0:00

Let's look at some prostate anatomy

0:02

and the axial projection on MRI.

0:05

This is a 62-year-old, and I think we'll

0:08

start someplace easy, right in the middle.

0:11

So this is a sagittal view,

0:13

just to get you oriented.

0:14

There's the coccyx in the back.

0:16

Here's the front of the patient.

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Heads up here.

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Feet are down here.

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Side view of the prostate.

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Let's get to the midline.

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So that's the midline.

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Now let's see where our axial projection is.

0:27

Almost smack dab in the middle of the prostate.

0:29

And that is the easiest spot.

0:32

We've got two major zones of the prostate.

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We've got a central gland, which is made

0:38

up of a central zone and transitional zone.

0:42

So, for all intents and purposes, I'll use

0:44

those terms interchangeably, even though

0:47

central gland consists of two components.

0:50

Now, this component, unfortunately,

0:53

as you get older, it gets bigger.

0:56

And it makes more PSA, Prostate-Specific Antigen.

0:59

So as you get older, your PSA is going to go up.

1:02

How fast it goes up depends on how fast this

1:06

gets bigger, and also what kind of tissue it is.

1:10

So if it gets bigger and it's benign tissue,

1:12

it's going to go up at a slower rate.

1:14

If it gets bigger and it's malignant tissue,

1:16

it's going to go up at a faster rate,

1:18

but no matter what, it's going to go up.

1:20

So as you get older, this portion of the prostate,

1:23

the central area or central zone of the prostate,

1:27

Properly said, the central gland is going to

1:30

enlarge, and it'll press on this outer part,

1:33

which is the peripheral zone of the prostate.

1:37

Now, when you're young, this may make

1:39

up as little as 5 percent or as much

1:41

as 20 or 25 percent of the gland.

1:44

But when you're older, that number goes up,

1:46

30, 35, 40, as much as 60 percent of the entire

1:50

gland as it presses against the peripheral zone.

1:53

Now, where do the cancers usually occur?

1:56

They usually occur in this area, this bright area

1:58

out here on this axial, water-weighted T2 image.

2:02

What percent?

2:03

About 70%.

2:05

And what are you looking for?

2:06

You're looking for nodules.

2:08

Now, as they say in the Wizard of Oz,

2:10

pay no attention to the man behind the curtain.

2:12

Well, pay no attention to these little tiny septa.

2:16

Things that are radially oriented from the

2:19

center to the outside are almost always benign.

2:22

If they're nodular or mass

2:24

like, then you've got to worry.

2:27

Now, a couple of other

2:28

housekeeping items at this level.

2:31

In the front, we've got some fat.

2:33

And that is known as the pre-fat.

2:35

Prostatic Space of Retzius.

2:38

Now also, don't pay too much attention

2:40

to this little bump right here, which is

2:42

some capsular swelling of the pubic bone,

2:44

completely unrelated to the prostate.

2:47

We have on the far left a T1-weighted image.

2:50

And at this level, we've got these small little

2:54

nubbins of signal surrounded by high signal fat.

2:57

So these two little grey dots with

2:59

fat around them on each side, at the

3:02

7 o'clock and 5 o'clock position.

3:04

These are the neurovascular bundles.

3:06

You want to see a clean, fatty,

3:09

bright contour on the T1-weighted image all the way

3:12

around these dots, like that one right there.

3:15

That tells you there is no

3:17

neurovascular bundle invasion.

3:21

Now staying simple at the mid-level

3:23

of the gland, we've also got two capsules.

3:28

We've got a surgical capsule, between

3:30

the central zone and the peripheral zone.

3:33

And then we have the anatomic capsule.

3:35

Now it's the anatomic capsule, when it's crossed,

3:39

that may preclude a patient from having a surgical

3:42

prostatectomy, because then it may be too late.

3:46

So some patients with borderline

3:47

capsular invasion, they may get surgery.

3:49

But this is a very important landmark.

3:53

The surgical capsule is valuable in another way.

3:56

Now tumors that arise in the

3:57

central zone are less common.

3:59

You're looking for something that looks like,

4:01

say, cream cheese on a bagel, kind of smears.

4:05

It's also called the charcoal sign.

4:07

When that charcoal sign crosses from

4:09

the central zone to the peripheral zone,

4:11

when it goes across this black band

4:13

right here, you've got big trouble.

4:16

Now you've got a malignancy.

4:18

You're crossing a critical boundary.

4:22

So let's stay with some other

4:23

adjacent structures at this level.

4:26

We've already discussed the periprostatic fat.

4:29

There's also some bright signal

4:31

intensity in the neurovascular bundle

4:33

region and around the prostate.

4:35

It's subtle, but that is the

4:37

periprostatic venous plexus.

4:40

And at certain levels, it'll be

4:41

more prominent than at other levels.

4:43

But on the T2-weighted image, it's bright.

4:46

Between the prostate and the

4:48

rectum is the prostatorectal space.

4:52

And volume-averaged on this axial with the

4:54

capsule, the reason the capsule looks a bit

4:56

thicker right there, it's because you're volume

4:58

averaging the Denonvilliers fascia between the

5:01

rectum and the prostate and the capsule together.

5:05

So that's another important crossing

5:07

landmark that you don't want to see violated,

5:10

especially the midline of the capsule.

5:13

Now, the posterior portion of the capsule indents

5:18

a little bit anteriorly, so it makes a

5:20

little bit of an inverted V, if you will.

5:24

Now let's go down.

5:26

So we're going to follow

5:27

the prostate more caudally.

5:29

And as we get more caudal, there is less of the

5:33

central gland, which consists, again, of the

5:35

transitional zone and central zone, and more

5:38

of the encircling, wrapping, peripheral zone.

