Anatomical considerations of selective pudendal neurectomy

Somatic innervation of the feline lower urinary tract

Electrical stimulation of pudendal nerve sensory pathways can evoke excitatory bladder reflexes. However, the precise peripheral innervation pattern of these somatic fibers remains unclear. In adult male cats, we investigated pudendal nerve innervation of the lower urinary tract (LUT) by employing anatomical (Sihler's stain) and electrophysiological (selective electrical nerve stimulation) techniques. The stained specimens revealed differential innervation of the proximal and distal urethrae by fibers derived from the sensory branch of the pudendal nerve. Cranial sensory branch fibers penetrated the prostate to terminate along the intraluminal surface of the urethra, whereas the dorsal nerve of the penis primarily innervated the glans penis. Further examination of the proximal urethra showed a separate pathway (deep perineal nerve) that inserted directly into the external urethral sphincter. These observations were confirmed electrophysiologically by the measured urethral sphincter activity evoked in response to selective nerve stimulation. Electrical activation of the sensory pathway evoked only reflex (latency=8.9+/-1.1 ms) contractions of the urethral muscle, whereas stimulation of the perineal pathway elicited direct (latency=1.3+/-0.1 ms) responses. Our findings identify specific pudendal nerve sensory pathways that can be used potentially to restore bladder function in persons with spinal cord injury and also treat LUT symptoms such as urinary retention.

The course and branching pattern of pudendal nerve in fetus

The pudendal nerve is a considerably large branch of the sacral plexus. There are many articles in the literature concerning the pudendal nerve in adults, but as far as we know, there is none on the branching pattern and variations in pudendal nerve anatomy in fetus. This study investigates the pudendal nerve trunking with respect to the piriformis muscle in 25 formalin-fixed fetuses (50 sides of pelves, 15 females, 10 males), ranging from 20 to 37 weeks of gestation. We investigate pudendal nerve trunking in four types: Type I-a is defined as single-trunk with the inferior rectal nerve branching proximal to the dorsal nerve of penis/clitoris (38%), Type I-b is also single-trunk with the dorsal nerve of penis/clitoris branching proximal to the inferior rectal nerve (24%), Type II is double-trunk with medial trunk as an inferior rectal nerve (34%), and Type III is triple-trunk (4%). We measured the average diameter of the main trunk of pudendal nerve in Type I-a and I-b groups to be 0.98 +/- 0.33 mm. We also measured the average length of the pudendal nerve trunks before the dorsal nerve of penis/clitoris branch to be 7.35 +/- 3.50 mm. There was no significant statistical difference in the average length, diameter, number of trunks, and pudendal nerve variations between male and female and also right and left sides of the pelves. This first and detailed fetal study of pudendal nerve trunking with respect to the piriformis muscle would be useful for educational anatomy dissections and anatomical landmark definitions for relevant clinical procedures.

Pudendal nerve stimulation evokes reflex bladder contractions in persons with chronic spinal cord injury

AIMS

Although electrical stimulation of the pudendal nerve has been shown to evoke reflex micturition-like bladder contractions in both intact and spinalized cats, there is little evidence to suggest that an analogous excitatory reflex exists in humans, particularly those with spinal cord injury (SCI). We present two cases where electrical activation of pudendal nerve afferents was used to evoke excitatory bladder responses.

SUBJECTS AND METHODS

A percutaneously placed catheter electrode was used to electrically stimulate the pudendal nerve trunk in two males with SCI. The response was quantified with recorded changes in detrusor pressure and EMG activity of the external anal sphincter.

RESULTS

In both individuals, frequency specific (f = 20-50 Hz) activation of the pudendal nerve trunk evoked excitatory bladder contractions that also depended on the stimulus amplitude and bladder volume.

CONCLUSION

The results suggest that selective activation of the perineal branches of the pudendal nerve may further augment the excitatory reflex evoked by electrical stimulation.

Fascicular anatomy and surgical access of the human pudendal nerve

The ability to access selectively distal nerve branches at the level of the compound pudendal nerve (PN) would allow control of multiple neural pathways and genitourinary functions at a single location. Nerve cuff electrodes can selectively stimulate individual fascicles; however the PN fascicular anatomy is unknown. The fascicular representation of distal branches was identified and traced proximally to create fascicle maps of 12 compound PNs in seven cadavers. Distal nerves were represented as groups of individual fascicles in the PN. Fascicle maps were consistent between specimens and along the PN within specimens. PN branch free length was 26+/-7.7 mm. PN cross-sections were relatively flat with major and minor diameters of 4.3+/-0.90 and 1.7+/-0.45 mm, respectively. Placing a nerve cuff on the PN is anatomically and surgically feasible. The PN fascicular anatomy, branch free length, and cross-section geometry are conducive to selective stimulation of distal nerves with a single nerve cuff electrode.

