This review encompasses the most common spinal cord lesioning procedures used for the treatment of pain: dorsal root entry zone lesioning, open cordotomy, percutaneous cordotomy, and midline myelotomy. A literature review and summary of each technique regarding relevant anatomy, patient selection, surgical technique, outcomes, and complications are discussed. A general review of somatic and visceral pain pathways of the spinal cord is included, as each procedure requires an understanding of the advantages and disadvantages of various approaches to lesioning the spinal cord for pain. Neurosurgical education of these rarely used procedures needs to be included in residency and fellowship training.
Key points
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Dorsal root entry zone lesioning is excellent for brachial plexus avulsion pain (54%–91% pain relief), “end-zone” spinal cord injury pain, and inoperable upper thoracic tumors that compress the brachial plexus.
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Open cordotomy is excellent for unilateral lower extremity pain due to malignancies, such as sarcoma of the hip and legs. Poor results for chronic, nonmalignant pain (such as spinal cord injury–related pain).
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Percutaneous cordotomy is excellent for pain related to malignancy in the lower quadrant, including abdominal wall, pelvic bone, and lower extremity (such as carcinomas and sarcomas invading the lower quadrant).
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Patients with visceral pain due to abdominal or pelvic malignancies are ideal candidates for midline myelotomy.
Introduction: nature of the problem
The goal of this article was to summarize the relevant anatomy and physiology of pain transmission into the spinal cord through the dorsal root entry zone (DREZ) and subsequently in the spinal cord, and in using this knowledge, to select appropriate patients for appropriate lesioning of the DREZ or spinal cord in the treatment of a variety of pain syndromes. Furthermore, details regarding operative technique from the author’s experience should aid the reader in optimizing the outcomes and minimizing complications in appropriately selected patients for such procedures.
Clinical Anatomy of Pain Conduction in the Spinal Cord
Details regarding the anatomy and physiology of pain perception and transmission in the nervous system are discussed elsewhere in this text. The following section is a summary of the pertinent concepts when considering whether lesioning of the spinal cord would be appropriate in treating a painful condition. In our experience, the treatment of chronic pain is best optimized when the physician first understands the etiology of the pain and then arrives at an anatomic localization of the generator for the pain. Through understanding the exact character of the pain and its location, the surgeon can then make a thoughtful judgment as to whether the pain is, first of all, accessible, and second, where to make the lesion or pursue other forms of treatment, such as neuromodulation or pharmacotherapy. Furthermore, experienced surgeons then are able to weigh the accessibility of whether spinal cord lesions would have a reasonable chance of producing significant pain relief versus the potential complications that might be encountered with this procedure.
Spinal cord lesioning procedures are particularly suited for management of somatic pain , that is, painful sensation mediated through the spinothalamic tract. This is due to the discrete anatomy associated with pain mediated through the somatosensory pathways of the spinal cord. Although visceral pathways are also mediated through the spinal cord, alternate pathways through the autonomic nervous system and cranial nerves make it difficult to provide significant pain relief only through spinal cord–based procedures. Understanding the differences in the functional anatomy of these 2 types of pain is essential to success with patient selection and surgical outcomes.
Anatomy of pain pathways in the spinal cord
Several methods of classification of pain pathways in the spinal cord have been published. One classification process is based on the physiologic understanding of the modality of pain transmission, namely nociceptive versus non-nociceptive pain fibers. This classification distinguishes the pathways mediating pain generated by noxious stimuli (nociception) or non-noxious stimuli. This differentiation allows the surgeon to (1) differentiate whether transmission of painful sensation occurs primarily through somatic pain pathways mediated by the dorsal horn or whether alternate pain-enhancing pathways (for example mechanical or temperature sensitivity) are also involved, (2) whether appropriate medical therapy or other interventional therapy has been tried, and (3) what the potential prognosis for lesioning such pain pathways will be for a given patient. Fig. 1 illustrates the nociceptive and other pain pathways as they enter the DREZ on cross-section of the spinal cord. This anatomy holds true for cervical, thoracic, and lumbar segments, but with different proportions. Several anatomic features are worth noting from a surgical standpoint: (1) as fibers enter the dorsal horn, large fibers of proprioception are located medially, large myotactic fibers are located in the middle of the dorsal root, and smaller (C) fibers associated with nociception, autonomic function, and light touch are located on the lateral edge of the entry zone; (2) the Lissauer tract is located immediately lateral to the DREZ and is responsible for longitudinal transmission of nociceptive information at least 2 segments superior and inferior to the point of entry into the cord; (3) the corticospinal tract, responsible for voluntary control motor function, is located in the white matter immediately lateral to the DREZ and dorsal to the dentate ligament; and (4) most nociceptive and other small diameter fibers synapse within Rexed lamina I to V of the dorsal horn of the spinal cord.
The lateral spinothalamic tract (STT) is the primary conductor of nociceptive information to the contralateral thalamus. Although the second-order neurons are mostly located in the dorsal horn of the cord, most projections of these neurons cross the midline just anterior to the central canal and then collect in the white matter tract of the SST located near the anterior, lateral spinal cord surface ( Fig. 2 ). Understanding the exact location of where lesions should be performed depends on whether interruption of somatic pain pathways needs to be limited to a unilateral extremity or bilaterally.
Transmission of nociceptive information crosses the midline in the anterior commissure, and therefore represents a location by which bilateral conduction of painful sensation can be addressed in a single location in the spinal cord (see Figs. 1 and 2 ). The anterior commissure of the spinal cord is located just anterior to the central canal, deep within the interior of the spinal cord. Within a few millimeters and abutting the anterior surface of the spinal cord is the anterior spinal artery, an important anatomic landmark to respect when making lesions in the anterior spinal cord region.
Some additional anatomic concepts are unique to each lesioning procedure and worth mentioning next.
Unilateral limb pain and the DREZ
Success with DREZ lesioning is typically thought of for unilateral limb pain. Although bilateral DREZ procedures can be performed successfully, the anatomic concepts relate to pathology of the first-order neuron due to either deafferentation or miscommunication of nociceptive information in each DREZ as a separate pathologic entity. For conceptual simplicity, DREZ lesioning can be thought of as a treatment for pain that is believed to be confined to a unilateral limb. Understanding how and where pain is mediated on immediate entry into the dorsal aspect of the spinal cord helps the surgeon to know exactly how to place the lesion precisely with the most efficacy and least morbidity.
