Membranous urethra !

The membranous urethra is the short part of the male urethra just below the prostate; the external sphincter around it gives voluntary control of urine.

Official name: Intermediate part of male urethra

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What it is

The short (about 1-2 cm), narrowest and least stretchy part, from the apex of the prostate through the perineal membrane, surrounded by the external urethral sphincter.

What it does

Where voluntary control of urine happens; after a radical prostatectomy it is joined to the bladder neck, and keeping its length helps continence.

Key facts

Where: About 1–2 cm from the prostatic apex through the deep perineal pouch and perineal membrane; the narrowest and least distensible part after the external meatus
Attaches: Surrounded by the external urethral sphincter (striated, pudendal nerve S2–S4); bulbourethral glands on each side
Function: Voluntary continence; torn in pelvic fracture (blood at the meatus, high-riding prostate), so the injury is ruled out before a catheter is passed

Relations

Above: Prostatic apex and the prostatic urethra
Below: Perineal membrane, below which it becomes the bulbar part of the spongy urethra
Lateral: Bulbourethral glands, within the deep perineal pouch
In front: Deep dorsal vein of the penis passing under the pubic symphysis to the prostatic venous plexus
Behind: Perineal body and the rectum; a rectourethral fistula is a rare complication of prostate surgery or radiation

How to find it

Sits at the level of the perineal membrane, just behind and below the pubic symphysis, wrapped by the external urethral sphincter. On digital rectal examination the bulb and this segment are met first in front, and the prostate a few centimetres higher; after a pelvic fracture a prostate that feels high or is not felt classically points to a tear here.

On imaging

When injury is suspected, a retrograde urethrogram is done before any urethral catheter: contrast leaking at this level confirms a posterior injury and shows whether it is partial or complete. Leak above the perineal membrane fills the pelvis; leak below it reaches the perineum.

Common problems

The part most easily torn in a pelvic fracture.

How it is diagnosed

Urine tests and swabs; urine flow test; urethrogram or a scope (urethroscopy).

Treatment

Antibiotics for urethritis; widening or surgical repair (urethroplasty) of a stricture.

Clinical notes

In complete disruption, urine is diverted with a suprapubic catheter; the gap heals with scar and is usually repaired later by urethroplasty
The usual point of resistance when a catheter is passed in a tense patient, as the sphincter contracts around it
Radical prostatectomy joins it to the bladder neck; the length kept and the health of the external urethral sphincter largely decide continence

Development

Comes from the pelvic part of the urogenital sinus (endoderm), as does the prostatic urethra above it.

Bladder and urethral injury

Test yourself

Think of the answer, then tap the question to see it.

Which part of the male urethra is sheared in pelvic ring fractures, and why?

The membranous urethra, fixed by the perineal membrane and the prostatic attachments above it.

Which signs suggest membranous urethral injury, and what test comes before any catheter?

Blood at the meatus and a high-riding prostate; a retrograde urethrogram is done first.

Where do urine and blood spread after a membranous urethral injury with an intact perineal membrane?

Upward into the extraperitoneal pelvis around the bladder, not into the perineum.

Why is erectile dysfunction common after pelvic-fracture injury of the membranous urethra?

The cavernous nerves and arteries pass right beside the membranous urethra.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): pars intermedia urethrae masculinae
Official Spanish (DeCS): Porción intermedia (membranosa) de la uretra masculina
English (TA2): Intermediate part of male urethra

Sources: Anatomy, Abdomen and Pelvis, Male Genitourinary Tract; Anatomy, Abdomen and Pelvis, Sphincter Urethrae; Anatomy of the Human Body (20th ed.): Surface Markings of the Perineum (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain; 25.2 Gross Anatomy of Urine Transport (OpenStax (Rice University), 2022) · adapted, CC BY 4.0.

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Representative model, for educational purposes only.