document: radical retropubic prostatectomy is the surgical treatment of choice for patients with localized prostate cancer . 
   numerous studies have been published demonstrating excellent tumor control , good functional results , and low morbidity associated with the procedure ( 1 - 4 ) . 
   however , the major long - term morbidity from radical retropubic prostatectomy that remains is erectile dysfunction , despite advances in surgical techniques . 
   prior to studies done by walsh and donker ( 5 ) using male fetuses , the cause of erectile dysfunction after radical prostatectomy was not well understood . 
   they proposed and eventually demonstrated that erectile dysfunction occurred secondary to the injury of cavernosal nerves . 
   these nerves were identified branching from the pelvic plexus and running as a plexus of small nerves within a prominent neurovascular bundle on the posterolateral border of the prostate , terminating in the region of the membranous urethra . 
   these nerves are mainly concentrated laterally to the prostate and these neural structures are referred to as neurovascular bundles . 
   nerve sparing radical retropubic prostatectomy has led to improvements in potency rates , with studies reporting a 16 to 76% recovery of erectile function in men whose bilateral neurovascular bundles were preserved and 0 to 56% in those with unilateral neurovascular bundle preservation ( 6 , 7 ) . 
   this variability can be attributed to the fact that there was no definite and exact anatomy of periprostatic nerve fibers , especially the cavernosal nerves . 
   although some papers about the anatomy of periprostatic nerves were published recently , there are still controversies about detailed descriptions of the exact periprostatic nerve distribution in the literature . 
   thus , in the present study , we described periprostatic nerve distribution and constructed a 3-dimensional model of nerve distribution . 
   the prostate , together with seminal vesicle , bladder , and rectum , was removed en bloc from five adult male human cadavers ( age at death 43 - 72 yr ) after filling urinary bladder with 40% formaldehyde using urethral catheter . 
   each specimen was sliced by 5 mm step sections from the base of the prostate to the apex , and a total of eight slices of whole - mount histologic sections were embedded in paraffin , and prepared , and then stained with anti - s-100 antibody neural stain to delineate the precise location of this neural tissue . 
   immunostaining with anti - s-100 protein antibody was performed by dewaxing the slides in xylene three times for three minutes and then rehydrating in ethanol ( two changes of three minutes in 100% ethanol and two changes of three minutes in 90% ethanol ) and distilled water . 
   the rabbit polyclonal primary antibody to s-100 protein ( immunon , pittsburgh , pa , usa ) was applied in a 1:500 dilution and incubated for one hour at room temperature . 
   the samples were then washed in pbs , subjected to envision - hrp kit ( dako , carpinteria , ca , usa ) , and the reaction product was visualized with chromogen 3 , 3'-diaminobenzidine ( dab ) for three minutes . 
   the stained whole - mount section slide was divided into four arbitrary sectors : two laterals , one ventral , and one dorsal ( rectal side ) according to one fourth the circumference of whole - mount specimens . 
   whole - mount specimens were then divided by two axes , such as from 1.5 to 7.5 o'clock and 10.5 to 4.5 o'clock direction ( fig . 
   each slide was taken from the base , mid - part , and apex of the prostate . 
   nerve fibers 100 micrometer or greater in diameter were counted in 200 magnification microscopically ( olympus bx51 ; tokyo , japan ) , in addition to the number of nerve fibers , the distance from nerve fiber to the true prostate capsule , and nerve fiber diameter on each sector from representative slides . 
   the three - dimensional periprostatic nerve distribution model was made by connecting the stained nerve fibers from the same location of the same sectors of the eight whole - mount slides from each prostate and reconstructing its image after taking a picture of the three - dimensional model ( fig . 
   the difference in variables was assessed using anova and kruskal - wallis nonparametric anova . statistical significance in this study was considered at p<0.05 . 
   the average number of nerve fibers located in the ventral part of the prostate was 5.751.20 , and comparatively , the average number in the dorsal ( rectal ) part was 28.502.17 . 
   there were even fewer nerve fibers in the ventral part of the prostatic base area , numbering 3.751.38 . 
