Male urethra

The male urethra is a fibromuscular tube that drains urine from the bladder. It has a longer, more complicated, course than the female urethra and is also more prone to pathology.

Gross anatomy

The male urethra measures, on average, 18-20 cm in length ⁶. It commences at the internal urethral orifice in the trigone of the bladder and opens in the navicular fossa of the glans penis at the external urethral meatus, which is the narrowest part of the urethra ⁵.

The male urethra can be divided into anterior and posterior portions. The anterior urethra is composed of the penile and bulbar urethra to the level of the urogenital diaphragm. The posterior urethra is composed of the membranous and prostatic urethra ⁵.

Anterior urethra

• penile (spongy, pendulous) urethra (~16 cm long): encased by corpus spongiosum of the penis

  • the longest portion

  • the fossa navicularis is a small normal dilatation of the distal penile urethra ⁵

• bulbar (bulbous) urethra: traverses the root of the penis

  • it receives the ducts from the bulbourethral glands and the glands of Littré

  • it has bulbous dilatation named intrabulbous fossa ⁵

The anterior urethra is lined by pseudostratified columnar epithelium. The very distal portion (at approximately the level of the fossa navicularis) is lined by squamous epithelium.

Posterior urethra

• membranous urethra (2 cm long): passes through the urogenital diaphragm, surrounded by external urethral sphincter ⁵

  • the shortest and narrowest portion ⁵

  • Cowper's gland surrounds the membraneous urethra ⁵

• prostatic urethra (3 cm long): surrounded by the prostate gland; on its posterior wall runs the urethral crest and the prominent smooth muscle verumontanum ⁵

  • the verumontanum receives the prostatic utricle in the midline and the ejaculatory ducts just distal to the prostatic utricle; on either side of it lie the prostatic sinuses, where numerous small prostatic ducts drain ⁵. The lower part of the prostatic urethra is fixed by puboprostatic ligament ⁵

The posterior urethra is lined by transitional columnar epithelium.

Arterial supply

• prostatic urethra: inferior vesical artery

• membranous urethra: bulbourethral artery

• penile urethra: branches of the internal pudendal artery

Venous drainage

• dorsal veins of the penis and internal pudendal vein that drain to the prostatic and vesical venous plexuses

• prostatic and vesical venous plexuses drain to internal iliac veins

Lymphatic drainage

• posterior urethra

  • internal iliac lymph nodes

  • external iliac lymph nodes

• anterior urethra

  • deep inguinal lymph nodes

  • superficial inguinal lymph nodes

Innervation

• prostatic plexus

Variant anatomy

• hypospadias

• epispadias

• posterior urethral valves

• urethral duplication

• congenital rectourethral fistulae

Radiographic features

Fluoroscopy

The division into anterior and posterior urethras is important in terms of pathology and in imaging the urethra: the anterior urethra being visualized by performing a retrograde (ascending) urethrogram and the posterior urethra with an antegrade (descending or micturating) urethrogram.

MRI

Urethral anatomy is best seen on T2WI ⁶:

• axial: membranous urethra is a low-intensity outer ring surrounding a high-intensity inner epithelium

• sagittal and coronal images may show the course of the anterior and posterior urethra but often the proximal prostatic and penile urethra are not well seen unless there is an indwelling Foley catheter

Related pathology

• urethral stricture

• urethral calculus

• urethral injury

• posterior urethral valve

• tumors of the male urethra

• urethral diverticulum

• hypospadia