This is formed from the anterior rami of S24 spinl nerves. It courses between the piriformis and cocygeus muscles and exits through the greater sciatic foramen at a location posterior to the sacrospinous ligament and just medil to the ischial spine (Barber, 2002; Maldonado, 2015). Thus, when injecting local anesthetic for a pudendal nerve block, the ischial spine serves an identifiable landmark (Chap. 25, p. 489). The pudendal nerve then runs beneath the sacrospinous ligament and above the sacrotuberous ligament as it reenters the lesser sciatic foramen to course along the obturator intern us muscle. Atop this muscle, the nerve lies within the pudendal canal, also known as Alcock canal, which is formed by splitting of the obturator internus investing fascia (Shafik, 1999). In general, the pudendal nerve is relatively fixed as it courses behind the sacrospinous ligament and within the pudendal canal. Accordingly, it may be at risk of stretch injury during downward displacement of the pelvic floor during childbirth (Lien, 2005).
he pudendal nerve leaves this canal to enter the perineum and divides into three terminal branches (Fig. 2-8). The first of these, the dorsal nerve of the clitoris, runs between the ischiocavernosus muscle and perineal membrane to supply the clitoral glans (Ginger, 2011 b). Second, the perineal nerve runs supericial to the perineal membrane (Montoya, 201l). It divides into
Ilioinguinal & genitofemoral nn. branches
Glans & crus of clitoriS sphincter mm.
/' Perineal membrane with window that exposes striated urogenital sphincter mm.
Dorsal n. & a. of
Perineal n. & a.
Perineal branch of cutaneous n.
Inferior rectal n. & a.
Gluteus maximus m.
FIGURE 2-8 Pudendal nerve and vessels. (Reproduced with permission from Corton MM: Anatomy. In Hoffman BL, Schorge JO, Bradshaw KD, et al (eds): Williams Gynecology, 3rd ed. New York, McGraw-Hili Education, 2016.) posterior labial branches and muscular branches, which serve the labial skin and the anterior perineal triangle muscles, respectively. Last, the inferior rectal branch runs through the ischioanal fossa to supply the external anal sphincter, the anal mucosa, and the perianal skin (vlahakkanukrauh, 2005). The major blood supply to the perineum is via the internal pudendal artery, and its branches mirror the divisions of the pudendal nerve.
The nonpregnant uterus lies in the pelvic cavity between the bladder anteriorly and the rectum posteriorly. Almost the entire posterior wall of the uterus is covered by serosa, that is, visceral peritoneum (Fig. 2-9). The lower portion of this peritoneum forms the anterior boundary of the rectouterine cul-de-sac, or pouch of Douglas. Only the upper portion of the anterior uterine wall is covered by visceral peritoneum. At the caudal border of this portion, the peritoneum relects forward onto the bladder dome to create the vesicouterine pouch. As a result, the lower portion of the anterior uterine wall is separated from the posterior wall of the bladder only by a well-defined loose connective tissue layer-the vesicouterine space. Clinically, during cesarean delivery, the peritoneum of the vesicouterine pouch is sharply incised, and the vesicouterine space is entered. Dissection caudally within this space lifts the bladder safely of the lower uterine segment for hysterotomy and delivery (Chap. 30, p. 573).