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14 Neurosurgical Interventions for Chronic Pain

14 Neurosurgical Interventions for Chronic Pain
The Massachusetts General Hospital Handbook of Pain Management

14
Neurosurgical Interventions for Chronic Pain

G. Rees Cosgrove and Emad Eskandar

Pain is the psychic adjunct of an imperative protective reflex.
—Sir Charles Sherrington

I. General considerations

1. Timing of neurosurgical interventions

2. Augmentative versus ablative procedures

3. Scope of neurosurgical manipulations

4. Variability of approach
II. Appropriate selection and evaluation of the neurosurgical pain patient

1. Medical workup and treatment

2. Malignant versus benign pain

3. Multidisciplinary team approach
III. Specific neurosurgical interventions encountered in pain practice

1. Ablative procedures

2. Augmentation procedures

3. Miscellaneous neurosurgical interventions
IV. Conclusion
Selected Readings

A multidisciplinary approach to patients with chronic pain is the best way to individualize treatment plans and optimize clinical results. Neurosurgical participation in the management plan is variable. In general, neurosurgical consultation is sought only after the patient’s pain has been proven refractory to all appropriate medical therapies. However, in some clinical situations, it is appropriate that neurosurgery be considered during the initial evaluation of the patient with chronic pain.
I. GENERAL CONSIDERATIONS
1. Timing of neurosurgical interventions
All patients should undergo a reasonable trial of conservative therapy before any neurosurgical intervention is discussed. Specifically, oral analgesics, parenteral agents, and usually short-term anesthetic interventions (e.g., local blocks, temporary spinal infusion catheters) should be tried as preliminary treatments. Enhancing the quality of life of the patient with chronic pain is paramount, and when it is clear that the overall goals of pain management are not being met by less invasive treatment, surgical approaches should be considered. In particular, early neurosurgical intervention can optimize function and greatly improve pain control during the final months of life in patients with terminal cancer. Surgical treatment for only the most debilitated patient reduces its functional benefit and increases the surgical risk. Unfortunately, there are no rules for when neurologic interventions are appropriate, and individual clinical situations must be carefully assessed.
2. Augmentative versus ablative procedures
Neurosurgical approaches to chronic pain can be loosely grouped into two broad categories: augmentative, when a device or substance is “added,” such as a pump system designed to infuse opiates or electrodes implanted for electrical stimulation, and ablative, when nervous input is severed, such as the many spinal cord lesioning techniques for treating chronic pain of malignant origin. Augmentative techniques have the advantage of being reversible: they can be discontinued if they prove ineffective, with no loss of function. Many augmentative procedures, however, suffer technical problems inherent in infusion pumps and chronic stimulator systems. They also require more regular and frequent follow-up visits. Research and development of biologic delivery systems may lead to improvements in this aspect of neuroaugmentation.
Ablative procedures for chronic pain carry with them the finality of neural tissue destruction as well as the potential loss of function that accompanies the destruction of nervous tissue. In addition, chronic pain frequently recurs months to years after an initially successful ablative procedure. In pain of malignant origin, where the patient’s life span is limited, this is less a concern than in pain associated with benign causes.
3. Scope of neurosurgical manipulations
Functional neurosurgical interventions for pain are directed at various levels of the nervous system, including the peripheral nerves, spinal cord, and brain. When selecting a surgical intervention, it is important to balance the potential benefit to the patient against the risk of loss of function. The technical requirements of the procedure, postoperative management issues, and the general condition of the patient must all be considered. Many pain complaints can be addressed by some neurosurgical intervention, but the important issue is: At what cost?
4. Variability of approach
There is no uniformity of approach in evaluating the pain patient for neurosurgical intervention. Although algorithms exist for choosing specific procedures designed to relieve specific complaints, each patient merits careful evaluation before a surgical procedure is even suggested. This way, unrealistic expectations can be prevented, while flexibility is maintained in designing a course of therapy best suited to the individual patient. Indeed, a given neurosurgical procedure used to treat identical complaints in different patients can produce vastly different results. For these reasons, we caution against a rigid approach to neurosurgical intervention.
II. APPROPRIATE SELECTION AND EVALUATION OF THE NEUROSURGICAL PAIN PATIENT
1. Medical workup and treatment
