Interactive Transcript
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Let's look at some prostate anatomy
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and the axial projection on MRI.
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This is a 62-year-old, and I think we'll
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start someplace easy, right in the middle.
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So this is a sagittal view,
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just to get you oriented.
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There's the coccyx in the back.
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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.
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Almost smack dab in the middle of the prostate.
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And that is the easiest spot.
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We've got two major zones of the prostate.
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We've got a central gland, which is made
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up of a central zone and transitional zone.
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So, for all intents and purposes, I'll use
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those terms interchangeably, even though
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central gland consists of two components.
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Now, this component, unfortunately,
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as you get older, it gets bigger.
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And it makes more PSA, Prostate-Specific Antigen.
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So as you get older, your PSA is going to go up.
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How fast it goes up depends on how fast this
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gets bigger, and also what kind of tissue it is.
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So if it gets bigger and it's benign tissue,
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it's going to go up at a slower rate.
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If it gets bigger and it's malignant tissue,
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it's going to go up at a faster rate,
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but no matter what, it's going to go up.
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So as you get older, this portion of the prostate,
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the central area or central zone of the prostate,
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Properly said, the central gland is going to
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enlarge, and it'll press on this outer part,
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which is the peripheral zone of the prostate.
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Now, when you're young, this may make
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up as little as 5 percent or as much
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as 20 or 25 percent of the gland.
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But when you're older, that number goes up,
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30, 35, 40, as much as 60 percent of the entire
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gland as it presses against the peripheral zone.
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Now, where do the cancers usually occur?
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They usually occur in this area, this bright area
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out here on this axial, water-weighted T2 image.
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What percent?
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About 70%.
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And what are you looking for?
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You're looking for nodules.
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Now, as they say in the Wizard of Oz,
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pay no attention to the man behind the curtain.
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Well, pay no attention to these little tiny septa.
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Things that are radially oriented from the
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center to the outside are almost always benign.
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If they're nodular or mass
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like, then you've got to worry.
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Now, a couple of other
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housekeeping items at this level.
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In the front, we've got some fat.
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And that is known as the pre-fat.
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Prostatic Space of Retzius.
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Now also, don't pay too much attention
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to this little bump right here, which is
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some capsular swelling of the pubic bone,
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completely unrelated to the prostate.
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We have on the far left a T1-weighted image.
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And at this level, we've got these small little
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nubbins of signal surrounded by high signal fat.
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So these two little grey dots with
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fat around them on each side, at the
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7 o'clock and 5 o'clock position.
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These are the neurovascular bundles.
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You want to see a clean, fatty,
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bright contour on the T1-weighted image all the way
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around these dots, like that one right there.
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That tells you there is no
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neurovascular bundle invasion.
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Now staying simple at the mid-level
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of the gland, we've also got two capsules.
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We've got a surgical capsule, between
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the central zone and the peripheral zone.
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And then we have the anatomic capsule.
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Now it's the anatomic capsule, when it's crossed,
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that may preclude a patient from having a surgical
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prostatectomy, because then it may be too late.
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So some patients with borderline
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capsular invasion, they may get surgery.
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But this is a very important landmark.
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The surgical capsule is valuable in another way.
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Now tumors that arise in the
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central zone are less common.
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You're looking for something that looks like,
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say, cream cheese on a bagel, kind of smears.
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It's also called the charcoal sign.
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When that charcoal sign crosses from
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the central zone to the peripheral zone,
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when it goes across this black band
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right here, you've got big trouble.
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Now you've got a malignancy.
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You're crossing a critical boundary.
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So let's stay with some other
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adjacent structures at this level.
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We've already discussed the periprostatic fat.
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There's also some bright signal
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intensity in the neurovascular bundle
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region and around the prostate.
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It's subtle, but that is the
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periprostatic venous plexus.
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And at certain levels, it'll be
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more prominent than at other levels.
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But on the T2-weighted image, it's bright.
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Between the prostate and the
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rectum is the prostatorectal space.
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And volume-averaged on this axial with the
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capsule, the reason the capsule looks a bit
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thicker right there, it's because you're volume
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averaging the Denonvilliers fascia between the
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rectum and the prostate and the capsule together.
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So that's another important crossing
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landmark that you don't want to see violated,
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especially the midline of the capsule.
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Now, the posterior portion of the capsule indents
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a little bit anteriorly, so it makes a
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little bit of an inverted V, if you will.
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Now let's go down.
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So we're going to follow
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the prostate more caudally.
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And as we get more caudal, there is less of the
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central gland, which consists, again, of the
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transitional zone and central zone, and more
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of the encircling, wrapping, peripheral zone.
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Look how far down the peripheral zone goes.