   in the right lateral part the average number of nerve fibers was 25.259.92 , and in the left lateral part 25.7512.76 ; thus the number of nerve fibers in the dorsal ( rectal ) , right lateral , and left lateral parts of the prostate capsule showed no significant difference , and nerve fibers were distributed evenly around the prostatic capsule microscopically in the posterior , right lateral , and those in left lateral areas . 
   however , nerve fibers in the ventral part were small in number compared to the dorsal , right lateral , and left lateral parts at all levels ( p=0.001 ) ( table 1 ) . moving from base to apex , the average number of nerve fibers increased in the ventral area , but this increase was not statistically significant ( p=0.386 ) . 
   the average distance from prostatic capsule to nerve fibers was 1.730.43 mm in the ventral part , 1.800.16 mm in the dorsal ( rectal ) part , 1.580.26 mm in the right lateral part , and 1.230.29 mm in the left lateral part . 
   there was no difference in the average distances when comparing the four different parts statistically ( p=0.266 ) . 
   also there was no significant difference among the base , mid - part , and apex levels ( p=0.673 ) ( table 2 ) . 
   the average thicknesses of nerve fibers in the ventral and dorsal parts were 0.190.02 mm and 0.300.03 mm , and those in the right and left lateral parts were 0.300.03 mm and 0.280.03 mm , respectively . 
   there was no difference in nerve fiber thickness according to level such as base , midpart , and apex ( p=0.180 ) . 
   however , the average thickness of the nerve fibers in the ventral part was significantly decreased as compared to the other parts ( p=0.005 ) ( table 3 ) . the three - dimensional model of the periprostatic nerve fibers revealed an almost even distribution and nearly similar thickness of periprostatic nerve fibers on dorsal and both lateral parts . 
   furthermore , there was absence of a cord - like structure , such as neurovascular bundle , noted on the study . however , the nerve fibers in the ventral part were substantially fewer in number and decreased in thickness . 
   traditionally , it was thought that cavernosal nerves branched from the pelvic plexus and ran as a plexus of small nerves within a prominent cord - like neurovascular bundle on the posterolateral border of the prostate ( 5 , 8) . 
   new advancements in surgery , including the use of laparoscopic and robotic modalities and magnifying visual devices in open surgery , have enabled precise nerve dissection . however , despite all these advancements in nerve preservation or restoration , potency rates have remained unsatisfactory ( 9 - 11 ) . 
   recently , several descriptions of the neurovascular bundle have been proposed : the neurovascular bundle , in contrast to the usual concept , appears to contain few pelvic splanchnic nerve components at the bladder - prostate junction . 
   the pelvic splanchnic nerve branches demonstrate a spray - like distribution , and caudal branches reach the dorsolateral portion of the prostate at levels more than 20 mm inferior to the bladder - prostate junction . 
   therefore , the cavernous nerves appear to be spread and located beyond the neurovascular bundle ( 12 ) . 
   ( 13 ) found , in addition to the main neurovascular bundles , other nerve branches running between the prostatic capsule and endopelvic fascia , and called them distal accessory nerve pathway . 
   according to these authors , this pathway could explain the unpredictable response to erection recovery and the lack of correlation between surgeon perception of the quality of neurovascular sparing and functional results after radical prostatectomy . 
   recently , several descriptions of the neurovascular bundle have shown variations in the distributions of autonomic fibers between different individuals . 
   about half of the patients have been reported as having a ' fan - like ' nerve fiber distribution on the lateral aspect of the prostate ( 14 ) . as mentioned above , the traditional knowledge of the neurovascular bundle has been challenged . 
   therefore , we performed this study to distinguish microscopic features and anatomic navigation of periprostatic nerves using male adult cadavers . 
   we found that the number of periprostatic nerve fibers was distributed evenly to dorsal and both lateral area of the prostate in our study . unlike the study of kiyoshima et al . 
   ( 14 ) , no cord - like neurovascular bundle was observed in any cadaver case in our study . 
   in addition , the distances from the prostatic capsule were almost the same in both the lateral and dorsal ( rectal ) parts of the base , middle , and apex levels of the prostate . 
   these data , including numerical values about periprostatic nerve fibers , have not been reported and will serve as a guide for improved results for nerve sparing radical prostatectomy . 
   several urologists reported surgical techniques according to the anatomy of the neurovascular bundle related to postoperative sexual dysfunction ( 14 , 15 ) . 
