Sunday, May 23, 2010

Male Urethra

The male urethra is divided into posterior and anterior parts, separated by the urogenital diaphragm. The posterior urethra is divided into prostatic and membranous portions, while the anterior urethra is divided into bulbous and penile segments.

Posterior Urethra



Prostatic Urethra

The prostatic urethra contains an elevation along its posterior wall called the verumontanum (mountain ridge).

Müllerian duct cysts, cystic lesions that are derived from the caudal ends of fused Müllerian ducts, can originate at the level of the verumontanum and extend posteromedially. Müllerian duct cysts are usually isolated abnormalities (rarely associated with renal agenesis) and usually present in the 3rd and 4th decades of life. They do not communicate with the urethra, but are connected to the verumontanum by a thin stalk. These findings are in contrast to another midline cyst arising from the verumontanum, the prostatic utricle cyst (see below), which is seen in children in association with other abnormalities and communicates with the prostatic urethra. Mnemonic: Müllerian duct cysts in Men.

The prostatic utricle is an indentation at the inferior verumontanum and is a remnant of the Müllerian duct system. On each side of the prostatic utricle are the ejaculatory ducts.

A prostatic utricle cyst, which may mimic a Müllerian duct cyst (see above), presents as a cyst along the midline posterior margin of the prostate. It is seen in children in association with hypospadias or incomplete testicular descent. The prostatic utricle cyst communicates with the prostatic urethra.

On each side of the verumontanum are openings for the ducts of the prostate.

Membranous Urethra

The membranous urethra is the shortest, narrowest, and least distensible part of the male urethra and is surrounded by the external urethral sphincter (EUS in image). The membranous urethra is susceptible to iatrogenic stricture formation. The membranous urethra is the most common site of stricture formation following transurethral resection of the prostate. The Cowper (bulbourethral) glands live posterolateral to the membranous urethra. Cowper glands are developmentally similar to Bartholin glands in women. Like Bartholin glands, the Cowper glands secrete lubricant.

Anterior Urethra

Iatrogenic strictures may be found at the penoscrotal junction of the anterior urethra. Multiple openings for the glands of Littré can be found throughout. In cases of stricture proximally, the ducts for the glands of Littré expand and can fill with contrast on retrograde urethrogram.

Bulbar Urethra

The bulbar urethra is the widest part of the urethra. The ducts of the Cowper glands empty here. Post-gonococcal strictures are typically located in the proximal bulbar urethra. In such cases, there may be backflow of contrast into the ducts of the Cowper glands on retrograde urethrography. Strictures may occur here following TURP due to current leakage from insufficient lubricant isolation.

Penile Urethra

The distal portion of the penile urethra opens up into the fossa navicularis. Strictures can occur at the meatus following TURP due to inappropriate sizing of the instrument in relation to the diameter of the urethral meatus.

References

  • Balbay MD, et al. Development of urethral stricture after transurethral prostatectomy: a retrospective study. Int Urol Nephrol. 1992;24(1):49-53.
  • Donkol RH, Monib S, Moghazy K. Müllerian duct cyst as a cause of acute infantile-onset epididymitis. Pediatr Radiol. 2006 Nov;36(11):1197-9.
  • Rassweiler J, Teber D, Kuntz R, Hofmann R. Complications of transurethral resection of the prostate (TURP)--incidence, management, and prevention. Eur Urol. 2006 Nov;50(5):969-79.
  • Thurnher S, Hricak H, Tanagho EA. Müllerian duct cyst: diagnosis with MR imaging. Radiology. 1988 Jul;168(1):25-8.
  • Zagoria RJ and Tung GA (1997). Chapter 6. in Genitourinary Radiology: The Requisites.

No comments:

Post a Comment