Anatomical study of the pudendal nerve adjacent to the sacrospinous ligament

The pudendal nerve (S3-S5) is a major branch of the sacral plexus. After branching from the sacral plexus, the pudendal nerve travels through three main regions: the gluteal region, the pudendal canal, and the perineum. In the gluteal region, the pudendal nerve lies posterior to the sacrospinous ligament. The relationship of the pudendal nerve to the sacrospinous ligament has important clinical ramifications, but there is a lack of literature examining the variations in pudendal nerve anatomy in the gluteal region. This study investigates the pudendal nerve trunking in relation to the sacrospinous ligament in 37 cadavers (73 sides of pelves) of 21 males and 16 females, ranging from 18-83 years of age. Pudendal nerve trunking could be grouped into five types: Type I is defined as one-trunked (41/73; 56.2%), Type II is two-trunked (8/73; 11%), Type III is two-trunked with one trunk as an inferior rectal nerve piercing through the sacrospinous ligament (8/73; 11%), Type IV is two-trunked with one as an inferior rectal nerve not piercing through the sacrospinous ligament (7/73; 9.5%), and Type V is three-trunked (9/73; 12.3%). In summary, 56.2% of pudendal nerves adjacent to the sacrospinous ligament were one-trunked, 31.5% were two-trunked and 12.3% were three-trunked. Fifteen inferior rectal nerves originated independently from the S4 root and never joined the main pudendal nerve. Eight of fifteen inferior rectal nerves pierced through the sacrospinous ligament, perhaps making it prone for entrapment. We measured the average diameter of the main trunk of the pudendal nerve to be 4.67 +/- 1.17 mm. We also measured the average length of the pudendal nerve trunks before terminal branching to be 25.14 +/- 10.29 mm. There was no significant statistical difference in the average length, average diameter, number of trunks, and pudendal nerve variations between male and female or right or left sides of the pelves. A detailed study of pudendal nerve trunking in relationship to the sacrospinous ligament would be useful for instruction in basic anatomy courses and in relevant clinical settings as well.

New, simple, ultrasound-guided infiltration of the pudendal nerve: ultrasonographic technique

PURPOSE

Anesthetic infiltration of the pudendal nerve at the ischial spine can relieve perineal pain in cases of compression or distention. The aim of our study was to look for a real-time, visually controlled infiltration technique using ultrasound.

METHODS

Fifty-three volunteers were examined in a prone position using a 3.5-MHz curved-array probe in color-coded Doppler mode. The deep gluteal region was scanned in two perpendicular planes, longitudinal and transverse to the internal pudendal artery.

RESULTS

On the transverse planes the ischial spine, the sacrospinous ligament, and the internal pudendal artery were depicted in all but two cases. In 47.2 percent of the cases one trunk of the pudendal nerve was detected directly. Nerves consisting of more than one trunk were not found. The thickness of the nerve ranged between 3.5 and 7 mm.

CONCLUSIONS

In almost one-half of the cases a direct ultrasound-guided infiltration of the pudendal nerve is possible. In the remaining cases the nerve can be detected and blocked indirectly, using the ischial spine or the internal pudendal artery as a landmark.

New, simple, ultrasound-guided infiltration of the pudendal nerve: topographic basics

PURPOSE

We report the topographic relationship of the pudendal nerve to the accompanying pudendal vessels and the ischial spine and provide the basics for an ultrasonographic depiction of these structures.

METHODS

Twenty-nine female and 29 male adult human cadavers were positioned prone to expose the deep gluteal region. In 58 left and 58 right pelves the course of the pudendal nerve and vessels at the ischial spine were evaluated and analyzed statistically (n = 116).

RESULTS

Multitrunked pudendal nerves were found in 40.5 percent with a left-vs.-right ratio of 1:1.5. The diameters of the single-trunked nerves ranged from 1.3 to 6.8 (mean 3.6 +/- 1.1) mm. In 75.9 percent the pudendal nerve was found medial to the accompanying internal pudendal artery. The distance to the artery ranged from 17.2 mm medial to 8 mm lateral (mean, 3.4 mm medial +/- 4.1 mm). The distance to the tip of the ischial spine ranged from 13.4 mm medial to 7.4 mm lateral (mean, 2.1 mm medial +/- 3.7 mm).

CONCLUSIONS

The knowledge of the close spatial relationship between the pudendal nerve and the internal pudendal artery is important for any infiltration technique and even surgical release. It demands real-time, visually controlled infiltration techniques, such as with ultrasound.