The arrival of nociceptive information into the spinal cord splits and either synapses in the dorsal horn (Rexed lamina I to V) or projects along the longitudinal axis of the spinal cord via the Lissauer tract. The Lissauer tract is a key pathway that conducts nociceptive information at least 2 segments above and below the DREZ (see Fig. 2 A). Through this tract, the first-order neurons synapse with multiple segments of the spinal cord and distribute nociceptive information to nearby somatic zones that are involved in reflexive behavior. However, it blurs the margin of nociceptive information, leading to a less distinct border of a painful zone described by the patient. It is important, thus, for surgeons who contemplate the extent of DREZ lesioning to understand that up to 2 segments above and below a specific dermatomal segment may be involved in nociceptive transmission.
Another important anatomic concept to keep in mind is the relationship of the dorsal horn to adjacent white matter tracts ( Fig. 3 ), and that these dimensions change throughout the spinal cord. The following are important concepts: (1) the angle of the dorsal horn with respect to the sagittal axis is greater in the cervical enlargement (35° ) of the cord than in the lumbar-sacral enlargement (approximately 20°); (2) lateral to the dorsal horn is the corticospinal tract organized somatopically, with cervical, thoracic, and lumbar fibers arranged in a medial-to-lateral direction; and (3) the dorsal columns that are medial to the dorsal horn are organized with converse somatotopy, namely cervical proprioceptive fibers are lateral to lower extremity fibers. These relationships mean the following to the surgeon contemplating a lesion of the DREZ. If dorsal root fibers are avulsed, as commonly seen in pain associated with brachial or lumbar-sacral plexus trauma, then deviating laterally from the DREZ may result in ipsilateral hemiparesis below the level of the lesion. Alternatively, if lesions deviate too medially from the DREZ, loss of proprioception may occur. These risks should be included in the consideration of this procedure.
Unilateral limb/truncal pain and cordotomy
The advantage to lesioning the STT by cordotomy is to address the collective transmission of nociception entirely below the level of the lesion. Cordotomy is most useful in addressing malignant pain; however, success for other types of nonmalignant pain also has been reported. Consequently, the surgeon needs to decide whether the pain involves more than a specific region of the plexus in a limb. For example, although DREZ lesioning may address severe pain in the upper extremity (whether due to trauma or cancer) as high as the shoulder area, a cordotomy performed in the contralateral upper cervical STT will create significant numbness and dysesthesia in the arm and entire trunk and leg. This may be the desired outcome in a patient with cancer of the upper limb and trunk, but not in someone with a brachial plexus avulsion. In general, patients who experience severe pain that originates from cancer involving the pelvis, leg, hip, and lower trunk are ideal candidates for a cordotomy procedure (whether open or percutaneous) .
The relevant anatomy to performing an open or percutaneous cordotomy lies in understanding the discrete somatotopy of the STT as it ascends the spinal cord. Several important concepts are evident:
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The STT lies just anterior to the dentate ligament and near the anterolateral surface of the cord.
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The anterior spinal artery is a significant vascular structure whose midline position must be appreciated and avoided during open transection of the STT.
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The corticospinal tract lies dorsal to the dentate ligament and should not be injured by either approach to the anterior half of the cord.
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The sacral fibers lie closest to the surface and posterior in the STT, followed by lumbar, thoracic, and cervical fibers located progressively more anterior and deeply.
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The levels of adequate pain control are several levels below the lesion; C1/2 percutaneous cordotomy can reach as high as C5, a T4 open cordotomy will result in T10 analgesia.
These concepts are used to identify the location of the STT in the cervical region by either injecting contrast or performing high-resolution computed tomography (CT) scans to locate the dentate ligament and subsequently define the anterior quadrant of the intended lesion. It is imperative to know that the lesion is made anterior to the dentate ligament so as to avoid damaging the corticospinal tract. Also, the lower extremity pain fibers are located more closely to the dentate ligament and superficially. Hence, when performing awake test stimulation before radiofrequency lesioning of the cervical STT, insertion of the lesioning electrode just anterior to the dentate ligament will first produce paresthesia in the contralateral lower extremity first and advances rostral as the electrode is inserted deeper and more anterior into the STT.
Percutaneous cordotomy procedures are performed at the C1/2 interspace typically due to the ease of access to the anterior half of the spinal cord through a direct lateral approach with image guidance. However, the anatomy must be visualized through either contrast injection with fluoroscopic guidance or CT guidance. Test stimuli confirm the location of the STT to the surgeon, and therefore the patient needs to be awake at least for this confirmatory test before lesioning. Other critical anatomic structures are nearby in the upper cervical region that can create serious or fatal complications, including respiratory interneurons near the intermediate gray matter, cardiovascular and sympathetic tracts, and the vertebral artery and its branches. Nonetheless, many neurosurgeons have learned this anatomy well and the overall complication rates for experienced surgeons performing cordotomies was well under 5% in large series.
Open cordotomy requires being aware of additional anatomic structures that may be encountered while creating the anterolateral quadrant lesion. In particular, the lesion will usually extend medially into the interior of the gray matter and then anterior to encompass the spinocerebellar tracts. Sectioning the anterior gray matter will result in segmental loss of motor neuron innervation, which is well tolerated in the thoracic region but not in the cervical region.
Special attention must be given to any bilateral high cervical lesions for pain because of the presence of the respiratory drive neurons located immediately medial to the lateral spinothalamic tract ( Fig. 4 ). Although unilateral lesions at C1/2 are well tolerated and associated with a low frequency of respiratory complications, bilateral high cervical cordotomy lesions escalate the risk for respiratory complications significantly.
Abdominal/pelvic and bilateral lower extremity pain and midline myelotomy
The term midline myelotomy has evolved to encompass a midline lesion that may or may not involve the anterior commissure. Consequently, for discussion sake, commissurotomy will be used to discuss lesions involving the anterior commissure, and limited midline myelotomy will be used to discuss lesions involving just the dorsal columns.
