Anatomical basis of transgluteal pudendal nerve block

The pudendal nerve may become entrapped either within the pudendal canal or near the sacrotuberous ligament resulting in a partial conduction block. The goal of the present anatomical study was to assess a new transgluteal injection technique in terms of the precise injection site and the resulting distribution of the injected agent.

This study was carried out using eight fresh human cadavers. An epidural needle with a removable wing was inserted and the catheter position visualized using MRI. Through the catheter 10 ml of gadolinium contrast medium was injected into three of the cadavers. A further four cadavers were injected with latex and blue pigment and the pelvi-perineal area of each then separated from the trunk for freezing before being cut into 4-8 mm thick sections with an electric bandsaw. One final cadaver was injected with a mix of gadolinium (5 ml) and latex (5 ml) and both the MRI and anatomical procedures outlined above were performed.

Using MRI, we clearly imaged both the site of injection, near the trunk of the pudendal nerve, and the gadolinium contrast medium in different pelvic and perineal areas and around the fascia of the obturator internus and levator ani muscle. Concerning the anatomical study, latex was observed mainly around the sacrotuberous ligament, along the obturator internus muscle and in the perineal area in contact with the dividing branches of the pudendal nerve. The mixed injection of latex and gadolinium in the pudendal canal was found with the same localization between MRI and anatomical studies.

This easily performed technique should provide a new approach for treating perineal neuralgia via pudendal nerve block in the consultation room without the need for computed tomography.