One is the loneliest number: a review of the ganglion impar and its relation to pelvic pain syndromes.

The ganglion impar is often overlooked as a component of the sympathetic nervous system. Despite its obscurity, this ganglion provides a pathway for neurons by accommodating postganglionic sympathetics, visceral afferents, and somatic fibers traveling to and from the pelvis. Its classic anatomic location as described in the 1720's held up until recently, with the current literature now revealing a great deal of anatomical variability. This variation becomes important when the ganglion impar is used as a treatment target for patients with chronic pelvic pain - its primary clinical implication. The aim of this review was to provide a better understanding of the anatomy of ganglion impar, accounting for variation in size, shape, and location. In addition, the clinical importance and treatment modalities associated with the ganglion impar are outlined.