The pelvic portion of each sympathetic trunk is situated in front of the sacrum, medial to the anterior sacral foramina. It consists of four or five small sacral ganglia, connected together by interganglionic cords, and continuous above with the abdominal portion. Below, the two pelvic sympathetic trunks converge, and end on the front of the coccyx in a small ganglion, the ganglion impar, also known as azygos ^[1] or ganglion of Walther.

Clinical significance

A study found that in some cases a single injection of nerve block at the ganglion impar offered complete relief from coccydynia.^[2]