Complete midline myelotomy (commissurotomy) is an attractive alternative to bilateral cordotomy because it addresses bilateral nociceptive pathways through a single midline incision (see Fig. 1 ). Projection of dorsal horn neurons to the contralateral spinothalamic tract cross anterior to the spinal canal either within the same segment or obliquely across several segments. Therefore, disruption of the anterior commissure should extend at least 2 to 3 levels surrounding the primary segmental level mediating the pain. For abdominal and pelvic pain, this would include the spinal cord segments from T10 to the conus. When dividing the commissure from a posterior approach through the midline, it is necessary to divide the dorsal columns and should be done as close to the midline as possible so as to minimize deficits associated with loss of proprioception from dorsal column damage.
Neurosurgeons discovered that visceral pain relief was excellent in these patients in addition to the intended bilateral somatic pain reduction. Some, like Mansuy and colleagues, noted this effect despite poor coverage of the anterior commissure. Speculation began to emerge discussing the existence of a dorsal column visceral pain pathway. Willis and colleagues eventually described the anatomic existence of a visceral pain pathway in the deep midline of the dorsal columns in animals, leading to the notion that interruption of this pathway alone would have an effect on visceral pain. A limited midline myelotomy that just lesions the dorsal columns and avoids cutting the anterior commissure was then described by Gildenberg and Hirshberg in 1981 and then further reduced to a small transverse lesion by Nauta and colleagues in 1997. This limited lesion only interrupts ascending pathways in the dorsal columns thought to mediate visceral pain. A nice personal perspective on the evolution of midline myelotomy procedures is provided by Gildenberg himself in 2001.
Furthermore, on reaching the anterior sulcus of the cord, the commissure is divided and care must be exercised to avoid damaging the anterior spinal artery, which lies a few millimeters anterior.
Selection and Workup of Patients
Patients who are being considered for surgical lesioning for the treatment of pain, in general, should have failed more conservative management with medications. However, in cases of severe, debilitating pain that is poorly responsive to opioids or other forms of localized pain medication delivery (eg, neurolytic blocks), lesioning represents a highly effective neurosurgical therapy that returns significant quality of life to the patient. Ideally, the candidate who benefits most from a lesioning procedure versus medical management has pain that is well localized to an accessible anatomic pathway for neurosurgical ablation or lesion . Hence, understanding the spinal cord pathways of pain transmission, discussed previously, is requisite to proper patient selection and a desirable outcome. Many patients with severe pain related to cancer or trauma are willing to accept sensory deficits in exchange for significant pain relief; however, the skill of a neurosurgeon who selects a lesioning procedure for pain control is most evident when the loss of function is minimized as well as the pain. The following discussion reflects general principles and examples of appropriate patient selection for the 3 spinal cord lesioning procedures reviewed in this article: DREZ lesion, STT lesion (cordotomy), and midline myelotomy (commissurotomy).
Unilateral limb and plexus pain
Pain described in a unilateral limb or suggesting confinement to the plexus usually is best suited for DREZ lesioning. The pain needs to be primarily localized to the first-order neuron or the entry zone of the cord. Three types of patients are ideal candidates to consider for DREZ lesioning: traumatic brachial plexus injury, patients with segmental pain at the level of their spinal cord injury, and apical thoracic tumors (Pancoast tumor). Additional details for each kind of patient are given in multiple other reviews. However, the following are usually consistent findings that indicate candidacy for DREZ:
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Prickly or electric, shooting pain limited to the region of the plexus; or
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Partial or complete loss of sensation in the affected limb that may or may not be associated with motor loss in the same limb due to trauma; or
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Presence of pseudomeningocele seen on magnetic resonance imaging (MRI) or myelography of the affected spinal cord region associated with the trauma; or
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Presence of compressive lesion in the thoracic apex in proximity to or involving the inferior brachial plexus region; or
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Hyperpathia of the zone of transition between normal sensation and loss of sensation associated with spinal cord injury.
Findings that would indicate poor outcomes with DREZ include the following:
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Constant burning pain in the limb; or
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Presence of herpetic neuropathy; or
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Pain that extends outside the region of the limb, such as the shoulder, trunk, or pelvis; or
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Burning pain in the lower extremities that is well below the level of a spinal cord injury.
The anatomy of the spine as well as spinal cord should be known in patients before recommending a DREZ procedure. Typically an MRI or myelogram/CT of the region should be obtained to review spinal cord anatomy as well as bony defects that may be associated with previous surgeries or injury. Other extrinsic factors that contribute to the pain should be ruled out. Patients who describe pain that is worse with mechanical movement, slowly progressive sensory or motor deficits, “electric, shocklike” sensation with movement, or Lhermitte phenomenon have noncharacteristic neuropathic pain complaints. A thorough workup before offering a DREZ lesion would include determining the presence of mechanical instability, syringomyelia, compressive lesions (such as a herniated disc, hypertrophied ligamentum flavum, or arachnoid cyst), or arachnoiditis. Even if the history suggests central neuropathic pain (burning, deep, steady pain at or below the level of the injury), an MRI of the affected region of the spine routinely obtained before surgery may prepare the surgeon for distorted anatomy that may be encountered with the planned exposure.
Unilateral lower quadrant pain
When pain extends beyond the leg and involves the hemipelvis and lower abdominal quadrant, a cordotomy is an excellent choice for surgical pain management. These patients are typically patients with cancer who have musculoskeletal involvement of the pelvis, hip joint, or thigh that creates pain well beyond the location of the lower extremity. Many times these patients have exhausted opioid analgesics, localized blocks or injections, or mechanical bracing. The neurosurgeon can make a significant impact on the comfort of these patients who are typically in the terminal phases of their disease with limited life expectancy.
Patients who have nonmalignant pain syndromes are not ideal candidates for either open or percutaneous cordotomy because of the recurrence rate of pain within a few years or the emergence of new central neuropathic pain (burning dysesthesias below the level of the lesion). Patients with truncal herpetic neuropathy or lower extremity central neuropathic pain due to spinal cord injury, for instance, are better suited for more long-term neuromodulation therapies, such as intrathecal drug therapy or perhaps a neurostimulator implant (discussed elsewhere in this text).