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Let's keep going, shall we?
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The peripheral zone's a little more hyperintense.
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It is enveloped by the levator sling,
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a subject we talk about in detail.
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In our pelvic floor assessment vignette.
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And in the back, we have the rectum right here.
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So let's keep going down further.
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And as we go down further, things are converging.
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The transitional and central zone are converging.
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And then all the way down, they have converged.
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This little nubbin of low signal
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intensity, without any urine in
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it, in the urethra, is the urethra.
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Let's keep going down, and as we get down really
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low, we start to run into some darker tissue.
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Which consists of fibromuscular
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stromal tissue anteriorly.
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This is also known as the AS zone.
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Now, this patient doesn't have a very
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prominent anterior fibromuscular zone.
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You can see a little bit of it here,
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but it's going to be lentiform.
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It'll be a little bit indented in the front.
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And it's going to be lower in signal
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intensity than the rest of the prostate gland.
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In some patients, you may even see a
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little raffae, right there,
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running down the middle of the prostate.
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Now, it's not uncommon in adults.
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What's an adult?
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Well, anybody over age 10 is an adult.
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Not really.
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But anybody over age 35 or 40 will
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have some nodules in the prostate
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because the prostate is getting bigger.
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So what kind of nodules?
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They can be nodules that contain, um, mucinous
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material, or secretory material, like this one.
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They can be bright nodules.
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We used to biopsy these back in the old days.
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No more.
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Bright signal intensity is a good sign.
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Or they can be round, gray nodules.
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I don't see any here right now.
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Here's another bright nodule.
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But round, gray nodules don't bother me.
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Unless they really tightly diffusion restrict.
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They're markedly hypervascular with a washout,
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but especially diffusion restriction,
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or the nodule has a margin of irregularity,
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and it starts to smear the adjacent tissues.
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So a smooth, round, gray nodule, or even a
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smooth, round, darker nodule in the central
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portion of the gland doesn't bother me at all.
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Now let's work our way proximal.
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We're going north.
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Let's go up a bit towards the prostate base.
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And at the prostate base,
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we see the seminal vesicles.
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And a little bit of secretory
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material in the left ductus deferens.
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Let's talk a little bit
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about the seminal vesicles.
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There's a fair amount of variability
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in the signal of the seminal vesicles
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as we get to the prostate base.
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And that's because the secretions
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may be inspissated or dried out.
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So if they're inspissated or dried out,
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then they're going to be grayer or darker.
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Typically in younger individuals, you'll
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have a fair amount of secretory material.
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You'll have an acinar gland pattern,
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so that each portion of the gland looks like
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this little irregular, hexagon
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right there, and then they kind of fit
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together one right next to the other.
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So the younger the patient, the more likely
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you are to have homogeneous bilateral high
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signal intensity in the seminal vesicle.
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Now let's go back to the base.
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At the base of the prostate,
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we've got quite a bit.
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of central gland material, and only
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when we come down off the base do
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we see much of the peripheral zone.
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So as we come down, the peripheral
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zone assumes greater prominence.
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As we go up, the hyper intense peripheral zone
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assumes a little bit less, less prominence.
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That's not to say you don't get cancers
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here, because you certainly do, and they're
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more easily seen in the coronal projection.
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Let's take on a few additional
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anatomic structures.
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For instance, next door we've got the obturator
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internist canal, anterior, and in fact,
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anterosuperior on the sagittal, but anterior
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and superior on the axial is the bladder.
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You have to assess the bladder size,
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the thickness of the wall, whether it's ated.
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In other words, these small
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nubbins of high signal intensity.
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that penetrate the inner lumen of
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the bladder, but don't go through it.
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So we call this bladder
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hypertrophy with cellulation.
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If one of these penetrates through and fills
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with urine, then we call that a diverticulum.
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Now while you're in the neighborhood, you've
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got a lot of other structures hanging out.
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You've got your hips on either side.
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Don't forget to look at those
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in the axial projection.
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On the film edge, this patient happens
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to have a cyst arising from the left hip,
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and has some arthrosis in the right hip.
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Both hips in the back, we've got the
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rectum and the pararectal space.
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We're also gonna look at the
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character of the rectal wall.
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And when we get down low on the T2
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weighted image, we're gonna look for fissures
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in anal sinus tracts and microabscesses.
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So that concludes.
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Our view of the prostate and the
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axial material, and the axial projection.
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We're not going to talk about the erectile
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tissue, because we're focusing purely on
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the prostate right now, and you've seen the
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difference between the apex, the inferior
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portion of the gland, the mid portion
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of the gland, and the base of the gland.
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Let's move on to another projection.
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Let's try coronal, shall we?
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