A unique variation of the pudendal nerve

The pudendal nerve (PN) arising from the ventral primary rami of the second, third, and fourth sacral plexus (S2, S3, and S4) exits the pelvic cavity under the piriformis muscle through the greater sciatic foramen and descends ventral to the sacrotuberous ligament (STL), and then travels ventrally through the pudendal canal, splitting into three branches: the inferior rectal branch, the perineal branch, and the dorsal sensory nerve of the penis or clitoris (Shafik et al., 1995; Mahakkanukrauh et al., 2005). During a routine gross dissection of a 74-year-old Japanese female cadaver, who had died from ovarian carcinoma, it was noted that the bilateral partial PN penetrated the STL and then passed on the ischial tuberosity, which this nerve branches was called ‘‘accessory pudendal nerve (APN)’’ in next description. In the left gluteal region, the APN originated primarily from the rami of S2 gained contributions from the adjacent roots of S1 and S3. The nerve accompanied the PN before running adjacent to the STL, then directly penetrated the STL from the ventral to dorsal aspect, and then passed on the ischial tuberosity, then split into two branches; a main branch supplied the dorsum of the clitoris, and another thin branch joined to supply the area of the posterior femoral cutaneous nerve (Fig. 1). In the right gluteal region, the APN originated from the S2 and S3 gaining contribution from the S1, and divided into two branches before passing through the STL. Thin rami penetrated the STL from the right to the left border, and then joined the PN supplying the perineal area and the clitoris, but without passing through the pudendal canal. A main branch of the APN directly pierced the STL from the ventral to dorsal aspect in the mid-position of the STL, and then split into three branches. A dominant branch of the APN supplied the region of the dorsal nerve of the clitoris and two thin rami supplied areas of the perineum and the posterior femoral cutaneous nerve, respectively (data not shown). Clinically, chronic perineal pain, or so-called idiopathic perineal pain in the seated position, has been most reported (Robert et al., 1998; Ramsden et al., 2003; Loukas et al., 2006). Generally, it is due to piriformis syndrome (Barton, 1991), or the falciform process of the STL (Loukas et al., 2006). Robert et al. (1998) examined the anatomic basis for chronic perineal pain and the role of the PN in 12 fresh cadavers, and identified three possible conflicting settings: in the constriction between the STL and sacrospinous ligament, in the pudendal canal, and while straddling the falciform process of the STL. Mahakkanukrauh et al. (2005) performed an anatomical study of the PN adjacent to the sacrospinous ligament in 37 cadavers using 73 side samples, and described a type of the PN that is two-trunked with one trunk as an inferior rectal nerve pierces through the sacrospinous ligament (type III, 8/73; 11%). Loukas et al. (2006) described the relationship between the PN and the STL in 50 cadavers, 100 side samples, emphasizing the presence of the falciform process of the STL, and its relevance in PN entrapment syndrome. However, we could find no reports in the literature of PN branches passing through the STL and over the ischial tuberosity, as the present case. The variation of the PN may be related to the intractable perineal pain in the seated position. In addition, as the origin and innervating regions of the redundant branches of the PN, we called the nerve the ‘‘APN’’.