Destructive interventions on the nervous system are a valuable method to obtain control of otherwise intractable pain. Before the relatively recent development of augmentative techniques, such as intrathecal drug delivery and electrical neurostimulation (both peripheral and central), these were the mainstay of neurosurgical pain treatment. Options exist for lesioning the nervous system at multiple levels, including the brain and brainstem, cranial nerves, spinal cord, and peripheral nerves. Although the rise of these newer therapies has pushed aside many ablative procedures, these are still valuable components of the neurosurgical armamentarium.
The interruption of peripheral or central nervous system (CNS) pathways carrying pain has always seemed the most direct and logical manner to solve the problem of medically intractable pain, whether benign or malignant in origin. The targets for these interventions include the peripheral nerves and ganglia, the ascending spinothalamic tract and central aspects of the spinal cord, and the trigeminothalamic tract. Supratentorial structures such as the thalamus and cingulate gyrus have also been destroyed in the quest for pain control. Unfortunately, the results of these interventions have not been as straightforward as the theories behind them use, again demonstrating that the physiology underlying the development and maintenance of chronic pain is more complex than we understand.
Several methods have been used to lesion the nervous system. The easiest is a simple mechanical interruption via avulsion, transaction, or resection of a peripheral nerve, a cranial nerve branch, a ganglion, or a segment of the spinal cord. Thermocoagulation or radiofrequency (RF) lesioning has been most often used in the CNS, including the creation of ganglionic, spinal cord, and intracerebral lesions. Cryoablation found some favor in the mid 20th century but is rarely used today. Other alternatives include laser, radiation, and focused ultrasound.
Patients selected for these procedures should have chronic pain that has failed to adequately respond to multiple other conservative nonsurgical treatments. These prior treatments should include rehabilitation, oral medications (anti-inflammatories, opioids, anticonvulsants, antidepressants), and injections. Given the advances in neurostimulation and intrathecal drug delivery, it is also reasonable to conduct a trial of these therapies before considering ablative procedures. This is true both for patients with pain from late stage malignancies (because of their higher medical risk in undergoing surgery) and those with pain from nonmalignant causes (because of the risk of permanent neurologic morbidity from the procedures).
It is just as important to carefully select the correct ablative procedure for the patient, considering both the etiology of the pain and its location within the nervous system, so as to maximize the chance of achieving pain relief. For instance, central neuropathic pain is not expected to respond well to a peripheral neurectomy or dorsal root ganglion lesion.
This chapter reviews the published experience with several neuroablative procedures, beginning with those that are still most commonly in use. Certain destructive procedures (e.g., trigeminal ganglionic lesions and spinal facet denervation) are not included in this chapter.
The dorsal horn of the spinal cord serves as both a relay center and an integration site for sensory signaling. Sindou and Jeanmonod1 (via coagulation in 1972) and Nashold and Ostdahl2 (via RF energy in 1974) pioneered lesioning of the dorsal root entry zone (DREZ) of the spinal cord as a method of removing the portions of the CNS that had already undergone central sensitization in response to a peripheral lesion, such as malignancy or nerve injury. The lesions are intended to destroy Lissauer’s tract and preserve fibers subserving proprioception and certain aspects of touch that travel in the dorsal rootlets to the dorsal columns. It continues to have clinical application primarily for the treatment of pain caused by traumatic brachial plexus root avulsions.
In this procedure, the intended anatomic levels are exposed first via complete laminectomy or hemilaminectomy and dural opening. Microsurgical dissection of the dorsal rootlets (if they are present) is performed to separate and isolate them from each other. If the rootlets are absent, a line is drawn between existent rootlets above and below the avulsion level. After the correct anatomic levels are identified, either by electrical stimulation or the absence of avulsed rootlets, lesions are created on the inferolateral aspect of the rootlet entry zone. The small, lightly myelinated or unmyelinated fibers that carry pain signals to the dorsal horn enter from the lateral aspect of the DREZ while the medial side contains primarily fibers destined for the dorsal columns. Lesions are created either by coagulating and opening the pia on the lateral aspect of the dorsal rootlets followed by microbipolar coagulation of the DREZ (Sindou’s method) or by using a DREZ RF needle (0.25 mm diameter) to make 1-mm-spaced lesions at 75°C for 15 seconds. Laser3 and ultrasonically4 created lesions have also been described.
