Anatomy and physiology of pudendal pain

摘要

abstract_textpPudendal pain stems from the perineum and involves the nerve trunk and somatic nerves. It emanates from the affected nerve and depends on the body's position; the seated position compresses the nerve. The anatomy and physiology of this type of pain calls for an emphasis on several points: a) delineation and innervation of the perineum; b) understanding the relevant pain pathways; c) knowledge of the inhibitory structures throughout the pathways. The perineum: in the embryo, it is located in the infralevator region, containing the erectile organs, sphincters and fatty tissue. It extends from the genitals to the anus. Innervation of the perineum is varied: the pudendal nerve extends from S-3 nerve roots and provides cutaneous and striated muscle innervation. It contains a large number of orthosympathic fibres that run along the laterovertebral chain. The pelvis is located in the supralevator region, contains the pelvic viscera and is exclusively innervated by the autonomic nervous system. The pain pathways come from the three embryonic germ layers. Exteroceptive pain (cutaneous) reaches the top of the posterior grey horn; proprioceptive fibres (muscles, fascia, and tendons) extend to the isthmus; interoceptive fibres (viscera) run to the base. The converging neurons of Rexed's lamina V collect pain information in the dorsal (DST) and ventral (VST) spinothalamic tract. In the brain stem, the DST slowly rises, later reaching the thalamus. Many fibres will be stopped in the reticular formation. The VST becomes a satellite of the lemniscal pathway and quickly reaches the thalamus with it. In the ventroposterolateral (VPL) nucleus of the thalamus, the DST projects into the prefrontal cortex, giving pain its quantitative dimension. Arriving first, the VST immediately projects into the postcentral gyrus to localize the pain. At the same time, the hypothalamus, receiving information from the reticular formation, responds to the feeling of pain with the release of a stream of hormones. The limbic cortex, drawing its information from the neocortex, may store the pain in memory, adding an emotional component. The visceral pain pathways are similar to those for somatic pain in the central nervous system. Knowing their extra-axial component makes it possible to position infiltrations (rami communicans). Inhibitory structures exist at all levels: gate control in the spinal cord, reticular and thalamic filters, inhibitory systems and the motor neocortex. When etiopathological treatment fails, knowledge of these structures makes it possible to employ neurostimulation techniques. When faced with perineal pain, understanding anatomy will sometimes lead to the diagnosis of a somatic, nerve trunk disorder, avoiding the reflex of implicating visceral structures outside the perineum and developing inappropriate therapeutic strategy./p/abstract_text