Pudendal nerve between sacrospinous and sacrotuberous ligament. (Reprinted with permission from Philip Peng Educational Series)
It gives off three terminal branches: the dorsal nerve of the penis or clitoris, inferior rectal nerve, and the perineal nerve (Fig. 9.2). Common sites of compression are at the ILP and within the Alcock’s canal.
The pudendal nerve contains both motor and sensory fibers. The inferior rectal nerve supplies the external anal sphincter (Fig. 9.3). The remaining portion of the pudendal nerve trunk becomes the perineal nerve, which continues to supply sensation of the skin of the penis (clitoris), perianal area, and the posterior surface of the scrotum or labia majora. The perineal nerve also provides motor supply to the deep muscles of the urogenital triangle.
Inferior Cluneal Neuralgia
Patientwith pain from inferior cluneal nerve (ICN) entrapment typically presents with pain in the lower buttock associated with perineal pain. On detailed assessment, the perineal pain is mainly in the lateral perineum. The ICN is a branch from posterior femoral cutaneous nerve of the thigh and shares the common trunk with perineal ramus (PR). It should be considered as one of the differential diagnoses of pudendal neuralgia.
The PR branch runs a horizontal course following the inferior edge of the ischial tuberosity to reach the perineum. In its course under the ischium and behind the hamstring muscles, the PR moved along in a fatty and fibrous corridor, which is susceptible to entrapment or injury. Also, injury to hamstring origin may cause irritation to this nerve as well. From there, the PR divides into branches to the lateral part of the anal margin and the labia majora or scrotum (left sonogram). The ICN follows the deep surface of the gluteus maximus muscle, and at the lower border of the same muscle, it perforates the gluteus maximus fascia and spreads out inside it and reaches the skin of the lower gluteal region to supply the lower buttock region (Fig. 9.4).
Pudendal Entrapment Neuropathy
The diagnosis of PNE remains primarily clinical. There are no pathognomonic imaging and laboratory or electrophysiology investigations available for confirmation. Clinical criteria (Nantes criteria) have been established but are not accepted universally. The Nantes criteria are composed of four domains: essential criteria for the diagnosis of pudendal neuralgia, complementary diagnostic criteria, exclusion criteria, and associated signs not excluding the diagnosis. From the essential criteria, diagnostic nerve block plays an important role in the diagnosis.
Pain in the territory of the pudendal nerve: from the anus to the penis or clitoris.
Pain is predominantly experienced while sitting.
The pain does not wake the patient at night.
Pain with no objective sensory impairment.
Pain relieved by diagnostic pudendal nerve block.
Inferior Cluneal Neuralgia
Patient with ICN entrapment is diagnosed on clinical ground with the use of diagnostic nerve block. The typical presentation is burning pain aggravated by sitting in the lower and medial aspect of buttock, the posterior and proximal aspect of the thigh, the lateral part of anal margin, and the skin of the labia majora/the scrotum. Detailed assessment may reveal sensory changes in the lower buttock and the pain restricted to the lateral part of perineum, at least in the initial presentation. Pressure on the ischial tuberosity provokes pain in similar region. Some patient may have pathology in hamstring origin as the PR courses the hamstring before innervating the perineum.
This is differentiated from pudendal neuralgia in that these pains are caused by the sitting position on a hard seat and provoked by the compression of the nerves against the ischial tuberosity and the hamstring muscle insertions. Pain in pudendal neuralgia is in the perineum (anus, penis, clitoris), aggravated by the sitting position on a soft seat or a bicycle seat and provoked by the compression of the soft parts of the perineum or against the Alcock’s canal and ishcial spine.
Ultrasound Scan (Pudendal Nerve)
Probe: Curvilinear 2–6 MHz
Scan 1: Over the iliac crest
The key landmark is the posterior superior iliac spine (PSIS). The structures will be iliac crest with three layers of gluteus muscles in view (Fig. 9.5).