Neurosurgical Pain Management

Ramin Amirnovin

Rees G. Cosgrove

Emad N. Eskandar

It is easier to find men who will volunteer to die, than to find those who are willing to endure pain with patience.

—Julius Caesar

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 short-term anesthetic interventions (e.g., local blocks and temporary spinal infusion catheters) should be tried as preliminary treatments. Enhancing the quality of life of a 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. Early neurosurgical intervention can optimize function and can greatly improve pain control during the final months of life in patients with terminal cancer. Reserving surgical treatment for only the most debilitated patients reduces its functional benefit and increases the surgical risk. Unfortunately, there are no hard and fast rules about timing for surgical interventions, and individual clinical situations must be carefully assessed.

2. Augmentative Versus Ablative Procedures

Neurosurgical approaches to chronic pain are grouped into two categories: augmentative (where a device or substance is implanted) and ablative (where neural tissue is destroyed).
Augmentative techniques have the advantage of being reversible so that they can be discontinued if they prove ineffective, without loss of function. However, such procedures suffer from technical problems inherent in the infusion pump and stimulator systems. The patients undergoing these procedures also require more frequent follow-up visits. Ablative procedures are characterized by the finality of neural tissue destruction and, hence, the potential loss of function. Furthermore, most of these procedures are less successful in long-term pain control than augmentative methods are. By evaluating the patient’s needs in the light of the risks and benefits, one can choose the proper type of procedure for a specific patient. For instance, in pain from malignancy, the patient’s life span is limited, and, hence, a definitive ablative procedure may be more appropriate.

3. Scope of Neurosurgical Manipulations

Neurosurgical interventions for pain can be directed at the peripheral nerves, spinal cord, or the brain. When selecting an intervention, it is important to balance the potential benefit against the risk of loss of function. Also, the technical requirements of the procedure, postoperative management issues, and the general condition of the patient must be considered. Many pain complaints can be addressed by a neurosurgical intervention, but the important question is: At what cost?

4. Variability of Approach

Although algorithms exist for choosing specific procedures designed to relieve specific complaints, each patient merits careful evaluation before a procedure is suggested. This approach prevents unrealistic expectations, while maintaining flexibility in designing a course of therapy suited to the individual. A given neurosurgical procedure used to treat identical complaints in different patients can produce vastly different results. Hence, we caution against a rigid approach to neurosurgical intervention. A multidisciplinary approach to chronic pain is the best way to individualize treatment and optimize results.

II. APPROPRIATE SELECTION AND EVALUATION OF THE PATIENT WITH NEUROSURGICAL PAIN

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 to ensure safety during anesthesia and surgery. Patients at high risk for surgery may be eager to undergo an intervention but may be unable to withstand the physiologic stress of surgery. Medical optimization of the preoperative status may require manipulations that are not in accord with a patient’s wishes or with the approach of the care team. Such situations can be avoided in patients in whom it is difficult to control pain with a medical regimen by the early involvement of a neurosurgeon.

2. Malignant Versus Benign Pain

The common differentiation between pain of malignant and that of benign origin is clinically useful. In general, ablative approaches are more suitable for pain of malignant origin, when quality of life may be paramount. Ablative surgery for pain of benign origin, except for some specific conditions such as trigeminal neuralgia (TGN), 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 taken care of for decades after their surgical procedure. For example, the maintenance requirements for both the technical and emotional support of every patient can be important after implantation of chronic stimulators in the spinal canal or drug infusion systems. The maintenance requirements are not major considerations 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 patients with chronic pain 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, along 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.

II. SPECIFIC NEUROSURGICAL PROCEDURES

1. Ablative Procedures

In the past decade, most ablative procedures have been replaced by augmentative procedures. We only discuss the ablative procedures that are still in use.

(i) Peripheral Ablative Procedures

Peripheral nerve lesions in the extremities can result in deafferentation pain, but the procedure of choice for these appendicular mononeuralgias is chronic stimulation (as described in subsequent text) rather than ablation. In contrast, ablation provides good results for craniofacial pain syndromes, specifically TGN and glossopharyngeal neuralgia (GPN).

In treating TGN in an older or frail patient, the ablation of the trigeminal nerve yields acceptable results given the limited life-expectancy of this population. Three methods can be used to ablate the trigeminal nerve. The first two methods involve the percutaneous introduction of a needle (under fluoroscopic guidance) into the foramen ovale. Then, a heat-producing radiofrequency electrode or the injection of alcohol is used to produce a lesion on the trigeminal ganglion. These methods yield a 70% to 80% success rate at 6 years and a less impressive 30% success rate at 12 years. The third method of lesioning the trigeminal
ganglion is by radiosurgery. Application of 80–Gy radiation to the proximal trigeminal nerve reportedly yields a success rate of 70% at 1 year, which declines to 56% by 5 years. Unlike the percutaneous radiofrequency or alcohol lesions, the effect of radiosurgery is not immediate, but rather takes 2 to 6 months to occur. The ablative procedures for TGN share a low rate of anesthesia dolorosa (pain despite sensory loss), which is the most common complication. For younger, less frail patients, microvascular decompression (MVD) can provide a higher long-term success rate (see subsequent text).

Currently, the first-line therapy for GPN is MVD, but, in patients in whom this fails, a craniotomy is occasionally performed for sectioning of cranial nerve IX (glossopharyngeal) and the upper division of X (vagus). Outcomes have not been systematically studied because the procedure is rarely performed.

Dorsal rhizotomy (sectioning of the dorsal root) was one of the first operations used for pain control, and, although generally effective, it is also accompanied by sensory loss in the associated dermatome. Extensive dorsal root sectioning in an extremity leads to a useless limb and is not recommended. Partial or incomplete posterior rhizotomies have been employed for chronic pain of the thorax and painful spasticity, and have been especially useful in occipital neuralgia. The procedure provides pain control in 70% of the patients immediately after surgery, but only 28% of the patients receive long-term benefits. This difference is felt to be due to the poor localization of the involved nerve roots. Recent studies have confirmed that pain control can be improved by using the somatosensory evoked potentials (SSEP) during the procedure to guide lesioning of the correct dorsal root(s).

(ii) Spinal Cord Ablative Procedures

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