   ( 16 ) suggested a modified technique of nerve sparing called " curtain dissection " , which involves incising the periprostatic fascia and dissecting the neurovascular bundle far more anteriorly than previously described . 
   ( 2 ) reported the technique of open retropubic nerve - sparing radical prostatectomy . in their study , the parapelvic fascia of the prostate is incised at the lateroventral aspect of the prostate at 10 o'clock and 2 o'clock . 
   they noted the importance of starting the incision high up on the ventral aspect of the prostate to preserve a maximum number of nerve fibers because a substantial number of nerve fibers are located at the ventral area . 
   it has been shown that potency rates strongly correlate with the number of preserved nerve fibers . 
   had introduced their modified technique of robotic radical prostatectomy , named vattikuti institute prostatectomy ( 17 ) . 
   the features of their technique are early transaction of the bladder neck , preservation of the prostatic fascia ( veil of aphrodite ) , and control of the dorsal vein complex after dissection of the prostatic apex . 
   they reported that the veil nerve sparing procedure offers superior erectile function compared with conventional nerve - sparing surgery without compromising cancer control ( 18 ) . 
   ( 19 ) performed a histologic study of comparison between the veil of aphrodite technique and standard nerve - sparing technique during a robotic prostatectomy . 
   they concluded that the veil of aphrodite technique is a safe procedure that effectively preserved the lateral prostatic fascia , which contains nerve bundles that run along the surface of the anterolateral zones . in their study , the nerve bundle counts of the anterolateral zones was different between the two techniques with statistical significance . 
   our result means modified nerve - sparing techniques by incising the periprostatic fascia more anteriorly are feasible for saving periprostatic nerves . 
   but an excessive high up incision ( over 2 , 10 o'clock ) would not be effective because the number of nerve fibers of both lateral parts is much more than that of the ventral part of the periprostatic area . 
   these findings are differernt from eichelberg 's reports that the sum of the median percentage of nerves detected in anterior half of the prostate was more than 20% ( 20 ) . 
   our result revealed that the mean percentage of nerves in ventral part was 6.7% ( range : 4.5 - 9.4% ) ( table 1 ) . according to costello et al . 
   ( 21 ) , the majority of nerves which exist on the anterior aspect of the prostate laterally are not functionally significant parasympathetic nerves . 
   so , there is little evidence to support higher incisions in the lateral prostatic fascia anatomically . based on this study , 
   the number of periprostatic nerve fibers is evenly distributed on both lateral and dorsal ( rectal ) parts from base to apex of the prostate without forming any cord - like structures . because the number of nerve fibers on the ventral part is few in comparison , an excessive high up incision over 2 , 10 o'clock on the ventral part of the prostate is insignificant during nerve - sparing radical prostatectomy .
summary: we investigated the distribution and navigation of periprostatic nerve fibers and constructed a 3-dimensional model of nerve distribution . 
   a total of 5 cadaver specimens were serially sectioned in a transverse direction with 0.5 cm intervals . 
   hematoxylineosin staining and immunohistochemical staining were then performed on whole - mount sections . 
   three representative slides from the base , mid - part , and apex of each prostate were subsequently divided into 4 sectors : two lateral , one ventral , and one dorsal ( rectal ) part . 
   the number of nerve fibers , the distance from nerve fiber to prostate capsule , and the nerve fiber diameters were analyzed on each sector from the representative slides by microscopy . 
   periprostatic nerve fibers revealed a relatively even distribution in both lateral and dorsal parts of the prostate . 
   there was no difference in the distances from the prostate capsule to nerve fibers . 
   nerve fibers in the ventral area were also thinner as compared to other areas . in conclusion , 
   periprostatic nerve fibers were observed to be distributed evenly in the periprostatic area , with the exception of the ventral area . as the number of nerve fibers on the ventral part is fewer in comparison , 
   an excessive high up incision is insignificant during the nerve - sparing radical prostatectomy .