Dorsal Rhizotomy

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Initial posting from: Bernard Bendok, MD

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Dorsal rhizotomy has a limited role in the treatment of cancer and some non-cancer pain syndromes. It belongs to a group of interventions including cordotomy, sympathectomy, and intrathecal morphine pumps available to patients who have failed oral analgesia. The procedure has a long history beginning with Abbe, who was the first clinician to use dorsal rhizotomy for pain control in 1896. Suitable cancer patients are those with brachial plexus, pelvic, or thoracic involvement. Non-cancer patients with occipital neuralgia, facet arthropathy or useless limp pain, and allodynia may also benefit. A trial of anesthetic nerve root blockade must be attempted before permanent lesioning. Rarely, anesthetic may enter the subarachnoid space requiring resuscitation of the patient. Compliations of the actual procedure include deafferentation pain, spinal cord infarction, and sensory loss to functional areas.

Technique

Localizing pain to the proper root is important, especially near functionally intact dermatomes or myotomes. Yet due to overlap innervation, lesioning 3-4 adjacent roots is often necessary to achieve hypesthesia. Rhizotomy may be performed within or external to the dura. In the former, the dura is opened following a standard laminectomy and roots are identified and severed with clips or electrocautery. Blood vessels should be preserved to minimize the risk of spinal cord infarction, especially at thoracic levels. Facetectomy and foraminotomy are carried out in the extradural technique, followed by exposure and transection of white dorsal roots within their dural sheath. Motor roots may lie in close proximity and should be preserved. For sacral involvement, the entire thecal sac is transected between S1 and S2 roots. Unmyelinated and small myelinated fibers are selectively sensitive to thermal ablation. Percutaneous radiofrequency rhizotomy takes advantage of this feature and offers a less invasive approach. Under fluoroscopic guidance, an electrode is passed into neural foramina and stimulated for 1-2 minutes. Heat from the electrode dissipates and lesions adjacent roots.

Outcomes

Dorsal rhizotomy can be very effective in relieving both cancer and non-cancer pain, although results are varied. The fact that ventral roots carry some unmyelinated nociceptive afferents may help explain this. Certain types of pain seem to respond better than others, including pelvic cancer pain (caveat: procedure eliminates bowel, bladder, and sexual function) and occipital neuralgia. Rhizotomy for failed back syndrome has shown disappointing results.

References

  1. Abbe R: Intradural section of the spinal nerves for neuralgia. Boston Med Surg J 135: 329-335. 1896
  2. Coggeshall RE: Afferent fibers in the ventral root. Neurosurgery. 4:443-448, 1979
  3. Young RF: Dorsal rhizotomy and dorsal root ganglionectomy . In Youmans JR (eds): Neurological Surgery, vol. 5, 4th ed. Philadelphia, WB Saunders, 1996, pp 3442-3451.
  4. Tzaan WC, Tasker RR. Percutaeous radiofrequency facet rhizotomy--experience with 118 procdedures and reappraisal of its value. Can J Neurol Sci. 2000 May;27(2):125-30.
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