Interactive Transcript
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Let's look at the axial T1-weighted or fat-
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weighted appearance of the prostate on MR.
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I've got the axial
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T2-weighted up for a comparison.
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The T1-weighted image is not meant to help
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you evaluate the locus or to detect cancers
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and to put them in their proper zone.
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Its main function is to evaluate the periprostatic
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fat and the neurovascular bundles at 5 o'clock
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and 7 o'clock, which should be surrounded by fat.
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So, let's scroll it a little bit.
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And yeah, in some locations, it may be a little
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tough to, to separate or distinguish them.
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But there's no mass effect.
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The fat is pretty symmetric on both sides.
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Now, each vessel isn't going to be
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exactly identical to the other side.
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So if you're very OCD, then you're
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going to, you're going to tend to
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overcall invasion of this area.
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But, you know, if you're going to call invasion,
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you should have a mass that has capsular contact.
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And almost always, that mass that has
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capsular contact is somewhere between
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one and a half to two centimeters long.
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So if you simply see a little bit of asymmetry
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there, and there's no mass present, that's silly.
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Don't make that mistake.
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So it's not going to be exactly identical
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from side to side, and you'll notice that the
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signal is a little darker on the left than the
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right, and perhaps the flow rates are a little
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faster on the left than the right, which brings
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me to another role of the T1-weighted image.
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We've talked about the importance of fat,
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capsular invasion, including the pre-prostatic
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space of Retzius, which we'll inspect, but
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also the T1-weighted image, especially
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if they're, they're a little bit thinner,
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can help you look for nodes just like CT.
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know, I see nodules on MRI all the time."
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How do I know whether something
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is a nodule or a node?
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That takes a little bit of experience,
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but not a tremendous amount.
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There are a couple of ways.
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First of all, nodes are not tubular.
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So if the structure you're looking at
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is tubular, like that one, not a node.
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Nodes are going to be gray.
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So if the structure that you're looking
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at is very hyperintense or white,
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like that, it's not going to be a node.
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You know, it's probably going to be
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flow, like that flow right there.
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So signal intensity is also going to help you.
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Nodes that are involved by prostate
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metastasis tend to be gray, round,
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plump, and have no fatty hila.
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Size criteria helpful, about 1 centimeter.
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But morphology, plumpness,
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the absence of the fatty hila.
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Isolation, a node that's 1.2 centimeters
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that's round and gray,
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sitting all by itself in the iliac
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chain, that is a worrisome thing.
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Now it's very helpful to go back and
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forth between, say, the T1 and the T2,
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and that's why I have the T2 up here.
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For instance, this structure right
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here is tubular, okay, that's easy.
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But let's say it wasn't tubular.
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Let's say it was circuitous, like a vessel,
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and it didn't have a straight course.
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So it's hard to tell that it
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really is a linear structure.
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Well, you look over here and you see this
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round on the outside and gray on the inside?
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That is slow flow in a vessel with
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faster flow in the center of the vessel.
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So that ring-like appearance
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is another method you can use
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that tells you you're not dealing with a node.
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Now, don't forget to look at the, the
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obturator chain nodes and the obturator
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canal in a patient with prostate cancer.
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You, you, you do have a, a, a complement
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of an artery, a vein, and a nerve in there.
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Sometimes you may have some small
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nodes in there that are undersized,
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maybe 3 or 4 millimeters at best.
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But you shouldn't have anything that
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approaches a centimeter in the obturator canal.
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So that's how you use the T1-weighted image
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to look for neurovascular bundle invasion,
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anatomic capsular crossing into the surrounding
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periprostatic fat, and looking for nodes.
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Don't forget, the T1-weighted image is a
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very reliable, helpful sequence in prostate
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cancer to look for bone mets, right?
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The fat is white, and prostate cancer tends
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to be sclerotic; sclerosis is dark, so dark
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against the background of white, especially with
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round or irregular shape, easy in most cases
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of metastatic prostate carcinoma to the bone.
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That concludes our discussion of the axial
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T1-weighted image on MR and its role.
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