Experimental model of anorectal transplantation

BACKGROUND

Anorectal transplantation with pudendal nerve anastomosis after rectal excision is a possible strategy that would avoid a colostomy and recreate potentially normal anorectal function. This study investigates the technical feasibility of anorectal transplantation with pudendal nerve and inferior mesenteric artery and vein anastomosis in a porcine model.

METHODS

Four female pigs (22-42 kg) provided donor anorectum for four male recipients (29-39 kg) under standard general anaesthesia. The donor operation involved abdominoperineal excision of rectum (APR) taking the anal sphincter, pudendal neurovascular bundle and inferior mesenteric vessels. The recipient underwent APR, transperineal introduction of the donor graft, anastomoses of the rectum, inferior mesenteric vessels and pudendal neurovascular bundle, and perineal closure. Recorded variables were duration of each step of transplantation, ischaemic time, dimensions of anastomosed structures and postoperative graft viability. Animals were killed at 24 h, the state of the graft was noted and tissue was taken for confirmatory histology.

RESULTS

Mean operation time was 372 (range 303-435)min. Mean ischaemic time was 118 (100-130)min. Before death, observation at laparotomy revealed two pink grafts, one slightly dusky but healthy graft and one outright failure, reflecting the state of the mesenteric vessels, which were patent in three and thrombosed in one. Histological examination showed no difference between control biopsies and the three cases with satisfactory mesenteric flow. Gross ischaemia was present histologically in the failed case.

CONCLUSION

Anorectal transplantation is technically feasible in a pig model. Longer-term studies are now needed to assess return of function and overcome rejection issues.

New, simple approach for maximal pudendal nerve exposure: anomalies and prospects for functional reconstruction

PURPOSE

Functional neosphincters after pudendal nerve anastomosis proved possible in animal models and may be applicable in humans, but access is a recognized problem. We report the occurrence of pudendal nerve anomalies, its implications for reconstruction, and describe a new approach for maximal exposure.

METHODS

Adult human cadavers were positioned prone and dissected via a gluteal approach. Pudendal nerve variations and physical measurements were analyzed statistically.

RESULTS

A new, simple, four-step approach (surface landmarks and exposure of gluteus maximus muscle, sacrotuberous ligament, and pudendal neurovascular bundle) permitted optimal pudendal nerve exposure in all 14 human cadavers (28 limbs). Six were males and had a mean age of 82 (range, 58-102) years. Two anomalies, Type 1 (2-trunked) and Type 2 (3-trunked), of the pudendal nerve were recognized in 30 percent of cadavers, with a left-to-right ratio of 2.5:1. Mean pudendal nerve length over the ischial spine was 23.9 (range, 19-28) mm right, 24.2 (range, 19-28) mm left (P = 0.54), but its diameter measured 5.2 mm (right) and 4.9 mm (left; P = 0.04). Mean length of pudendal nerve trunk exposed after reflection of the sacrotuberous ligament was 55 (range, 44-75) mm on either side before division into terminal branches. The number and percent frequency of inferior rectal nerve on both sides were 1 (13 percent), 2 (76 percent), and 3 (11 percent), respectively, with a mean length of 27.1 (range, 21-34) mm right and 27.9 (range, 20-33) mm left (P = 0.31).

CONCLUSION

A simple four-step approach to the pudendal nerve contributes to improved access in all cases. It facilitates reconstruction because it allows accurate nerve selection and recognition of potential anomalies that might influence functional outcome.

Neuroanatomy of the striated muscular anal continence mechanism. Implications for the use of neurostimulation

The striated pelvic floor musculature and the striated muscle of the external and sphincter contribute to anal continence by effecting, respectively, the rectoanal angulation of the bowel and an anal high pressure zone. The muscular anatomy of the pelvic floor is generally understood, but the neuroanatomy remains controversial. The authors dissected three male cadavers and traced the sacral nerves from their entrance into the pelvis through the sacral foramina throughout their branching to their final destinations. Deriving from a common source, the sacral nerves S2 to S4, the neural supply of the levator ani was distinct from that of the external anal sphincter: the levator is supplied by direct branches splitting from the sacral nerves proximal to the sacral plexus and running on the inner surface; the external anal sphincter is supplied by nerve fibres travelling with the pudendal nerve on the levator's undersurface. To document the functional relevance of these anatomic findings, stimulation of the pudendal and sacral nerves was performed at different levels in five patients with lower urinary tract dysfunction. Stimulation of the pudendal nerve increased the anal pressure, whereas stimulation of S3 increased it only slightly but caused an impressive decrease of the rectoanal angle; when S3 was stimulated after bilateral pudendal block, anal pressure did not change but the decrease in the rectoanal angulation persisted. The changes in anal pressure could be obtained without fatigue at stimulation frequencies of 10 to 20 Hz.