For the treatment of facial pain, the lesions may be made in the trigeminal nucleus caudalis (so-called nucleus caudalis DREZ lesions). This is essentially a cranial continuation of the dorsal horn, extending from the brainstem down into the upper cervical spinal cord, and receives much of the nociceptive signaling from the trigeminal system. As pioneered by Bernard et al.5 based on the initial work of Sjoqvist,6 these lesions are made from the upper rootlets of C2 to a point just above the obex. In the nucleus caudalis, cells receiving input from the first division are located in a more ventrolateral position, and cells receiving input from the third division are located in a more dorsomedial position. Moreover, following so-called “onion-skin” distribution, perioral sensation is only represented in the more cranial aspect of the nucleus while representation of the more lateral aspects of the face is located below the level of the obex down to C2.7
Great care must be exercised in targeting DREZ lesions because of the presence of the corticospinal tract just lateral to the dorsal horn. Moreover, the size and angulation of the DREZ and dorsal horn vary depending on the spinal level, being much thinner in the thoracic region. Moreover, the inherently tenuous vascular supply to the spinal cord must not be disrupted. Motor complications range from 0% to 69%.8
Percutaneous trigeminal tractotomy may be done with the help of computed tomography (CT) guidance;9 it represents a less invasive alternative for open caudalis DREZ procedure. Here the trigeminal tract and nucleus caudalis are approached via percutaneously inserted needle that is placed at occipital–C1 interspace, entering skin 1 to 2 cm off the midline with the patient in a prone position. The RF electrode is inserted into the uppermost aspect of the spinal cord, and the RF thermal lesion is performed after testing somatotopy of the nucleus by electrical stimulation.9
Larger series show reasonable rates of pain control. Dreval published results of 124 patients with brachial plexus avulsion pain followed a mean of 47.5 months after DREZ and reported an 87% rate of good pain control.4 This has traditionally been the main indication for DREZ lesioning, and most series for this indication note good pain relief in a majority of patients (usually between 50% and 80% of the cohort). The limited series of results of DREZ lesioning for phantom limb pain show less favorable outcomes (14%–67% good pain relief). Outcomes to these are similar for DREZ lesioning when used for pain caused by spinal cord injury and truncal postherpetic pain.8 It is worth noting that in spinal cord injury patients, DREZ myelotomy works only for “end-zone” pain and does not help with pain below the injury level.
Caudalis DREZ procedure was initially associated with a high incidence of postoperative ataxia (up to 90%) because of the location of the nucleus caudalis deep to the spinocerebellar tract. Nashold et al. developed new angled, insulated RF needles specifically for this procedure that protected this pathway from damage during lesioning of the nucleus caudalis, reducing the ataxia complication rate down to 39%.10 As opposed to spinal DREZ, the best indication for caudalis DREZ is postherpetic facial pain (71% excellent to good relief in the Duke series11). However, this procedure is rarely performed at this point. The main indication for nucleus caudalis DREZ, in the authors’ experience, is the trigeminal anesthesia dolorosa that develops following previous surgical interventions for treatment of trigeminal neuralgia.7
Resection of a peripheral nerve found its most significant use in the treatment of trigeminal neuralgia12–15 and painful peripheral neuromas.16,17 Although it is not often used for the former indication, it remains a mainstay of treatment for the latter.
Avulsion of the peripheral branches of the ophthalmic nerve (supraorbital and supratrochlear nerves) was often used in the treatment of trigeminal neuralgia in this region so as to selectively cause cutaneous anesthesia while avoiding the corneal anesthesia that often results from RF trigeminal gangliolysis aimed at the fibers of the first trigeminal nerve branch. This has also been applied to the branches of the maxillary and mandibular nerves in patients deemed inappropriate candidates for other procedures for relief of trigeminal pain.
Supraorbital neurectomy is most commonly performed via an incision through the eyebrow, while infraorbital neurectomy uses a transcutaneous approach with a small horizontal incision or transorally via the gingivolabial margin. After the nerve is located, it is wound around a small instrument and avulsed.
Grantham and Segerberg18 reported an average duration of pain relief from these procedures of 33.6 months. Oturai et al.19 compared RF coagulation and neurectomy and found that only 51% of patients undergoing neurectomy were pain free postoperatively and 78% had pain recurrence compared with a pain-free rate of 83% of the RF cohort, with only 49% pain recurrence.
Neurectomy has also been used for orbital pain,20 thoracic pain,21 shoulder pain,22 and pelvic pain.23–25 It is sometimes applied as a treatment of postherniorrhaphy pain seen in 5% to 8% of people undergoing hernia repair.26 Among the 26 patients with postherniorrhaphy pain reported by Zacest et al.,27 19 had significant initial pain improvement after ilioinguinal neurectomy, but 13 experienced recurrence of pain. Pappalardo et al.28 demonstrated that the long-term results for this procedure are not durable. The best results from the procedure seem to be reported either in only small series of patients29 or series with only limited follow-up time.30
Ganglionectomy is intended to avoid the issue of peripheral nerve regeneration, which may follow peripheral RF ablation or avulsion. Although selecting patients who will benefit most from the procedure remains a challenge, most investigators agree that diagnostic anesthetic nerve blocks of the prospective target root should produce significant temporary pain relief.
The dorsal root ganglion contains the cell bodies of the sensory neurons whose central projections enter the dorsal horn of the spinal cord. The ganglion itself lies in the lateral aspect of the neural foramen, distal to the termination of the subarachnoid space in the nerve root sleeve. It may be exposed by resection of the lateral portion of the facet joint and inferior aspect of the lamina of the superior vertebral segment overlying the target root. Opening the root sleeve exposes the ganglion, which can be separated from the underlying ventral root and resected.