Before considering any procedure for pain control, it is extremely important to exclude an underlying treatable medical condition. Unrecognized causative pathology or correctable structural lesions must be excluded before any functional neurosurgical procedure is undertaken.
All candidates for neurosurgery require the usual preoperative evaluations for anesthetic management and surgery. Patients at high risk for surgery (e.g., those with end-stage malignancy) may be eager for intervention but may be unable to withstand the physiologic stresses of surgery. Medical optimization of the preoperative status may require manipulations not in accord with a patient’s wishes or with the approach of the care team. This situation can be avoided through the neurosurgeon’s early involvement with the patient who is difficult to manage on an oral or parenteral analgesic regimen.
2. Malignant versus benign pain
The common differentiation of pain into that of malignant or benign origin is clinically useful. In general, ablative approaches are more suitable for pain of malignant origin, when quality of life may be paramount to functional outcome. Ablative surgery for pain of benign origin, except for some specific conditions such as trigeminal neuralgia, is fraught with difficulties, especially when factors such as disability status, concurrent litigation, and psychosocial status dominate the clinical picture.
A second, more practical consideration is that patients who have benign pain and a normal life expectancy must be managed for decades after their surgical procedure. For example, the maintenance requirements for both the technical and emotional support of every patient can be significant after implantation of chronic stimulators in the spinal canal or drug infusion systems. This is not a major consideration for patients with progressive malignant disease.
3. Multidisciplinary team approach
The comprehensive pain service, with its neurologic, anesthesiologic, psychiatric, nursing, and social service components, remains the best resource for ensuring optimal patient care. Neurosurgeons who elect to treat chronic pain patients without this support network may find that the care of their patients is compromised. Similarly, the treatment of chronic pain is significantly hampered without the neurosurgeon’s input. Early involvement of the neurosurgeon with patients who respond poorly to conservative measures, with a careful evaluation of each patient’s needs and status, and deliberate review of all nonsurgical and surgical options will generally produce the best results.
III. SPECIFIC NEUROSURGICAL INTERVENTIONS ENCOUNTERED IN PAIN PRACTICE
1. Ablative procedures
(i) Peripheral ablative procedures
There is very little published information on peripheral neurotomy other than for the cranial nerves, except in the case of pain related to spinal facet innervation. Peripheral nerve lesions in the extremities can eventually result in a deafferentation pain syndrome. The procedure of choice for appendicular mononeuralgias is currently chronic stimulation, as described later. Results of facet denervation are variable, and although good results for chronic back pain have been reported, these have not been widely reproducible.
Surgical intervention for craniofacial pain syndromes has met with greater success. Trigeminal neuralgia can be treated with peripheral neurectomy with excellent results. Unfortunately, as in all peripheral lesions, nerve regeneration usually recurs, along with the pain syndrome. For these reasons, peripheral neurolytic procedures are generally not performed for chronic pain unless the patient’s life expectancy is extremely limited or the medical conditions are severe.
The craniofacial pain caused by trigeminal and glossopharyngeal neuralgia can be treated by percutaneous peripheral nerve or ganglionic ablation in the intracranial space. This is generally done by radiofrequency lesions (RFLs) or by injection of a sclerosing agent such as glycerol. The results of these ablations are variable, but in the case of RFLs for trigeminal neuralgia, initial pain relief followed by several years of comfort can be expected in 70% to 80% of patients. Open craniotomy and microvascular decompression or cranial nerve section is also an option for younger patients with craniofacial pain or for those who have failed percutaneous rhizotomy. The success rates of these interventions are similar but the operative risk is higher for open surgical procedures.
In recent years, focused radiosurgery has been utilized as a noninvasive method for controlling trigeminal neuralgia. A single focused dose of external radiation is directed at the trigeminal nerve root. This has provided encouraging, early control of trigeminal neuralgia, although long-term results have yet to be confirmed.
(ii) Spinal cord ablative procedures
The rationale for ablative lesions in and around the spinal cord is based on the anatomy of nociceptive pathways, from the periphery to the spinal cord with its central connections. The approach to spinal cord lesioning can be divided into lesions of the dorsal root ganglia, dorsal rootlets, dorsal root entry zone, crossing fibers of the spinothalamic tracts, and lesions of the ascending tracts (Fig. 1).

