Cadaveric study of nerves supplying the membranous urethra

To better understand the anatomy of the region of the male membranous urethra in order to preserve continence during radical cystectomy and prostatectomy.

Cadaveric dissections of 15 male specimens were undertaken to investigate the nerves to membranous urethra. The nerves were traced from both an intrapelvic approach and a perineal approach. The origin, course, and distribution of the branches to the membranous urethra region were investigated in detail.

The membranous urethra is innervated by branches of inferior hypogastric plexus (IHP) and intrapelvic and extrapelvic branches of pudendal nerve (PN). The pelvic nerve from IHP originated from the caudal most root of the pelvic splanchnic nerve, running along the surface of the levator ani muscle (LAM) to enter the membranous urethra at the 5 and 7 O'clock positions. In 40% of specimens we found that the intrapelvic branches were supplied by the PN. Before exiting the pudendal canal, PN gives off an intrapelvic branch that traverses the LAM to course with the pelvic nerve and innervate the membranous urethra; the distance between these intrapelvic branches and prostatic apex is 5.3 +/- 1.8 mm. The branches originating from the dorsal nerve of penis innervate the membranous urethra in 53.3% of specimens; these nerve branches are located 4.2 +/- 1.1 mm from the prostatic apex.

Dissection of the seminal vesicles and the prostatic apex during radical cystectomy and prostatectomy likely injures the nerve responsible for continence.