Bilateral lower extremity pain or lower abdominal/pelvic pain
In patients with bilateral lower extremity pain and, in particular, with involvement of the pelvis and lower abdominal organs, a single lesion disconnecting the anterior commissure through a lower thoracic approach has been quite effective in relieving severe refractory pain. The typical patient is one with pelvic cancer or sarcoma that invades bilateral structures in the pelvis and lower extremities. These patients can undergo a myelotomy with significant preservation of motor function, but may have reduced or lost bowel and bladder function. The lesion is elegant and effective in this population of patients and the loss of proprioception and potential bowel and bladder control may be acceptable to these patients who are otherwise bedridden with severe pain.
Most cases discussed for midline myelotomy are for patients with lower abdominal, pelvic, and lower extremity pain. However, patients who experience severe abdominal or pelvic pain due to malignancy appear to be ideal candidates for a limited division of only the dorsal columns so as to lesion the visceral pain pathways without interruption of the anterior commissure. Some patients with celiac region pain, associated with gastric or pancreatic cancer for example, undergo a limited high thoracic myelotomy with reasonably good outcomes. Uterine and colorectal cancer pain also has been relieved by a limited dorsal myelotomy. However, there is little literature discussing the value of this technique for thoracic cancer or mediastinal disease causing severe pain. The risks of respiratory and sympathetic damage (fibers located near the central gray matter) in creating a mid to upper cervical midline myelotomy are likely the reasons why this technique has not been used much for upper trunk and arm pain.
Surgical Technique
In general, one first must understand how many levels in particular should be involved in the lesion. Fig. 5 illustrates the relationship between spinal nerve roots and vertebral levels. For DREZ lesioning, lesioning should encompass at least 2 levels above and below the involved segments. For cordotomy, effective analgesia occurs 3 to 4 levels contralateral to the lesion site. The same is true for midline myelotomy, namely the effect of the analgesia essentially begins 3 to 4 levels caudal to the lesioning site. Consequently, it is difficult to obtain adequate analgesia even with a C1 to percutaneous cordotomy above the level of C5.
Preoperative measures
Preoperative MRI or myelography and postmyelography CT scan can provide essential anatomic details regarding pseudomeningoceles, adhesions of the spinal cord, distorted spinal cord anatomy, or spinal deformities. The value of such studies for each group of patients was highlighted previously. Steroids are commonly given at the beginning of the procedure to reduce postoperative spinal cord edema (eg, dexamethasone 6–10 mg intravenously [IV] every 6 hours tapered over a few days).
Approach laminectomy and durotomy for open procedures
Patients are positioned prone, under general anesthesia, and usually on a radiolucent table for fluoroscopic confirmation of vertebral levels. A hemilaminectomy that is performed for unilateral DREZ or open cordotomy lesions may reduce the likelihood of postlaminectomy kyphosis. This approach is appropriate for most cases in which no previous laminectomy has been performed; yet, it is much wiser to perform a standard laminectomy when intradural adhesions, syringomyelia, or distorted spinal cord anatomy are seen on preoperative imaging. For a unilateral DREZ or open cordotomy lesions, one can perform a hemilaminectomy with a high-speed drill exposing the dorsolateral spinal canal. For a bilateral DREZ lesion, a more standard laminectomy can be performed. The end result of the exposure needs to ensure that the appropriate spinal cord segments are exposed with an adequate opening to allow the dura to be reflected and the spinal cord visualized. Although the spinal cord segments align with vertebral segments in the cervical spine, inferiorly in the spine this relationship becomes discordant, and surgeons must make adjustments, as seen in Fig. 5 .
If significant spinal cord injury has occurred, or if a midline myelotomy is planned, it is advisable to perform a bilateral laminectomy to ensure a view of both normal and abnormal anatomy. Use of the operating microscope with moderate to high-powered magnification is essential. Orientation of the midline, dorsal columns, vascular structures, dorsal rootlets, and dentate ligament all provide the neurosurgeon with appropriate entry landmarks and estimates of the location of the dorsal horn and corticospinal tract. If the dura and arachnoid are opened separately, blood from decompression of the dura can be removed and controlled before it enters the subarachnoid space, reducing the potential for postoperative adhesions. Once the arachnoid is opened, an assistant who can continue to aspirate blood and cerebrospinal fluid (CSF) from the field is very helpful because it allows the neurosurgeon to maintain attention on the exact location and extent of the lesion as it occurs.
Closure of the arachnoid and dura can be accomplished in 1 layer with a fine suture (4-0 or 5-0). The use of dural sealants, such as thrombogenic derivatives (eg, Tisseel; Baxter, Deerfield, IL) or synthetic derivatives (eg, DuraSeal; Confluent Surgical, Waltham, MA) may reduce the incidence of CSF leak. Fascia and cutaneous closure are performed in routine fashion.
Postoperative care
Patients are typically observed closely in the intensive care unit for the first 24 hours for any new neurologic deficits, such as mild weakness or diminished proprioception inferior to the lesion. If new postoperative deficits emerge, urgent imaging with MRI or CT myelography is appropriate to rule out hematoma or other anatomic complications. Most patients, however, can be mobilized by the first postoperative day after an open cord lesioning procedure. To reduce likelihood for CSF leak, patients who underwent cervical or upper thoracic lesions are instructed to keep the head of the bed elevated at least 30°, whereas those who underwent thoracolumbar exposures are kept flat for 24 hours. Most patients are encourage to get out of bed by the first postoperative day and encouraged to mobilize. Dexamethasone in tapering amounts is usually administered over the course of several days, but may be prolonged if new deficits are encountered that may result from edema secondary to the lesion. Patients are mobilized typically on the first postoperative day. Pain management is converted from IV to oral medications in anticipation of discharge within 3 days postoperatively. Most patients who benefit from cord lesioning will notice significant pain reduction by the second postoperative day, and may require very little pain medication at the time of discharge.
Even though close attention is paid to reducing risk from intradural spinal cord surgery, complications, such as bowel and bladder dysfunction, CSF leak, infection, and hematoma formation, are rare. These complications are typical of surgery related to exposure of the spinal cord and closure of the wound. In addition, postlaminectomy kyphosis is more likely to occur in patients with multiple-level laminectomies that extend laterally into the facet joint or pars interarticularis and in patients with significant preexisting spondylosis.
