Intrathecal neurolytic blocks are performed with either 95% alcohol or with 6-8% phenol in glycerin. Alcohol is hypobaric and phenol hyperbaric compared with the cerebrospinal fluid; positioning of the patient must therefore be done accordingly. This is a report about 67 consecutive neurolytic alcohol blocks of the lower sacral roots. Although lumbar puncture is done at the lowest possible level at L5-S1, the block only affects the roots from S3 or S4 downwards. The detailed anatomy of the caudal dural sack reveals why S1 and S2 are not affected. S1 and S2 contribute to the lumbosacral plexus and are important for the innervation of the lower extremities. However in patients with very low CSF pressure, S2 and S1 might become damaged. This is the most important result of this series. To avoid an unexpected extension of the block in patients with very low CSF pressure, we now recommend that synthetic CSF be instilled prior to alcohol. The results were unsatisfactory in patients with perineal pain and pain in the lower extremities as well. In these cases S2 or S2 + S1 are already affected by the tumor. One should employ other therapeutic procedures (e.g., epidural morphine) for these patients. After careful selection of patients, alcohol neurolysis of the lower sacral roots is a useful procedure.
Porges, Zdrahal, , , , , , , (1985). [Intrathecal alcohol neurolysis of the lower sacral roots in inoperable rectal cancer]. Der Anaesthesist, 1985 Nov;34(11):627-9. https://www.ncbi.nlm.nih.gov/pubmed/2418708