic layer. The lamin appropriate but distally, the appendix is swollen, there's distal appendicitis with fluid around it. Here you can see the lymphoid hyperplasia obliterating the luma, and there's distal appendicitis in that patient.

And finally, another example of distal tip appendicitis marked thickening of the lame propria obliterating the proximal lumen. And there's distal both echogenic fluid and gas at the tip. Again, we're seeing this in an LPO position because was a retrocecal appendix. Notice that there's some gas in the appendix. And seeing intraluminal gas in the appendix may or may not be acute appendicitis. If there's secondary signs of appendicitis, it may be a gas forming infection.

So here's an example of distal appendicitis related to lymphoid hyperplasia.

Conclusion

So lots of new things that are happening with an old technique. And I hope that you'll reflect upon some of these things and incorporate them in your practice. And thanks to Sheila and the SR thank you very much.