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Now we're going to talk a bit about imaging

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the kidneys, the hardest working organ in the body,

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and we're going to talk about the normal appearance

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of the kidneys on various phases of contrast.

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Remembering, you know, the kidneys

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are paired organs that are found in the

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retroperitoneum, in that perirenal space.

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There's a renal cortex, and then

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there's the medullary pyramids.

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These medullary pyramids are made up of the

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nephrons with the nephron loops, or loops of

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Henle, that come down deep into the papilla.

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Those are the excretory portions of the

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loops, and then back up into the cortex.

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I'm sure you can kind of remember from medical

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school, like sodium channels and blah, blah, blah.

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But since we don't have to remember

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this kind of homeostasis, we are.

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The happy people in medicine, but definitely we need

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to realize that the cortex will enhance first, and

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then the contrast will be excreted, as all contrast is

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excreted into the urinary tract, and then leaves our

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body through the urine into those medullary pyramids.

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This is that early arterial phase where

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you have that corticomedullary phase

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of imaging, so this would be that normal.

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Appearance, we're going to see the normal fat

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of the renal hilum, and we may see a very

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delicate, nice collecting system as well.

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Numerous vessels come in, both the arteries

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and veins, which we'll see in different cases.

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So as we image through the patient at different

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time points, we will see the beauty of renal

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physiology as it can be seen on radiology.

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And you'll see that 32-second delay, we'll

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have that corticomedullary phase of

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imaging once you get to about 70 seconds.

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Contrast should be excreted into the tubules,

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making this beautiful nephrographic

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phase, or homogeneous phase of imaging.

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And then when you take a little bit later,

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you get the excretory phase of imaging where

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you actually have condensed, uh, contrast

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within the, um, urinary collecting system.

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I frequently say when the ureters are in play,

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get delays.

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So anytime you're concerned about a ureteric injury,

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maybe the patient's coming from, um, an iatrogenic

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imperfect, a situation where they think they

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might have nicked the ureter down in the pelvis,

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you want to get a pretty good delay on those cases.

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So here's back to our patient.

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Here's back to our patient where

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we have that asymmetric nephrogram.

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With that obstructing renal calculus up here in

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the left upper quadrant, again, you know, we're

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not usually trying to image our renal stone

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protocols with contrast, but on the flip side,

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our patients are coming through the ER so fast

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right now that the confidence interval can be

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decreased from what it used to be because

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frequently our patients are getting a

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CT scan even prior to the urinalysis.

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So it used to be that if you had blood in the

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urine and you had flank pain or upper quadrant

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pain, they would assume you had a stone.

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And we get an I-minus CT scan.

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But honestly, I think our CT scans are

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frequently faster than urine today.

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We like to say that if you have a 90

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to 95% confidence interval, maybe the

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patient's had a stone before or the like.

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Then you would want to do a non-contrast CT scan.

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Or maybe you just start with an ultrasound.

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For hydro, though, our referring clinicians

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are always a little skeptical of that.

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But if you are at all ambiguous of

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your diagnosis, we prefer contrast.

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It just takes a black and white television to a color

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television so that if your patient has something

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other than a renal stone, we have access to that

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physiology and a better imaging with contrast.

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Now, what are the locations of impacted stones?

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There's very many different locations, but

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these are kind of the classics, ureteropelvic

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junction up here at the top of the ureter

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where the renal pelvis drains into the ureter.

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Then we frequently will see stones

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impact at the pelvic brim, or as that

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ureter comes over the iliac vasculature.

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Here's the iliac vein, here's the iliac artery,

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and as a result, there's a little bit of stenosis

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there in medical school during

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anatomy.

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I remember learning that we call this the water

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going over the bridge because the urine is the

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water going over the bridge of the vessels.

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And that is a relative difficulty for that

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little stone to get over that bridge there.

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And then most frequently we actually see the

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stones at the ureterovesical junction

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where the ureter comes into the bladder.

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Uh, and frequently they’re just on their way out there.

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I think maybe a six-pack of

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Coors Light, and this would pass.

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Light beer is a great diuretic.

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It’s actually one of the ways to

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get, uh, small stones to move on.

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Not necessarily condoned in the hospital environment,

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but good for you to know, maybe of major importance.

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You always want to measure renal

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stones on axial images in bone windows.

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I’m going to repeat that, and you can repeat with me.

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I’m always going to measure my renal

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stones on axial images in bone windows.

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Why is that?

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That’s because all of the literature about whether or

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not there’s a probability of a stone passing without

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intervention, i.e., just with fluid hydration, is done on

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literature back when axial images

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were kind of the only thing.

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Plus, you can imagine that really it’s how big

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the stone is in this dimension, not how long it

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is, because the length of it, you know, that’s

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just going to go down the tube of the ureter.

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So it’s really how wide the stone is

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going down the tube that will make

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whether or not the patient will be able to pass that

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stone in our institution, or in all institutions.

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Ninety percent of stones will pass under five millimeters.

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Frequently, patients with under five-millimeter

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stone will be treated with fluid, and

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those who have stones over five millimeters

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will usually get a urological consult.

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So my residents are oftentimes friends with the

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urologist and are always apprehensive to measure

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that stone at six millimeters, which I understand.

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But I think if we just do it by convention, which is

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bone windows.

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Axial imaging will all have

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a, a good set of rules there.

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Okay, so here’s a patient with

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hydronephrosis on ultrasound.

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These are those beautiful pyramids in a

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patient who’s young and has a nice corticomedullary

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junction on the ultrasound here.

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So that’s normal.

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Here’s a delicate, small collecting system

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without dilatation, as opposed to the

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contralateral side where we have that colic.

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Fluid urine within a dilated collecting system.

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You can see, um, the blunting of the calyx here.

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So this would be a consistent with a left-sided

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obstruction, likely secondary to a stone.

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Our technologist finds the stone

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here that is to be, give major kudos.

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These can be very hard to image, so that is

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an echogenic stone in that very distal ureter.

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The individual shows us the twinkle artifact.

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That’s frequently something your technologist

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show you an image of when they have a stone

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that didn’t have great posterior shadowing.

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Um, that’s another indication that

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indeed there is a stone there.

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It’s not soft tissue.

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There’s physics to this.

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Maybe, I don’t really a hundred percent remember it,

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but when you see twinkle artifact, which is just this

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kind of heterogeneous, both blue and red, behind a

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dense structure, that is indicative of it being a stone.