0:00

I'm Dr. P, back discussing pediatric renal

0:01

3 00:00:04,210 --> 00:00:06,529 masses and their differential diagnosis.

0:06

I have on the left a gradient echo TR about 100

0:10

to 150, so longer than usual, very short TE.

0:14

So a type of, uh, spoiled gradient echo in phase.

0:19

And on the right, I've got a T2

0:20

spin echo without fat suppression.

0:23

So the fact that this portion of the kidney and

0:25

capsule are very dark on the T2, but not very bright

0:30

on the T1, suggests and supports the diagnosis

0:34

of a capsular bleed or hemorrhage, which is going

0:37

to push you towards and away from some lesions.

0:41

On the bottom, we've got a more solid

0:43

appearing renal mass, multi lobulated,

0:45

but nothing in the opposite kidney.

0:47

Let's scroll it to be sure, because that's

0:49

one of our most important search patterns.

0:51

And we can see an adrenal gland on the left, The

0:54

adrenal gland on the right, not so prominent,

0:57

because neuroblastoma we'd want to exclude, but our

1:00

lesion is in the inferior pole of the kidney, so

1:03

neuroblastoma not a strong consideration, especially

1:07

with sparing in the region of the right adrenal

1:09

gland, which we'll see better in the axial projection.

1:11

Lack of crossing of the midline.

1:13

Lack of skeletal metastases.

1:16

And then we know that neuroblastoma

1:17

calcifies more often than Wilms tumor.

1:20

But that's a very important

1:21

differential diagnostic consideration.

1:24

Let's scroll in and out of the lesion.

1:25

And we really get into a more

1:27

solid component of the lesion.

1:30

And we're seeing foci of hemorrhage within the lesion.

1:33

There were some scant calcifications

1:36

seen on CT which occur about the midline.

1:38

15 percent of the time, but I want to emphasize

1:41

that age is the most important consideration

1:44

when formulating a differential diagnosis, and

1:47

Wilms tumor is the most likely diagnosis in the

1:50

pediatric population, especially under age 5 or 10.

1:55

Now, renal vein invasion is also important.

1:58

A strong, uh, differential diagnostic separator.

2:03

Here is your inferior vena

2:04

cava with flow void on the T2.

2:06

And I like the T2 for this purpose.

2:08

I don't need contrast, uh, to clear the renal vein.

2:12

The renal vein is compressed, but it is not

2:14

invaded, even though the tumor is right next to it.

2:17

Perhaps a little nubbin.

2:18

Right there is just starting to enter the renal vein.

2:22

But remember, you can get renal vein

2:24

invasion with renal cell carcinoma.

2:26

And this is the second most

2:27

common renal tumor of childhood.

2:30

Renal cell carcinoma becomes more common than

2:32

Wilms tumor during the second decade of life.

2:36

And Wilms tumor can occur in fetuses and neonates.

2:39

But in this age group, congenital mesoblastic

2:43

nephroma, and we'll use the abbreviation

2:45

CMN from here on out, is more likely.

2:49

Now, there are some other less common renal tumors

2:51

that occur in young children, and they're generally

2:54

indistinguishable from Wilms tumor at imaging alone.

2:58

But, there may be some features that

3:00

suggest one diagnosis over the other.

3:02

One of these is clear cell sarcoma, also known

3:06

as CCSK, clear cell sarcoma of the kidney.

3:11

These also show early skeletal metastases,

3:13

and our skeleton is nice and clean.

3:16

And, um, the skeleton is not a common

3:19

site early on for Wilms tumor.

3:21

Another one is the rhabdoid tumor.

3:23

Now this has an established association with

3:25

brain tumors, especially in the posterior fossa.

3:28

I haven't shown you any.

3:30

In addition, the finding of subcapsular hemorrhage,

3:32

which we do have in this case, suggests rhabdoid tumor,

3:36

but still, Wilms tumor is so much more common that

3:40

we would still favor the diagnosis of Wilms tumor.

3:44

An additional important differential diagnostic

3:46

consideration in a child is pyelonephritis.

3:50

Now yes, pyelonephritis is a hyperemic state, but

3:53

it's still not as vascular as the main kidney.

3:56

Here's the renal parenchyma.

3:58

So if we were to enhance pyelonephritis, we

4:01

might see a cold area, and it might be, uh,

4:04

striated or triangular, not cold, but less

4:08

vascular than the rest of the renal parenchyma.

4:11

So, you might have an episode of nephritis that is

4:14

hypovascular relative to the normal renal parenchyma.

4:18

And that is a little confusing because

4:20

the kidney is quite a vascular organ.

4:24

Another consideration would be a renal abscess.

4:26

Now, in a renal abscess, you're

4:28

going to get usually a single cavity.

4:30

Occasionally, a cavity can be multiloculated.

4:33

It's going to be pretty bright

4:35

on the T2-weighted image, although sometimes in the

4:38

center of an abscess, it'll be a little bit darker due

4:42

to the peroxidases that cause, that cause shortening

4:46

of T2 relaxivity, a so-called paramagnetic phenomenon.

4:50

But probably the most helpful thing is the child has

4:53

flank pain, a fever, and white cells in the urine.

4:57

So, real basic, basic stuff is going to give you the

5:01

right tip-off to the diagnosis of a renal infection.

5:05

Although Wilms tumor is the most common

5:07

pediatric renal tumor, and I'll say it again

5:09

and again for you board takers, it can be

5:12

indistinguishable from cellular, uh, CMN at imaging.

5:17

CMN is more common in young infants.

5:21

On the other hand, if there are bilateral

5:23

tumors, venous invasion, or pulmonary metastases,

5:27

which Wilms is prone to do, then Wilms is

5:29

overwhelmingly a more likely diagnosis.

5:33

How about CCSK?

5:34

We've already talked briefly about

5:36

clear cell sarcoma of the kidney.

5:40

Um, this is similar to the cellular

5:42

subtype of CMN with multiple cystic foci,

5:45

but CMN is more common in young infants.

5:50

Another very rare condition is known as

5:52

ORTI, or ossifying renal tumor of infancy.

5:57

ORTI typically demonstrates calcified osteoid matrix.

6:00

If we, uh, take away our color here for a minute and

6:03

go back to our areas of low signal intensity.

6:07

Osteoid matrix doesn't look like this.

6:09

It's cloudy.

6:10

It's irregular.

6:11

It may be a little whirly or

6:13

swirly, but not popcorn-like.

6:14

This is blood.

6:16

So, you wouldn't want to confuse

6:17

this with the osteoid matrix of ORTI.

6:21

And then we come back to the all-important

6:23

neuroblastoma at the very beginning where we said

6:26

that we like our neuroblastoma to arise from somewhere

6:29

high near the adrenal gland and invade the

6:31

kidney rather than come directly from the kidney.

6:35

And we've also given you some other key

6:37

features to differentiate neuroblastoma

6:40

from Wilms tumor in this five-year-old.

6:42

Let's move on, shall we?

6:43

Dr. P out.