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Introduction
Pudendal nerve arises from the anterior division of S2, S3, and S4. The anatomy of the pudendal nerve is hidden and complicated, which involves a meticulous time-consuming dissection to see the whole course of the pudendal nerve. It is the prime source of innervation for the pelvic muscles and maintains the integrity of the bladder and the bowel [1]. Pudendal nerve entrapment clinically has a wide spectrum of presentation ranging from urinary to anorectal and sexual dysfunction [2]. Any inadvertent injury to this nerve greatly affects the quality of life. Though conservative management is used as the first line of treatment, surgical interventions like transperineal, or gluteal, or ischiorectal approaches are also widely used and laparoscopic interventions are considered the gold standard [2].
Although very few studies were conducted earlier on the pudendal nerve, there is a paucity in the literature regarding the complete course of the pudendal nerve and studies suggesting the cross-sectional area (CSA) of the pudendal nerve at various site of entrapment is also missing especially in Indian population. Thus, the present study aimed at providing the CSA of the pudendal nerve at various site of entrapment and trajectory distances from possible anatomical landmarks that can be used to locate the pudendal nerve surgically.
Materials and Methods
The present study was a descriptive study done in the Department of Anatomy, All India Institute of Medical Sciences (AIIMS) Kalyani, over a period of 2 months. Around 10 cadaveric specimens with equal sex distribution (5 male and 5 female) were taken for dissection. The cadaveric specimens without any gross abnormality were included and the specimens with distorted pelvis anatomy, broken pelvis were excluded from the study. The study was started after the approval of Institute Ethics Committee (IEC) AIIMS, Kalyani (IEC/AIIMS/Kalyani/certificate/2024/436).
The pelvic organs were removed, and the sacral plexus was identified after removing the pelvic fascia. The plexus was traced from the level of roots to the branches and the variations in the formation of the pudendal nerve were noted. The pudendal nerve was identified at the gluteal region below the piriformis muscle and was traced further into the ischioanal fossa. The branches of the nerve were dissected in the ischioanal fossa and the morphometric measurements were taken. Further the dissection was carried out over the external genital organ to find the dorsal nerve of penis/clitoris and the measurements were taken. All the measurements were done by using digital vernier calliper.
Transverse diameter (TD) and longitudinal diameter (LD) of the pudendal nerve at various sites of entrapment like piriformis, at sacrospinous ligament, at sacrotuberous ligament, and at Alcock’s canal were taken. The CSA is calculated using the formula TD×LD×π(3.14159)/4.
Trajectory distances for the pudendal nerve from various anatomical sites like ischial spine, upper end of ischial tuberosity and distance from anal sphincter to inferior rectal nerve was measured. Distance from inferior border of pubic symphysis to dorsal nerve of penis/clitoris and from mid-point of inferior pubic ramus to dorsal nerve of penis/clitoris was also measured. The schematic representation showing the trajectory measurements from various anatomical landmarks is given in Fig. 1.
All the measurements were taken thrice, and its mean was taken as final. Measurements from around 3 specimens were repeated after a month by the principal investigator to overcome intraobserver variability and the measurements were taken again by another investigator after a month to overcome interobserver variability.
Statistical analysis
The quantitative data was expressed as mean standard deviation or median interquartile range. Normality check was done using Shapiro–Wilk test. For comparison between sex and sides for normally distributed data independent Student’s t-test and for non-normally distributed data Mann–Whitney test was used. All statistical analysis were carried out at 95% confidence interval and a P-value of less than 0.05 will be taken as significant. IBM SPSS Statistics for Windows Version 19.0 (IBM Co.) was used for statistical analysis.
Results
Morphological variations
In a male cadaver the pudendal nerve was originating from S3-S4 roots on both right and left side. There was communication of pudendal nerve with sciatic nerve in 9 cadavers bilaterally. Whereas, the variation in trunking of pudendal nerve was found in 4 cadavers bilaterally. In 6 cadaveric specimen we found 1 trunk (60%), in 2 (1 male and 1 female) cadaveric specimens we found two trunked pudendal nerve bilaterally (20%), in 1 male cadaver we found 3 trunks of pudendal nerve (10%), and in 1 male cadaver 4 trunks of pudendal nerve were present bilaterally. The formation and trunking variations in pudendal nerve is given in Fig. 2.
