The ganglion impar (ganglion of Walther) is the single sympathetic ganglion where the two sympathetic trunks meet at their lower end. It lies in front of the sacrococcygeal junction or the upper coccyx, behind the rectum. It is the only unpaired ganglion of the sympathetic trunk.
| Origin | Fusion of the lower ends of the right and left sympathetic trunks |
|---|---|
| Course | Lies in the retroperitoneum in front of the sacrococcygeal junction, behind the rectum, and sends grey rami to the coccygeal nerves |
| Motor |
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| Sensory |
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Ganglion impar block, usually performed with a needle through the sacrococcygeal joint under imaging, is used for pain in the perineum, anus and distal rectum, especially from cancer, and for chronic coccydynia. Because the ganglion receives visceral and sympathetic fibres from these structures, blocking it can relieve burning, poorly localised perineal pain. The rectum lies just in front, so needle position must be checked carefully.
Pelvic cancer or chronic coccygeal problems can cause vague burning pain in the perineum, which may respond to local anaesthetic or neurolytic block of the ganglion impar.
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