The following discussion is divided into each specific surgical technique for DREZ, cordotomy, and myelotomy.
DREZ Lesioning
The goal of DREZ lesioning is to create a selective destruction of neurons and fibers that enter the dorsal root entry zone. In 1979, Nashold and coworkers first described DREZ microcoagulation for brachial plexus avulsion pain and soon thereafter for other conditions, such as spinal cord injury. Fig. 6 illustrates the typical findings of a spinal cord injury in the lumbar region and the associated loss of innervation by the sensory rootlets in the dorsal part of the spinal cord. This figure illustrates the complexity of the anatomy typically involved in root avulsion and pain. Notice that the DREZ lesions follow along the dorsal lateral sulcus and an imaginary line from the T12 nerve root to the L2 nerve root seemed more caudally. Care should be taken to insert the DREZ electrode just lateral to the entry of the nerve root to be most effective in producing a lesion for both the segmental level of pain fibers as well as capturing the Lissauer tract. In this particular patient, who had spinal cord injury, the pain was most noticeable in the L3 to 4 region of the thigh. Hence, the lesions are started just at the T12 nerve root level and extend caudal to the level of the injury below.
Fig. 5 illustrates the relationship of spinal nerve roots with vertebral segments. Notice that for the typical brachial plexus DREZ lesion, an exposure of the dorsal spinal cord from C4 to T1 will allow a view of the related dorsal roots (C5–T1). For DREZ lesioning of the lower spinal cord related to spinal cord injury, it is advisable to expose at least 2 vertebral segments above the superior aspect of the painful zone. Typically, a bilateral laminectomy from T10 to L2 is performed for treatment of pain related to conus medullaris and cauda equina lesions.
Lesion location and technique
Fig. 7 shows the typical Nashold DREZ lesioning electrode and dimensions. Piercing the pia usually requires a sharp push, so as to minimize the deformation of the cord and minimize unwanted injury. The ideal location for the lesion should be at the lateral edge of the spinal rootlet as it enters the cord, where the nociceptive fibers are gathered (see preceding discussion of Clinical Anatomy of Pain Conduction in the Spinal Cord). The electrode should be inserted to the full depth of the exposed tip (2 mm), and in so doing, impedance measurements can be made to identify zones of injury. Nashold and colleagues described low impedance values (approximately 500–1000 Ω) associated with areas of injury, versus 1200 to 2000 Ω for normal gray and white matter of the spinal cord, respectively. This may be useful in delineating the DREZ area and avoiding deviating into adjacent spinal tracts. Somatosensory evoked potentials and motor evoked potentials may also aid in the identification of these adjacent tracts when there is significant anatomic distortion from previous injury. For cervical regions, the angle of the electrode is approximately 30° from midline, whereas in the lower thoracic region it is approximately 20°. The weight of the lesioning electrode is usually adequate to hold the electrode still without inadvertent dislodgement or movement during the brief lesion.
Lesions are made with the radiofrequency generator set to 75°C for 15 to 20 seconds. This usually results in a 1 × 2-mm lesion. The lesion is repeated down the length of the DREZ spaced approximately 1.0 to 1.5 mm apart, or essentially the width of the insulated end of the electrode. A typical unilateral DREZ procedure may result in a total of 40 to 60 lesions spanning 4 or more spinal cord segments. Thus, an efficient DREZ lesioning technique requires a coordinated effort among the neurosurgeon, the surgical assistant, and the individual running the lesion generator. Once a lesion is created, a small tan discolored area is left or a small puncture is seen where the needle penetrated the cord (see Fig. 6 ). It is important to continually reevaluate that DREZ lesions are following the dorsal lateral sulcus if no dorsal rootlets are seen. Once lesioning starts, staying focused on the orientation and direction of the DREZ minimizes deviation from the intended zone for lesioning, and the location of the previous lesion is not lost.
If avulsed rootlets are seen throughout the intended lesioning zone, the neurosurgeon may find it useful to begin rostral or caudal to the avulsed segments in the region containing spinal rootlets to identify the dorsolateral sulcus and progress into the avulsed region. Finally, it is unusual to see significant arteries cross the dorsolateral sulcus, as it is a watershed zone between the dorsal spinal arteries and the anterior spinal artery. However, a prudent neurosurgeon should always avoid injuring any significant arterial supply to the spinal cord.
The DREZ lesions are completed when either the lesions encompass 1 or 2 spinal cord segments above the painful zone or the impedances of the cord have normalized.
Complications for DREZ
Several reviews have been published regarding complications and outcomes of the DREZ procedure for RFL, laser, and microcoagulation. Table 1 summarizes the potential complications associated with radiofrequency DREZ lesioning for spinal cord procedures. In general, the most serious complications are usually associated with lesions that inadvertently are placed too far laterally and injure the corticospinal tract, resulting in permanent ipsilateral weakness below the lesion. This occurred in 3% to 14% of patients reported since 1990. It is most frequent with thoracic DREZ lesions where the dorsal horn is the thinnest and the margin for error is the least. Permanent sensory loss, namely ipsilateral loss of proprioception and light touch below the DREZ site, is tolerated better by patients, but is reported at a higher rate (2%–70% in reports since 1990). It appears that the smaller electrode and experience with the technique has resulted in a lower complication rate.