Morphometry
The maximum CSA was found below the piriformis (4.04 mm2). The CSA reduced as the nerve travelled further into the Alcock’s canal (0.35 mm2). Irrespective of sites all the CSA were larger among the males. The CSA values were larger on the right side except at the sacrotuberous ligament. The cadaveric image showing the CSA measurements at piriformis and at sacrospinous ligament are given in Fig. 3. All the trajectory distances were larger on the right side except distance from ischial tuberosity to pudendal nerve and from midpoint of inferior pubic ramus to dorsal nerve of penis/clitoris. The distance between ischial spine to pudendal nerve and from inferior border of pubic symphysis to dorsal nerve of penis/clitoris were larger among females. The cadaveric images showing the trajectory measurements from ischial spine to pudendal nerve and from anal sphincter to inferior rectal nerve and distance to dorsal nerve of penis/clitoris from inferior border of pubic symphysis are given in Fig. 4. On comparison with sex and sides there was no statistically significant difference neither for CSA of pudendal nerve nor for the trajectory distances to the pudendal nerve. The comparison of CSA and trajectory distances between sides are given in Figs. 5, 6 respectively. The comparison of CSA and trajectory distances between sex are given in Tables 1 and 2 respectively.
Discussion
Morphological variations
In our study there was communication of pudendal nerve with sciatic nerve in 9 cadavers bilaterally. Connection with the sciatic nerve was observed in 14 out of 52 hemipelves (26.9%) [3]. There is no research article or case report that clearly explains the communication of pudendal nerve with sciatic nerve. This communication would lead to aberrant blockade of both the nerves when one of the nerves is blocked intentionally [3].
In the present study 4 cadavers (60%) had single trunk, 2 cadavers (20%) had two trunks, and three and four trunks were present in 1 cadaver (10% each). Gruber et al. [4] found multiple trunks in 40.5% and Maldonado et al. [5] found multiple trunks in 38%. Though in both the studies the number of trunks seen was not specified. Ranjan et al. [3] found, a single pudendal nerve trunk (type I) in 51.9% of hemipelves, two trunked pudendal nerves in 36.1% of hemipelves. Pudendal nerve with three trunks (type III) were found in 11.5% of hemipelves [3]. In a cadaveric study by Mahakkanukrauh et al. [6] type I was reported to be 56.2%, 11% of type II and III, whereas the type IV and V were reported to be 9.5% and 12.3% respectively. As reported earlier by Pirro et al. [7] there was no difference in trunking present between sides. If present it was present bilaterally like in our study as well. But Gruber et al. [4] found such variations related to the trunking of the pudendal nerve between sides. However, the authors couldn’t explain the reasons behind these variations in trunking between sides [4].
Morphometry
As per the literature search there is a scarcity in the literature regarding the trajectory to pudendal nerve. The mean distance between ischial spine to pudendal nerve in our study was more among females (right, 5.86 mm; left, 5.64 mm) than males (right, 5.36 mm; left, 5.24 mm) and larger on the right side (5.61 mm) than left (5.44 mm). The mean values of distance in our study were larger compared to that obtained in the African and the European descent in a cadaveric study by van der Walt et al. [8]. In another cadaveric study by Sagsoz et al. [9] the distance measured was 2.98 mm in Turkey female population which was again lesser than that of our study. In our study the pudendal nerve was not directly related to the ischial spine in all the specimens, it was at some distance from the ischial spine. Shafik et al. [10] also found that the pudendal nerve was not crossing the ischial spine, which is consistent with our study. In contrast to this van der Walt et al. [8] have found the pudendal nerve lying exactly over the ischial spine.
In case of males in our study the mean values of distance from ischial spine to inferior rectal nerve were more or less equal to that of the males from African descent (8.58 mm), whereas the mean values in the Europeon descent was very less 1.94 mm [8]. The values obtained in the present study was larger among females than that of African (8.72 mm) and European (5.17 mm) descent [8]. These findings were not consistent with the present study. This might be due to the variations in the branching pattern of the inferior rectal nerve noted at various levels like proximal to Alcock’s canal, at Alcock’s canal or sometimes inferior rectal nerve directly coming from sacral plexus not branching from the pudendal nerve.
The mean distance between the anal sphincter to the inferior rectal nerve was larger among males (right, 20.04 mm; left, 20.30 mm) than females (right, 18.90 mm; left, 18.32 mm) and there were slightly larger in right (19.47 mm) than the left side (19.31 mm). When these values were compared to the maximum distance that was obtained from the anal skin to the inferior rectal nerve in the cadaveric study by van der Walt et al. [8], similar to our study the males of Europeon (24.25 mm) and the African (22.13 mm) descent had larger values than the females.