5:42

Look how far down the peripheral zone goes.

5:46

Let's keep going, shall we?

5:47

The peripheral zone's a little more hyperintense.

5:49

It is enveloped by the levator sling,

5:52

a subject we talk about in detail.

5:55

In our pelvic floor assessment vignette.

5:58

And in the back, we have the rectum right here.

6:00

So let's keep going down further.

6:03

And as we go down further, things are converging.

6:05

The transitional and central zone are converging.

6:08

And then all the way down, they have converged.

6:10

This little nubbin of low signal

6:12

intensity, without any urine in

6:14

it, in the urethra, is the urethra.

6:17

Let's keep going down, and as we get down really

6:19

low, we start to run into some darker tissue.

6:23

Which consists of fibromuscular

6:24

stromal tissue anteriorly.

6:28

This is also known as the AS zone.

6:30

Now, this patient doesn't have a very

6:32

prominent anterior fibromuscular zone.

6:34

You can see a little bit of it here,

6:36

but it's going to be lentiform.

6:38

It'll be a little bit indented in the front.

6:40

And it's going to be lower in signal

6:42

intensity than the rest of the prostate gland.

6:45

In some patients, you may even see a

6:47

little raffae, right there,

6:49

running down the middle of the prostate.

6:51

Now, it's not uncommon in adults.

6:54

What's an adult?

6:56

Well, anybody over age 10 is an adult.

6:58

Not really.

6:59

But anybody over age 35 or 40 will

7:02

have some nodules in the prostate

7:04

because the prostate is getting bigger.

7:05

So what kind of nodules?

7:07

They can be nodules that contain, um, mucinous

7:10

material, or secretory material, like this one.

7:12

They can be bright nodules.

7:14

We used to biopsy these back in the old days.

7:17

No more.

7:18

Bright signal intensity is a good sign.

7:20

Or they can be round, gray nodules.

7:22

I don't see any here right now.

7:23

Here's another bright nodule.

7:25

But round, gray nodules don't bother me.

7:27

Unless they really tightly diffusion restrict.

7:31

They're markedly hypervascular with a washout,

7:33

but especially diffusion restriction,

7:36

or the nodule has a margin of irregularity,

7:39

and it starts to smear the adjacent tissues.

7:42

So a smooth, round, gray nodule, or even a

7:45

smooth, round, darker nodule in the central

7:49

portion of the gland doesn't bother me at all.

7:53

Now let's work our way proximal.

7:55

We're going north.

7:57

Let's go up a bit towards the prostate base.

8:01

And at the prostate base,

8:02

we see the seminal vesicles.

8:05

And a little bit of secretory

8:07

material in the left ductus deferens.

8:11

Let's talk a little bit

8:11

about the seminal vesicles.

8:13

There's a fair amount of variability

8:15

in the signal of the seminal vesicles

8:17

as we get to the prostate base.

8:19

And that's because the secretions

8:22

may be inspissated or dried out.

8:24

So if they're inspissated or dried out,

8:26

then they're going to be grayer or darker.

8:29

Typically in younger individuals, you'll

8:31

have a fair amount of secretory material.

8:33

You'll have an acinar gland pattern,

8:36

so that each portion of the gland looks like

8:38

this little irregular, hexagon

8:41

right there, and then they kind of fit

8:43

together one right next to the other.

8:45

So the younger the patient, the more likely

8:47

you are to have homogeneous bilateral high

8:50

signal intensity in the seminal vesicle.

8:54

Now let's go back to the base.

8:56

At the base of the prostate,

8:58

we've got quite a bit.

9:00

of central gland material, and only

9:04

when we come down off the base do

9:05

we see much of the peripheral zone.

9:08

So as we come down, the peripheral

9:09

zone assumes greater prominence.

9:12

As we go up, the hyper intense peripheral zone

9:15

assumes a little bit less, less prominence.

9:18

That's not to say you don't get cancers

9:20

here, because you certainly do, and they're

9:22

more easily seen in the coronal projection.

9:25

Let's take on a few additional

9:27

anatomic structures.

9:29

For instance, next door we've got the obturator

9:32

internist canal, anterior, and in fact,

9:36

anterosuperior on the sagittal, but anterior

9:39

and superior on the axial is the bladder.

9:43

You have to assess the bladder size,

9:46

the thickness of the wall, whether it's ated.

9:50

In other words, these small

9:51

nubbins of high signal intensity.

9:54

that penetrate the inner lumen of

9:56

the bladder, but don't go through it.

9:58

So we call this bladder

9:59

hypertrophy with cellulation.

10:02

If one of these penetrates through and fills

10:05

with urine, then we call that a diverticulum.

10:09

Now while you're in the neighborhood, you've

10:10

got a lot of other structures hanging out.

10:12

You've got your hips on either side.

10:14

Don't forget to look at those

10:15

in the axial projection.

10:16

On the film edge, this patient happens

10:18

to have a cyst arising from the left hip,

10:21

and has some arthrosis in the right hip.

10:23

Both hips in the back, we've got the

10:25

rectum and the pararectal space.

10:28

We're also gonna look at the

10:29

character of the rectal wall.

10:32

And when we get down low on the T2

10:33

weighted image, we're gonna look for fissures

10:36

in anal sinus tracts and microabscesses.

10:40

So that concludes.

10:42

Our view of the prostate and the

10:44

axial material, and the axial projection.

10:47

We're not going to talk about the erectile

10:49

tissue, because we're focusing purely on

10:51

the prostate right now, and you've seen the

10:53

difference between the apex, the inferior

10:55

portion of the gland, the mid portion

10:58

of the gland, and the base of the gland.

11:02

Let's move on to another projection.

11:04

Let's try coronal, shall we?