Membranous Urethra
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Let's talk about the membranous urethra,
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which is one of the components, the inferior
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component, of the posterior urethra, which
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means there's got to be an anterior urethra,
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which begins at the bulb and goes into
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the penis and then the external meatus.
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Set that aside again and focus on the membranous
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urethra, which is the continuation or lies
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just inferior to the lower prostatic urethra.
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And here it is in the axial projection.
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These are all 2D, 3-millimeter, heavily
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water-weighted T2 fast spin echo images.
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So in the coronal projection, this is a
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direct coronal orthogonal, sagittal, and axial.
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We see the urethra coming down towards this dark
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U-shaped area, more inferiorly, between these
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two muscle bellies, the membranous urethra.
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Now, the membranous urethra in the axial
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projection is only about one centimeter long.
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So, if you're using three-millimeter cuts, you're
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only going to see it for three slices in total.
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In the membranous segment is the external
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sphincter and also two paired Cowper's glands.
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Can you see the Cowper's glands?
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Sometimes you can.
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For instance, on this coronal image, there is
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the right Cowper's gland opening just adjacent
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to the membranous urethra on the right.
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And it does communicate with
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the urethra, although we don't have the
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resolution to see that communication.
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In the axial projection, I'm gonna make
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it a little bigger. In the membranous
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urethra, you can divide it up into a
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brighter central area, which is white.
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Now, all you have to remember is white,
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dark, white, dark for the zones
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down in the membranous urethra.
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So white in the middle, central zone.
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Then you have an inner area that you
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can barely see, it's pretty thin, dark.
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Then you have a middle area which is
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a little bit brighter and thicker.
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Brighter and then dark around the periphery.
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So white, dark, white, dark.
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Central, inner, middle, outer.
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And that, my friends, is the membranous urethra.
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
John F. Feller, MD
Chief Medical Officer, HALO Diagnostics. Medical Director & Founder, Desert Medical Imaging. Chief of Radiology, American Medical Center, Shanghai, China.
HALO Diagnostics
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