The distance from the inferior border of the pubic symphysis to the dorsal nerve of penis/clitoris were much larger than that of the African (male, 1.15 mm; female, 0.56 mm) and the Europeon descent (male, 1.55 mm; female, 0.15 mm) [8]. The distance from midpoint of inferior pubic ramus to the dorsal nerve of penis/clitoris was much larger in the males of the African descent (5.1 mm) compared to our study. This distance was lesser in females of both African (3.92 mm) and Europeon descent (3.79 mm) and males of the Europeon descent (4.22 mm) than our study [8]. This wide range of variation warrant us in establishing the population specific reference trajectory values to the pudendal nerve and its branches from various anatomical landmarks. Moreover this wide range of variations in measurements among various populations might be due to variations in the pelvic dimensions or body mass index in various population [8].
Cross-sectional area of pudendal nerve
The CSA of pudendal nerve at different landmarks were not extensively studied previously in the literature. In this study we have provided the CSA of the pudendal nerve at various possible anatomical landmarks. Previously in two cadaveric studies by Zhu et al. [11] and Barbe et al. [12] measured the pudendal nerve CSA at piriformis (7.02 mm2) and Alcock’s canal (5.64 mm2) respectively. The values obtained in both the studies were larger than our study.
Clinical/surgical implications
Picturising the multiple trunks is challenging both by direct depiction and by radiology. Nerves more than 4 mm could be imaged easily [4]. Neurolysis of one branch alone where there is actually more than one, might not have the desirable outcome and this fact might be the reason for the high failure rate of decompression surgeries through trans gluteal approach [13]. This would also be a hindrance in performing pudendal nerve anastomosis for sphincter reconstruction [7].
The distance of pudendal nerve from ischial spine is implicable in Richter’s stitch in transvaginal sacrospinous colpopexy and in pudendal nerve block [8]. It is safer to place the fixation stitch around 20 mm away from the ischial spine and more medially closer to the sacrum to prevent damage to the pudendal nerve [9]. Some other studies also propose placing a stitch at 1 or 2 fingers distance from ischial spine [14]. Placement of the stitch too lateral to the ligament or through its entire thickness leads to nerve entrapment [3]. But if the ischial spine is long then lateral placement of stitch can be considered [7]. Most of the pudendal nerve blocks are given at ischial spine in various obstetric procedures, in urology for prostate biopsies, in urethral reconstruction and to relieve bladder discomfort caused by catheter use [14, 15].
Damage to the terminal branches of the pudendal nerve might occur while operating the perianal fistula, during sphincter repair or damage in ischioanal fossa which might lead to faecal incontinence [8, 16]. In trans obturator tape outside in procedure for stress incontinence the trocar exits out near to the inferior pubic ramus where the dorsal nerve of penis/clitoris are vulnerable to injury. Similarly in the inside out trans obturator tape procedure the trocar exits out through the genitofemoral fold where the dorsal nerve of clitoris could be damaged in females. In males around 1 cm lateral territory around the bulb of the penis dissections should be avoided to preserve the deep perineal branches from injuries in trans obturator procedures [8]. Neurolysis of dorsal nerve of penis can be done at inferior pubic ramus relieves pain, restore ejaculatory and erectile function [17].
The CSA of pudendal nerve would be helpful in neurotization of the pudendal nerve. Neurotization of pudendal nerve is more successful than other nerve transfers since it is a distal nerve transfer, and the restoration of continence occurs in a very short span of time. Femoral nerve transfer is considered ideal because of its rich motor neurons and branching pattern. The calibre of the pudendal nerve is essential and it has to be matched with the calibre of the donor nerve for a successful nerve transfer [1]. The dimensions of the pudendal nerve also would be useful in successful implantation of the neuroprosthesis for urinary or faecal incontinence and the erectile dysfunction [10].
In our study we have presented the CSA of the pudendal nerve at multiple sites of entrapment. This would acts as the reference value for the East Indian population. These findings would help in surgeries of the perineum like fistula, hemorrhoids, draining of perianal abscess, and in various gynecological procedures like placement of vaginal clamps, surgeries of prolapse, and in nerve transfer in case of entrapment.
Since all of the specimens were of East Indian population, the generalizability of our findings may be constrained. Furthermore, the range of anatomic variability should be verified with larger anatomic studies because only 10 specimens were analyzed.
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