Figure 1. Cross-sectional view of the spinal cord showing approximate sites of common spinal cord ablative interventions—midline myelotomy, cordotomy, sympathectomy, dorsal root entry zone (DREZ) ablation, dorsal root ganglionectomy, and peripheral rhizotomy. STT, spinothalamic tract.

The dorsal ganglia can be surgically excised (ganglionectomy) in an open or percutaneous procedure, providing relief of pain in a roughly dermatomal distribution. This procedure must be performed at multiple levels but provides pain relief with concurrent loss of sensory input. Attempts have been made, with variable success, to limit the ablation to nociceptive input only. For defined pain of the thoracic or upper lumbar roots, this procedure can be of great benefit. The loss of sensation that accompanies the pain relief in these areas does not typically impart any significant functional difficulties.
Dorsal rhizotomy was one of the first operations used for pain control. Although generally effective, it is accompanied by complete sensory loss in the appropriate dermatomal distribution. Extensive dorsal root sectioning in an extremity leads to a useless limb and is not recommended. Partial or incomplete posterior rhizotomies have therefore been employed for certain chronic pain states and painful spasticity and have been especially useful in occipital neuralgia.
Deafferentation pain related to root avulsion or phantom limb pain has been successfully treated with an open operation to cause lesions in the dorsal root entry zone (DREZ). Small thermocoagulation lesions are made in the posterior spinal cord in the DREZ at multiple levels, presumably interrupting nociceptive pathways in Lissauer’s tract or destroying neurons of the substantia gelatinosa. Significant pain relief lasting several years has been achieved in a variety of chronic pain states, including postherpetic neuralgia. Early results are generally good but the recurrence of pain is common.
A variation on this theme is open microsurgical rhizidiotomy or DREZotomy, in which small, 2-mm lesions are placed into the ventral aspect of the DREZ under each rootlet. This procedure theoretically destroys the ventrolateral fibers, which are primarily nociceptive, while preserving the dorsal medial fibers ascending into the posterior columns, which are primarily somatosensory. The procedure has been especially useful for painful spasticity and chronic painful states of a single involved extremity.
The spinothalamic tract input from a specific dermatome crosses the midline of the spinal cord over several levels before ascending into the anterolateral aspect of the spinal cord as the lateral spinal thalamic tract. Localized bilateral pain, such as that seen with sacral tumors and pelvic malignant disease, can be addressed by midline (commissural) myelotomy. Good bilateral pain relief can be achieved, although the potential for functional loss is great. The high likelihood of postoperative neurologic deficit restricts this approach to pain of malignant origin in patients who already have functional disturbance (i.e., bladder and bowel dysfunction) preoperatively.
The procedure of interruption of the ascending lateral spinothalamic tract by either percutaneous or open anterolateral cordotomy has been used successfully for pain of malignant origin for many years. As with all ablations in the spinal cord, the risk of functional loss is real. Lower extremity pain is most easily approached by open thoracic cordotomy, and bilateral lesions can be performed. Bilateral cordotomy increases the risk of neurologic deficits, especially autonomic disturbance. Cordotomy at the cervical levels above the diaphragmatic input on one side and below it on the other (i.e., C3 and C6) can avoid complex postoperative respiratory difficulties (Ondine’s curse). For reasons that are unclear, pain often returns 1 to 2 years after cordotomy of either type. Repeat cordotomy at a higher level can be performed, although this is rarely needed if the procedure is restricted to patients with a limited life expectancy.
(iii) Central ablative procedures
Accurate lesioning of nociceptive pathways in the mesencephalon, diencephalon, and cortex has been greatly aided by technical advances in computed tomography (CT)- and magnetic resonance imaging (MRI)-guided stereotaxis. Long-term results, however, are disappointing and for these reasons the use of central nervous system ablative surgery is controversial and generally considered only for pain of malignant origin.
