Sacral Nerve Block

Indications and Clinical Considerations

Sacral nerve block is useful in the evaluation and management of radicular and perineal pain that is believed to be subserved by the sacral nerves. This technique also is useful as an adjunct to provide surgical anesthesia when prior caudal or lumbar epidural block is spotty.

Sacral nerve block via the transsacral approach with local anesthetic can be used as a diagnostic tool when performing differential neural blockade on an anatomic basis in the evaluation of radicular or perineal pain. If destruction of the sacral nerves is being considered, this technique is useful as a prognostic indicator of the degree of motor and sensory impairment that the patient may experience. Sacral nerve block via the transsacral approach with local anesthetic may be used to palliate acute pain emergencies, including postoperative pain relief after transperineal and bladder surgery while waiting for pharmacologic methods to become effective in those patients who would not tolerate the sympathetic block associated with lumbar epidural anesthesia. Sacral nerve block via the transsacral approach with local anesthetic and steroid is occasionally used in the treatment of sacral root or perineal pain when the pain is believed to be secondary to inflammation or when entrapment of the sacral nerve is suspected. Sacral nerve block via the transsacral approach with local anesthetic and steroid also is indicated in the palliation of pain associated with diabetic neuropathy and is useful in the treatment of bladder dysfunction after injury to the cauda equina. Destruction of the sacral nerves via the transsacral approach is occasionally used in the palliation of persistent perineal pain secondary to invasive tumor or bladder dysfunction mediated by the sacral nerves and has not responded to more conservative measures.

Clinically Relevant Anatomy

The convex dorsal surface of the sacrum has an irregular surface secondary to the fusing of the elements of the sacral vertebrae. Dorsally, there is a midline crest called the median sacral crest ( Fig. 145.1 ). Eight posterior sacral foramina allow the passage of 4 pairs of the primary posterior divisions of the sacral nerve roots ( Fig. 145.2 ). The posterior sacral foramina are smaller than their anterior counterparts. Leakage of drugs injected onto the sacral nerves through the posterior neural foramina is effectively prevented by the sacrospinal and multifidus muscles. The fifth sacral nerves exit the sacral canal via the sacral hiatus. The sacral nerves provide sensory innervation to the anorectal region and motor innervation to the external anal sphincter and levator ani muscles. The second through fourth sacral nerves provide the majority of visceral innervation to the bladder and urethra as well as the external genitalia ( Fig. 145.3 ).