| Author, Year | Reason for DREZ | No. Patients | Permanent Sensory or Motor Loss | Transient Motor or Sensory Loss | Other, % |
|---|---|---|---|---|---|
| Samii & Moringlane, 1984 | BP, SCI | 35 | 0 | 3% M, 25% M, 23% both | 0 |
| Richter & Seitz, 1984 | BP, SCI | 10 | 30% S, 10% both | 10% M | 20 |
| Thomas & Jones, 1984 | BP | 34 | 12% M/S | 50% M/S | |
| Garcia-March et al, 1987 | BP | 11 | 9% M | ||
| Friedman & Bullitt, 1988 | BP | 39 | 60% M/S | ||
| SCI | 56 | 5% M, 5% minor | 16 | ||
| PHN | 32 | 69% M | |||
| Campbell et al, 1988 | BP | 10 | 20% hyperreflexia | 10 | |
| Ishijima et al, 1988 | BP, SCI, PHN | 30 | 62% S | 14 | |
| Saris et al, 1988 | Post-amputation | 22 | 41% mild M/S | 1 | |
| Saris et al, 1988 | Peripheral | 12 | >50% S, 8% M | 17% M, 8% sphincter, 74% mild dysmetria | 7 |
| Young, 1990 | Various – l g electrode | 21 | 24% S, 19% M, 5% both | ||
| Various – sm electrode | 37 | 3% S, 5% M | 1 | ||
| Kumagai et al, 1992 | Various | 17 | 71% S, 41% M | 35 | |
| Edgar et al, 1993 | SCI | 102 | 2% S, 3% M | 5 | |
| Sampson et al, 1995 | Conus | 29 | 3% S, 14% M, 10% sphincter | 3% M | 7 |
| Cauda equina | 10 | 10% M | |||
| Rath et al, 1997 | Various | 73 | |||
| Samii et al, 2001 | BP | 47 | 4% M | 10% M | 2 |
| Falci et al, 2002 | SCI | 41 | 70% S, 14% M | 9 | |
| Tomas & Haninec, 2005 | BP | 21 | 14% S/M | ||
| Chen & Tu, 2006 | BP | 60 | 25% S | ||
| Awad et al, 2013 | BP, SCI, Cancer | 19 | 11% M |
Prognosis of pain relief
Table 2 summarizes a review of the literature reporting outcomes in 10 or more patients undergoing radiofrequency DREZ lesioning for various neuropathic conditions other than postamputation pain. Very few reports on the outcome for postamputation pain exist and these results from small studies of radiofrequency DREZ lesioning are also included.
| Author, Year | No. Patients | Good Results (%) | Follow-up Period, mo |
|---|---|---|---|
| Brachial Plexus Avulsion Pain | |||
| Thomas & Jones, 1984 | 34 | 21 (62) | 4–44 |
| Samii & Moringlane, 1984 | 22 | 20 (91) | |
| Garcia-March et al, 1987 | 11 | 6 (54) | 8–58 (mean, 17) |
| Campbell et al, 1988 | 10 | 8 (80) | 7–52 |
| Ishijima et al, 1988 | 17 | 14 (82) | 6–57 |
| Young, 1990 | 18 | 13 (72) | |
| Freidman et al, 1990 | 56 | 33 (59) | 12–156 |
| Samii et al, 2001 | 47 | 30 (64) | 24–216 (mean 168) |
| Tomas & Haninec, 2005 | 21 | 13 (62) | 4–96 |
| Chen & Tu, 2006 | 40 | 32 (80) | 36–120 |
| Awad et al, 2013 | 10 | 6 (60) | 2–144 (mean 78) |
| SCI Pain | |||
| Weigand & Winkelmuller, 1985 | 20 | 10 (50) | 1–28 |
| Friedman & Nashold, 1986 | 31 | 23 (78) – end-zone pain | 6–72 |
| 25 | 5 (20) – diffuse pain | 6–72 | |
| Young, 1990 | 14 | 8 (57) | |
| Edgar et al, 1993 | 46 | 42 (92) | 2–96 (mean, 44) |
| Sampson et al, 1995 | 39 | 21 (54) | (mean 36) |
| Falci et al, 2002 | 41 | 33 (80) | 12–72 |
| Awad et al, 2013 | 6 | 5 (83) | 6–60 (mean 24) |
| Postherpetic Pain | |||
| Friedman & Bullitt, 1988 | 32 | 8 (25) | 6–72 |
| Young, 1990 | 11 | 6 (54) | |
| Phantom-limb Pain | |||
| Weigand & Winkelmuller, 1985 | 7 | 1 (14) | 1–28 |
| Saris et al, 1988 | 9 | 6 (67) | 6–60 |
Overall, the success of radiofrequency DREZ lesioning has improved over the years. It continues to remain true that the best results are obtained with patients who have brachial plexus avulsion. Patients can expect good to excellent reduction in brachial plexus avulsion pain 54% to 91% of the time, and it appears to last in at least 50% of patients over 5 years. Patients who had end-zone pain rather than diffuse distal pain related to spinal cord injury (SCI) had better outcomes (78% vs 20%). Although follow-up studies for SCI pain are not nearly as long, the results also appear to hold for more than 3 years. Both Tomas and Haninec and Falci and colleagues indicated that intraoperative electrophysiology of the dorsal horn during these procedures is likely to enhance the outcomes and reduce complications. Both of these groups suggest that tailoring the lesioning procedure to include areas of hyperactivity in the DREZ region will capture additional levels mediating pain not normally anticipated in the preoperative plan. Patients on the other hand who have a “dull, aching, burning pain” distal to the region of spinal cord injury are similar to those who complain of phantom-limb stump pain, and less optimal results are seen. These data suggest that lesioning of the DREZ will not encompass the pain pathways mediating this type of pain. In fact, autonomic pathways extrinsic to the spinal cord may mediate the refractory portions of the pain not treated by DREZ lesioning.
DREZ lesioning for postherpetic neuralgia pain is associated with poor outcomes and increased morbidity. Although initial pain relief was seen in 29 of 32 patients in the first several months, Friedman and Bullitt found that only 8 of these patients had good pain relief by a year. Considering the increased risk for motor deficits following thoracic DREZ lesioning (see Table 1 ), one should be cautious in offering good results in the long run in patients with this type of pain.
Laser or microsurgical DREZotomy lesioning has been extensively described by Sindou since 1972. When others have compared the results with radiofrequency lesions, similar results were found in a few reports. The advantage of radiofrequency lesioning is that the lesions are usually approximately 1 mm round and are highly reproducible. Furthermore, insertion of the Nashold DREZ electrode will ensure a lesion depth of 2.5 mm with equal spacing around the electrode tip (see Figs. 6 and 7 ). Stimulation can easily be performed just before each lesion in areas in which the anatomy is obscure. These are advantageous over an open lesioning technique of the DREZ in which the spinal cord is visually disrupted. A disadvantage of the radiofrequency technique is the lack of visualization of the actual lesion within the spinal cord. There may be skip areas when lesions are not spaced tightly, which may result in less optimal outcomes and potential for increased morbidity due to wandering from the DREZ line.