The general approach to deep brain lesioning is similar to that used in deep brain stimulation (see later). An electrode is placed into a stereotactically targeted site. The area is then stimulated as the electrode position is adjusted to achieve the desired effect. At this point, a lesion is created, or in the case of stimulation, the electrode is secured in place.
Lesioning the spinothalamic and secondary ascending trigeminal tracts in the midbrain (mesencephalotomy) can provide unilateral relief of head and neck pain. More rostral lesions in the medial thalamus (thalamotomy) can also provide unilateral or in some cases bilateral pain relief. A procedure for destroying the cingulate gyrus and bundle in the frontal lobe (cingulotomy) has also been used in cases of diffuse chronic pain associated with depression. These approaches should be reserved for the experienced functional neurosurgeon.
For reasons that are unclear, pain from hormonally responsive tumors that produce bony pain (carcinoma of the prostate and breast) is sometimes very amenable to pituitary ablation, either stereotactically or via a transsphenoidal approach. The sudden and complete relief of bone pain that is often evident even on emergence from anesthesia makes the procedure worth trying despite the expected postoperative endocrine deficits.
2. Augmentation procedures
(i) Peripheral nerve stimulation
Pain arising from a mononeuropathy may be treated by chronic stimulation, particularly when the pain is the result of nerve injury. Cancer pain has also been treated in this way but with less success. The long-term implantation of a stimulating electrode requires a significant investment of time and effort to manage the technical aspects of the device. Newer hardware designed for this purpose has simplified these techniques, but the clinical results are as yet unproven.
(ii) Spinal cord stimulation
Spinal cord stimulation (SCS) is frequently used for treating chronic pain, particularly of nonmalignant origin, because of its reversibility. It remains popular despite the high cost of the hardware and its maintenance. Spinal cord stimulators can be inserted percutaneously or during open procedures. The scientific basis for pain relief is unclear, although, as with peripheral nerve stimulation, the stimulation causes paresthesia within the painful area, which somehow modulates pain perception. Unfortunately, no specific markers have emerged of “best responders” to spinal cord stimulation. The best responders to date have been patients with failed back syndrome, lower-extremity pain of vascular origin, and other neurogenic pain syndromes. Published reports predict an approximately 50% long-term success rate overall for patients treated with SCS.
(iii) Deep brain stimulation
Deep brain stimulation (DBS) is confined to pain centers where there is significant interest in the procedure and a commitment to the management of patients with implanted stimulators. The two targets include the periaqueductal gray matter areas of the brainstem, and the nuclei ventralis posteromedialis and ventralis posterolateralis within the thalamus. Reports of DBS used for a variety of chronic pain states suggest that initial success is often followed by decremental effectiveness over time. Relief can be expected in 50% to 80% of patients initially, but the long-term results seem to indicate that only about half of DBS patients derive significant benefit. The most appropriate use of this technique appears to be in addressing chronic pain refractory to all other approaches in patients with a long life expectancy.
Finally, in patients with atypical facial pain or phantom limb pain, chronic stimulation of the motor cortex with subdurally implanted electrode arrays has demonstrated some encouraging results in these otherwise treatment-refractory cases.
(iv) Implantable infusion systems
The infusion of spinal epidural opiates or local anesthetic solutions is now an accepted and frequently used procedure for extremity and occasional truncal pain. The role of the neurosurgeon in the management of spinal infusion techniques is to offer the long-term surgical implantation of subcutaneously tunneled catheters leading to a reservoir, or the placement of catheters that exit the anterior abdominal wall that can be injected externally. In general, surgically implanted catheters have a longer life and lower complication rate.