The C2 ganglion (alone or with C3 ganglion) has been resected as a therapy for intractable occipital neuralgia. In this procedure, the C2 ganglion is located ventral to the prominent venous plexus in between the laminae of C1 and C2. The inferior aspect of the C1 lamina must sometimes be removed to gain access to the ganglion.
Results from ganglionectomy have been highly variable. In Taub et al.’s31 large series of 61 patients who underwent ganglionectomy for persistent radicular pain following lumbar surgery, 59% of patients achieved good pain relief. Strait and Hunter32 reported that 66% of their patients who had both the L5 and S1 ganglia resected for this same indication were pain free. However, of the 37 patients in Wetzel et al.’s33 series followed at least 2 years after ganglionectomy, only 19% of patients had durable pain relief from the procedure. North et al34 published even more disappointing results, with only 1 of the 13 patients reporting greater than 50% pain relief at 5.5 years postoperatively. There was little effect on medication intake and minimal functional improvement in the cohort.
Despite these issues, ganglionectomy may yet have a role to play. Young35 and Arbit et al.36 both published series of patients treated with ganglionectomy for cancer pain. In the latter series, 13 of 14 patients had excellent or good results following thoracic ganglion resection for malignant chest wall pain. However, the median follow-up period was only 22 weeks (longest, 45 weeks), which may provide one explanation for the greater utility of the procedure in cancer pain.
Acar et al.37 found that the procedure may also be useful for treatment of intractable occipital neuralgia in patients who received good temporary relief from selective C2 and C3 blocks. At final follow-up (mean, 42.5 months), 60% of patients reported either excellent or moderate pain relief. In Lozano et al.’s38 series, 80% of patients with neuropathic or posttraumatic occipital pain reported an excellent or good response to the procedure. Not surprisingly, individuals who had undergone peripheral neurectomy or RF ablation procedure before ganglionectomy did not obtain additional pain relief from the ganglionectomy.
Palmar hyperhidrosis is the most common contemporary indication for sympathectomy. However, interruption of the sympathetic chain has long been performed for treatment of a variety of pain syndromes, such as complex regional pain syndrome (CRPS, types I and II) and angina pectoris, as well as painful vasospastic disorders such as syndrome X and Raynaud’s syndrome.
The mechanisms by which the sympathetic nervous system either generates or maintains neuropathic pain syndromes are still not well understood despite significant research in this area.39,40 Conditions thought to have sympathetically mediated pain often have a pain distribution that does not conform to traditional peripheral nerve or dermatomal innervation patterns and whose intensity is out of proportion to the inciting event or imaging findings. Vascular and dystrophic changes often accompany the pain.
In determining a patient’s candidacy for sympathectomy, a determination must be made as to the relative contributions of sympathetically mediated pain and sympathetically independent pain the overall level of pain. Most commonly this is determined by observing the clinical response to local anesthetic sympathetic blocks. Intravenous phentolamine (α2-adrenergic blockade) and guanethidine Bier block (adrenergic depletion) may also be used to this end. Sympathectomy is offered to those patients with appropriate pain syndromes who have failed other therapies and have demonstrated substantial temporary relief from these injections.
Surgical sympathectomy may be performed via several routes, depending on the region of the chain to be disrupted. Thoracic sympathectomy is most commonly performed by resecting the T2 and T3 ganglia for the treatment of upper extremity pain. This region is approached either anteriorly via a small thoracotomy or, most typically, via thoracoscopic approaches. The sympathetic chain runs on the paramedian posterior thoracic wall. The chain is coagulated and sectioned above and below the intended ganglia, and the specimen is removed. Costotransversectomies at T2 and T3 may be performed to access the chain from a posterior approach. The chain is located over the pleura near the lateral vertebral body and may be clipped/coagulated and resected. The ganglia from T9 to T12 may be resected, along with the splanchnic nerves, for relief of neuropathic visceral pain (such as in chronic pancreatitis) that has responded temporarily to splanchnic blockade. This most frequently is performed as a bilateral procedure.
The ganglia at L2 and L3 may be resected for relief of pain in the lower extremities. These may be approached via an open, muscle-splitting retroperitoneal approach through a flank incision, sweeping the peritoneal sac away from the vena cava or aorta (depending on the side of symptoms). The chain is found at the junction of vertebral body and psoas muscle.
Wilkinson41 has pioneered RF thoracic sympathectomy. This involves fluoroscopically placing RF needlelike electrodes at the levels of the T2 and T3 sympathetic ganglia. The ganglion is located near the dorsal half of the vertebral body near the craniocaudal midpoint of the vertebral body. Multiple lesions are created in the craniocaudal direction to ensure appropriate lesioning. Intraprocedural monitoring of limb temperature may be used to determine the procedural endpoint. A 2°C rise in temperature in the ipsilateral limb is considered significant. Complications from thoracic procedures include pneumothorax, Horner’s syndrome, vascular injury, and intercostal neuralgia. Lumbar sympathectomy carries the risk of ejaculation problems in men. Rarely, patients may experience “postsympathectomy neuralgia,” a constant, aching pain in the proximal portion of the targeted limb. This is almost always self-limited to several months.
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