Summary for DREZ
Radiofrequency DREZ lesioning is an excellent procedure to offer patients with medically refractory pain due to a variety of syndromes. In particular, patients with pain due to brachial plexus avulsion and end-zone pain related to traumatic spinal cord injury are to be considered for this procedure. The neurosurgeon contemplating this procedure should have a solid understanding of the microanatomy in the DREZ region of the spinal cord and be familiar with contemporary intraoperative physiologic testing to optimize the outcomes from this surgical procedure.
Open Cordotomy
Initial description of the open cordotomy procedure for severe debilitating pain was written by Spiller and Martin in 1912. It was in fact the most common surgical procedure for pain in the early part of the twentieth century. Since then, the surgical procedure has not changed significantly. Exposure of the spinal cord for open cordotomy involves being able to adequately visualize and manipulate the lateral aspect of the spinal cord via the dentate ligament.
Lesioning technique
For unilateral cordotomy, a hemilaminectomy exposing the spinal canal from the midline to the facet joint is necessary. A durotomy was then made so as to easily visualize the dentate ligament and allow pop rotation of the spinal cord posteriorly. Once the dentate ligament is identified, it is disconnected from the dura and gently elevated, revealing the anterolateral part of the spinal cord ( Fig. 8 ).
An improvised cordotomy instrument was created by snapping a Weck blade to a length of 4 to 8 mm and placing it at a right angle in Ryder forceps. The blade was inserted to a depth of 3 to 4 mm just underneath the dentate ligament and swept anteriorly. An angled microdissector was then used to reinforce the lesion by sweeping the instrument in the subpial space to ensure complete transection of the anterolateral spinal cord. Minimal bleeding would sometimes ensue, and this could typically be managed with conventional hemostatic techniques. Closure of the spinal cord dura and superficial layers is performed with the goal of reducing likelihood of spinal fluid leak.
Cordotomy can be expected to create a lesion with adequate analgesia several segments below on the contralateral side. For example, it is not uncommon to find a loss of pain and temperature below T8 after technically adequate open cordotomy at T4 to 5. This usually is sufficient to provide significant relief of lower quadrant pain that includes the pelvis, hip, thigh, and lower limb contralateral to the lesion. In patients with bilateral leg pain and pelvic pain (for instance, a patient with osteosarcoma involving both hips), bilateral cordotomy has been successful. Table 3 provides a list of investigators who report on the technique and outcomes of open cordotomy. Although the literature contains few reports of large case series, this technique is still performed at selected medical centers in the treatment of cancer pain.
| Author, Year | No. Patients | Lesion Level | Good Results | Complications | Follow-up Period (mo) |
|---|---|---|---|---|---|
| Cowie & Hitchcock, 1982 | 43 Cancer pain 13 Nonmalignant | C, T | 93% immediate 55% at 1 y | Transient urinary retention (11%) Transient hemiparesis (3.5%) Permanent dysesthesia (7%) Death from respiratory failure – cervical (3.5%) | <18 |
| Piscol, 1975 | C, T | Cancer: 65% long term Chronic pain: 20%–63% long term | >12 | ||
| Tomycz et al et al, 2014 | 4 Cancer pain 5 Nonmalignant | T | 33% good 33% some improved | Mirror pain/dysesthesia (11%) Transient leg weakness (22%) Urinary incontinence (33%) | 2–72 (31 median) |
| White et al, 1950 White & Sweet, 1969 | 145 Cancer pain 65 Nonmalignant | C | 54% longer than 1 y | Urinary incontinence (13%) Leg weakness (5%) Mortality (4%–20%) | 2–132 |
| T | 77% by 6 mo 56% longer than 1 y |
Complications of open cordotomy
Table 3 includes a summary of complications seen with open cordotomy. The 2 most common complications are urinary retention or incontinence (11%–33%), permanent dysesthesias that may be bothersome (7%–11%), transient hemiparesis (3.5%–22%), and respiratory distress or suppression in cervical cordotomies (3.5%–4%). Mirror pain also has been an unusual complication of open thoracic cordotomies in patients with cancer (7%–11%) in which a similar pain is experienced in the opposite side of the original painful region within weeks to months after the cordotomy.
Other complications that are shared with open dural procedures and laminectomies include possible mechanical spinal instability, CSF leak, and meningitis.
Prognosis of pain relief
Few long-term studies (longer than 2 years) exist for open cordotomy for cancer pain, likely because of short-term survival of the patient population usually indicated for this procedure. However, the best follow-up appears in reviews by White and colleagues, Cowie and Hitchcock and Piscol. This is summarized in Table 3 . A few facts need to be understood about the long-term prognosis of this procedure. More than half (77% reported by White and Sweet ) of the patients typically will have total immediate relief from their cancer pain, and one-fourth will have partial relief. However, the remaining patients may experience no benefit and unfortunately sustain some likelihood of neurologic decline. By the end of 6 months, more than half the patients will have a return of the pain and otherwise initially successful results. In Cowie and Hitchcock’s review of the literature, case series by Piscol (1385 patients) and then Mansuy and colleagues (124 patients) reported similar results of diminishing success after 1 year after open cordotomy from either cervical or thoracic lesions. It is also rare to consider re-lesioning the patient at a higher level.
These results, however, are appropriate for patients with severe medically refractory pain associated with metastatic cancer or high-grade lesions. It is not clear in the previously mentioned reviews whether the return of pain in patients with cancer who underwent cordotomy is due to failure of the lesion to hold, versus spread of the cancer to areas that are not encompassed by the lesion. The immediate pain relief following cordotomy is seen within moments of the lesion when done percutaneously (see later in this article) and within a day when the patient awakens from surgery for open cordotomy. Many of these patients actually need to be watched carefully postoperative because of the significant reduction in pain medications after successful cordotomy. It is gratifying to offer this focal neurosurgical procedure to patients who have minimal benefit from more generalized medical management. It many times will allow terminal patients to enjoy quality time with family while in their terminal phases of disease. Open thoracic cordotomy is an appropriate consideration in patients who have lower quadrant cancer pain and either cannot undergo an awake percutaneous cordotomy procedure or have significant risk of respiratory complications.