Opiate infusion into the spinal intradural space or through the intraventricular route will always involve a neurosurgeon for catheter placement and avoidance of complications. It would appear that these intradural routes provide superior analgesia to epidural routes; however, there is an increased incidence of postoperative deficits and infectious complications and a risk of overdose. A spinal intradural or frontal intraventricular catheter can be adapted to any of several commercially available infusion systems. Since excellent short-term pain relief is achieved after relatively minor surgery, intradural therapy should probably be utilized more frequently.
3. Miscellaneous neurosurgical interventions
(i) Trigeminal and glossopharyngeal neuralgia
The neurosurgical approach to trigeminal and glossopharyngeal neuralgia includes percutaneous rhizotomy, open partial cranial rhizotomy, and microvascular decompression. These treatments are described in Chapter 12 (II, 5). For any patient who has a trigeminal pain syndrome that is not controlled well by medication, the likelihood of satisfactory pain relief without medication is approximately 90% for any of these approaches. Recurrent trigeminal neuralgia can also be treated with repeat rhizotomy with good relief. Complication rates are extremely low for these procedures, but the specific procedure recommended must be tailored to each patient’s needs and risks.
(ii) Low back pain
Low back pain is a problem commonly encountered by the neurologist and the neurosurgeon. In particular, the failed back syndrome is a frequent management problem for the pain service. Most of these patients can be managed with an aggressive medical regimen, but a detailed evaluation of patients with a failed back should be considered, as with any other pain syndrome. In carefully selected patients with continued underlying spinal structural pathology, reasonable success has been achieved with reoperation for recurrent disc disease or continued nerve root compression. In addition, spinal cord stimulation or epidural opiate infusion can be of value in those patients who have failed all other forms of therapy.
(iii) Sympathectomy
Sympathectomy for autonomic and visceral pain is now almost exclusively performed by the anesthesiologist via percutaneous approaches. For specific cases of reflex sympathetic dystrophy (RSD), surgical sympathectomy may be necessary because of the difficulty in achieving adequate technical results percutaneously. The advantage of open sympathectomy is the excellent anatomic definition of the lesion. However, pain recurrence is as likely to occur after sympathectomy performed in an open fashion as after percutaneous approaches. Selective peripheral nerve stimulation has also been used for RSD confined to a single nerve distribution or extremity.
IV. CONCLUSION
Although the surgical treatment of chronic pain should always follow a reasonably exhaustive trial of conservative medical approaches, there is a role for surgical intervention in many chronic pain patients. The neurosurgeon’s participation in the overall treatment plan of the patient with chronic pain provides an opportunity for early surgical intervention, before worsening of the disease or frustration with lack of progress renders neurosurgical intervention impossible. A judicious approach by the referring pain specialist, as well as frank discussions with the patient, family, and care providers, is likely to yield the best results for a patient who has not responded to medical management. Unfortunately, multiple factors and individual variability still render the surgical outcome for each patient somewhat difficult to predict.
As for all patients with chronic pain, the entire multidisciplinary pain service should take responsibility for preoperative and postoperative care. No one specific neurosurgical intervention will totally relieve persistent pain; it should be considered only as a single therapeutic option in the overall treatment plan. The management of chronic pain can, at times, be greatly improved by timely, selective neurosurgical interventions to provide an excellent quality of life in the face of intercurrent disease and chronic pain.
SELECTED READINGS

1.
Burchiel KJ, ed. Pain surgery. New York: Thieme, 1999.

2.
Gybels JM, Sweet WH. Neurosurgical treatment of persistent pain. In: Pain and headache, vol 11. Basel: Karger, 1989.

3.
Schmidek HH, Sweet WH. Operative neurosurgical techniques: Indications, methods, and results, 3rd ed. Philadelphia: WB Saunders, 1995.

4.
Tasker RR. Neurosurgical and neuroaugmentative intervention. In: Patt RB, ed. Cancer pain. Philadelphia: Lippincott, 1993.

5.
Tasker RR. The recurrence of pain after neurosurgical procedures. Qual Life Res 1994;3:S43–49.

6.
Wall PD, Melzack R, eds. Textbook of pain, 3rd ed. New York: Churchill-Livingstone, 1989.

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