0:00

Here we have a contrast-enhanced CT scan of

0:03

the abdomen pelvis, and as we come down, we

0:05

can see that the liver and spleen look good.

0:08

There's a nice pancreas as well, but

0:10

already in the retroperitoneum we're seeing

0:11

a little difference between the kidneys.

0:13

But I'm going to ignore that for now and go through the

0:15

rest of my search pattern where I would look at the GI

0:18

tract to make sure there's no evidence of obstruction.

0:20

Look at that appendix.

0:21

It couldn't be more beautiful.

0:23

Peeking out at us, and I would say that,

0:24

you know, I don't see any obstruction

0:25

or any major problems in the GI tract.

0:28

Once I see that there's a problem with the

0:30

kidneys, I like to go with the coronals

0:33

because I think on the coronals you can

0:34

really see the difference between the kidneys.

0:37

Back when I was a resident, ye—

0:39

the long days ago, we didn't have.

0:42

A lot of the templates that you all use for

0:44

dictating, and we used to always say the same thing

0:47

when we were dictating the kidneys and it just

0:48

rings in my head like a bad dream all the time.

0:51

And it was: the kidneys enhance symmetrically without

0:53

evidence of mass lesions or signs of hydronephrosis.

0:56

So would you say that these

0:58

kidneys enhance symmetrically?

1:00

No.

1:01

Right.

1:01

They are in different phases of contrast enhancement.

1:04

Here on the right we have a beautiful nephrographic

1:07

phase kidney, meaning that the kidney is very

1:09

homogeneous in attenuation, and there has been time

1:12

during that portal venous phase for contrast to be both

1:15

in the cortex and leak into those medullary cavities.

1:18

So this would be the normal appearance

1:20

of a kidney at this phase of contrast.

1:22

Notice on the left that we have a very stark

1:25

difference between the cortex and medullary pyramids.

1:28

This is that—

1:29

corticomedullary phase, which would be an

1:31

early enhancing appearance of the kidney,

1:33

but what's causing that? Look at this kidney.

1:36

You can see beautiful hydronephrosis where

1:38

we have dilatation of the renal collecting

1:40

system, and no surprise in this case.

1:43

As we come down, we see a very large renal

1:45

calculus at the level of the ureteropelvic

1:49

junction between the ureter and the pelvis.

1:51

So this is an obstructing renal calculi.

1:54

Why is there a change in enhancement?

1:56

That's because the pressure in those

1:58

tubules is much higher as a result of

2:00

that outlet obstruction of the urine.

2:03

So that kidney cannot go through its normal

2:05

phase of contrast, where it will take up the

2:09

contrast and then excrete it into the tubules.

2:11

So you'll find this asymmetric enhancement as a common

2:15

problem in patients who have obstructive uropathy.

2:17

Would we normally give contrast

2:19

to a patient for renal stones?

2:20

People always ask me that.

2:21

I would say you don't need

2:23

contrast for a renal stone case.

2:25

We oftentimes do them without contrast,

2:27

but because sometimes it's not as

2:28

defined what the patient comes in with.

2:30

With renal colic, we frequently will see

2:32

renal stones on contrast-enhanced CT scans.

2:35

So here we have a delayed nephrogram,

2:38

a delay of enhancement of a left kidney

2:40

secondary to hydronephrosis as a result of

2:43

a very large obstructing renal calculus.