Percutaneous Cordotomy
Percutaneous cordotomy deserves separate discussion on technique, outcomes, and complications when compared with open cordotomy. Many excellent detailed reviews and discussions are present in the literature. Tasker’s discussion recently in 2009 is most useful for those who wish to understand the initial description, evolution of techniques, and successful strategies for this procedure. Today percutaneous cordotomy is performed using radiofrequency ablation reported first by Rosomoff and colleagues in 1965. However, the initial use of a percutaneous ablation for pain in the cervical cord was performed a few years earlier in 1963 by Mullan and colleagues using a strontium needle inserted into the STT. The use of radiofrequency techniques has significant advantages to lesion creation and, therefore, is still the most commonly used lesioning technique. The ability to test the effect of the attempted lesion, the ability to control the size of the lesion by adjusting time and temperature, and the ability to perform this in awake patients without the risk of general anesthesia continue to be significant advantages to this method of cordotomy over the open procedure.
Lesioning technique
Percutaneous cordotomy is normally performed through an orthogonal, transcutaneous approach to the C1/2 interspace. The goal is to initially identify the STT via stimulation and physiologic confirmation, and then to create a lesion that encompasses the contralateral pain and sensory perception usually from the trunk pelvis and leg. Fig. 4 illustrates the anatomic relationships of successful passage of the percutaneous lesioning electrode into the STT at C1/2. As mentioned previously, a few key anatomic concepts must be remembered:
- 1.
Entry into the spinothalamic tract occurs within 1 to 2 mm anterior to the dentate ligament
- 2.
Sacral and lumbar fibers are initially encountered on penetration, with cervical and thoracic fibers lying more medial and anterior
- 3.
The impedance of the electrode changes dramatically when passing from CSF into the parenchyma of the cord
- 4.
Respiratory control lies immediately medial to the STT and is approximately 4 to 5 mm anterior into the cord.
With the patient supine and given intermittent light sedation, the identification of the approach to the C1 to 2 interspace is done with the assistance of fluoroscopy or x-ray in the past, and more recently with CT guidance. The patient’s head must be immobilized to avoid sudden movement when the needle is placed into the spinal cord. Liberal use of local anesthetic will allow insertion of the needle percutaneously through an orthogonal approach into the dura with minimal patient discomfort, as long as no anesthetic is delivered intrathecally. With the patient in a supine position, the needle needs to be placed just anterior to the dentate ligament, so visualization of the dentate ligament is the requisite step in locating the needle correctly before insertion into the spinal cord. The unavailability of oil-based contrast agents (eg, Pantopaque) has been replaced by the use of water-soluble contrast (eg, Omnipaque) or a small amount of air, which can delineate the dentate ligament.
Once the needle is appropriately positioned just anterior to the dentate ligament, it can then be advanced into the spinal cord. Before doing so it is important to measure the impedance of the electrode and note the rise from approximately 300 to 400 Ω to more than 1000 Ω on entering the spinal cord white matter. Usually, penetration of the pia results in a brief increase in local pain reported by the patient. The location of the electrode can be seen at this point by imaging and confirmed many times by examination of the patient with electrical stimulation.
Stimulation using low frequency (2–5 Hz) is used to create a motor response twitching in the ipsilateral neck muscles with low stimulus strength indicating presence of the needle to anterior or near the anterior roots. Twitching of the ipsilateral arm, shoulder, trunk, or leg muscles at low stimulus indicates that the tip is near the corticospinal tract and should be repositioned more anteriorly. Sensory stimulation is best done by switching the frequency to a higher rate (approximately 100 Hz). The patient should report contralateral sensory phenomena: usually a feeling of warmth or cold in the trunk or lower extremities contralateral to the stimulus. This should overlay the area of pain closely. If the patient reports ipsilateral arm or occipital paresthesias, the electrode is too posterior and lies, in fact, dorsal to the dentate ligament. Evoked sensory phenomena in the contralateral hand generally implies a good location for the electrode.
The electrode with a 2-mm exposed tip is typically used for creating the lesion following stimulation. Several versions of these electrodes are now available commercially and the reader is encouraged to review the articles by Kanpolat. Once the lesioning electrode is physiologically confirmed to be located in the STT, then the lesion is performed. This is usually created at 70 to 80°C for approximately 60 seconds (30–40 mA for 30–60 seconds). The patient is examined during and after the lesioning procedure for any signs of motor weakness. Extent of analgesia can be documented once the lesion is completed. Ideally, documentation of decreased pinprick sensation should cover the entire painful area. If the extent of analgesia is not adequate, the electrode can be slightly repositioned and an additional lesion can be created by using the same parameters. When bilateral cordotomies are needed, they should be separated by at least a week to minimize the unwanted side effects of this procedure.
Complications of percutaneous cordotomy
Similar to open cordotomy, inadvertent damage to the spinal cord beyond the STT is the reason complications are seen. Table 4 lists the complications seen in one of the largest reported series of percutaneous cordotomy (2616 patients; Lorenz and colleagues ). Mortality reported with this procedure (3% on average) is likely related to respiratory suppression (Ondine curse) and seen only with bilateral procedures. Other complications that are routinely reported in descending order are bladder dysfunction (7.6%), temporary ipsilateral weakness (7.6%), ataxia (4.0%), respiratory dysfunction (3.5%), and permanent ipsilateral weakness (1.0%). Although many believe that medial extension of the lesion is keyed to successful dense analgesia in the contralateral painful region, this increases the risk of respiratory complications. Another poorly discussed risk factor for complications with this procedure is the presence of terminal disease in the patients for whom this procedure is selected.
Related posts:
Introduction to Neuropathic Pain Syndromes
Intracranial Ablative Procedures for the Treatment of Chronic Pain
Microvascular Decompression for Trigeminal Neuralgia
Neurolysis, Neurectomy, and Nerve Repair/Reconstruction for Chronic Pain
Nerve Blocks for Chronic Pain
Transcranial Magnetic Stimulation for Chronic Pain
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