Dorsal Root Entry Zone Lesions

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CHAPTER 171 Dorsal Root Entry Zone Lesions

Diaa Bahgat, Dibyendu K. Ray, Kim J. Burchiel

Management of chronic pain has graduated over the past few decades to a multidisciplinary approach, and neurosurgical methods, the mainstay of the neurosurgeon’s armamentarium, have evolved from mostly ablative to mostly neuromodulatory. Neuroaugmentative procedures such as spinal cord stimulation have gained increasing acceptance in recent years, largely because of their minimal invasiveness. Additionally, the substantial and prolonged pain relief obtained with these procedures, their cost-effectiveness, the ability to repeatedly reprogram implant technology, and the rarity of complications have all influenced the adoption of neuromodulation as the current surgical pain treatment of choice. Ablative procedures, in particular, percutaneous approaches, nevertheless remain a standard form of treatment of certain conditions such as trigeminal neuralgia. More traditional destructive procedures, such as anterolateral cordotomy, remain an option for patients with certain cancer-related pain such as Pancoast’s syndrome or breakthrough pain resistant to pharmacotherapy. Dorsal root entry zone (DREZ) lesions, although not as frequently performed as a few decades ago, remain a potent form of therapy for management of pain from brachial plexus avulsion and other spinal cord injuries (SCIs) and several types of cancer pain.¹^,² Nucleus caudalis DREZ has been shown to be effective in the treatment of anesthesia dolorosa, atypical facial pain, postherpetic pain, and some deafferentation pain.³

Pain Mechanism

Pain-signaling impulses originating in peripheral nociceptors are transmitted by first-order neurons, which have their cell bodies in the dorsal root ganglion. These fibers are either small myelinated (Aδ) or unmyelinated (C) axons that carry impulses from polymodal nociceptors or nociceptive-specific terminals, respectively.⁴ Second-order neurons, with cell bodies in the dorsal horn of the spinal cord, cross the midline and ascend in the contralateral spinothalamic tract to relay in the thalamus, from where third-order neurons project to the postcentral gyrus (via the internal capsule).

The “H”-shaped configuration of the gray matter of the spinal cord was first described by Rolando in 1824.⁵ Subsequently, Rexed described discrete laminae in the central gray matter of the spinal cord. The significance of this arrangement in the dorsal horn is that unmyelinated C fibers synapse in laminae I and II whereas the small myelinated Aδ fibers synapse in laminae I, II, and V. C fibers project to the spinoreticulodiencephalic tract (also known as the paleospinothalamic tract), whereas Aδ fibers project to the anterolateral white funiculus (also known as the neospinothalamic tract).^4,⁶^–⁹

Abnormal electrical activity has been documented in the dorsal horn in experimental animal models of brachial plexus avulsion and other SCIs. The concept of DREZ lesions involves surgical destruction of these second-order neurons of the ascending nociceptive pathway. Destruction of the DREZ and superficial dorsal horn is thought to abolish this abnormal electrical activity and thus help relieve pain.¹⁰^,¹¹

Historical Perspectives

Attempts at DREZ lesions were first made in 1972 in Lyon, France, by Sindou.^2,¹² He successfully used a technique of microcoagulation of the dorsal rootlets in a patient with Pancoast’s syndrome and termed the procedure selective posterior rhizotomy. Further attempts at the procedure were made by Nashold and colleagues in 1974 with radiofrequency (RF) thermocoagulation.²^,¹³ They coined the term DREZ operation and championed the merits of the procedure. Later, success was reported with lasers by Levy and coworkers, Powers and associates, and Stranjalis and Torrens¹⁴^–¹⁸ and with ultrasonic techniques for DREZ lesions by Dreval and Kandel and associates.¹⁹^,²⁰ In recent years, Spaic and coauthors have advocated a microsurgical technique of incising the dorsolateral sulcus and suctioning the dorsal horn, but it would appear that pain control rates with this technique are not statistically different (P < .5) from the standard procedure.²¹

Anatomic and Physiologic Considerations

In his classic paper, Sindou noted that in the dorsal horn of the spinal cord, afferent fibers are segregated spatially according to their size and destination.^2,¹² About 1 mm outside the spinal cord, the large and small fibers in the dorsal roots, which are arranged somewhat randomly in the afferent nerve fibers, undergo reorientation. Each dorsal root divides into 4 to 10 rootlets, each 0.25 to 1.5 mm in diameter and varying according to level.^2,¹² The small myelinated and unmyelinated fibers carrying nociceptive impulses course to the lateral side, which makes them appropriately situated to enter into the tract of Lissauer, where they run for one or two segments before penetrating the gray matter of the spinal cord.^4,^22,²³ Because the nociceptive fibers preferentially terminate in lamina I and the substantia gelatinosa (laminae II and III), they are amenable, by virtue of their superficial position in the spinal cord, to surgical lesions without substantial risk of damage to other ascending or descending pathways.^7,²³^–²⁵ In a human cadaveric study of DREZ lesions in the cervicothoracic region, it was found that the average number of rootlets of the C5 to T1 roots was approximately 7.76 + 3.2, with C6 having the most rootlets. The average angle of the inferior rootlets with the longitudinal axis of the spinal cord at each root level from C5 to T1 decreased gradually from 65.6 ± 3.68 to 19.8 ± 2.98 degrees. On cross-sectional studies it was noted that the average length of the dorsal horn was 3.47 ± 0.31 mm (range, 3.10 to 3.75 mm) and the average width was 1.35 ± 0.07 mm (1.20 to 1.45 mm). The angle between the longitudinal axis of the dorsal horn and the sagittal plane of the spinal cord decreased gradually from 29 to 43 degrees, with an average of 35.9 ± 1.28 degrees.²⁶

The dorsal horn essentially consists of central projections of primary neurons, intrinsic dorsal horn neurons, and ascending and descending tracts. It is theorized that the final mechanism underlying pain after SCI is deafferentation, which leads to permanent anatomic and neurochemical changes in the intrinsic dorsal horn neurons and thereby results in chronic pain. It is also possible that the modulating effect of the descending inhibitory impulses on the dorsal horn neurons is modified or lost in such cases.^23,^27,²⁸ Woolf proposed a classification of the different physiologic states (modes) of the dorsal horn: mode 1—control state; mode 2—suppressed state (as in neurostimulation); mode 3—sensitized state; and mode 4—reorganized state.²⁹ Mode 4 represents a potentially irreversible reorganization of the circuitry of the dorsal horn region. A shift from mode 1 to mode 4 occurs when the highly structured organization of the dorsal horn is modified by degenerative or traumatic changes, which leads to alteration of sensory processing in the dorsal horn. Loss of afferent input to the dorsal horn neurons may also result in upregulation of postsynaptic receptors (denervation hypersensitivity) and adversely affect segmental modulatory (inhibitory) mechanisms, thereby dramatically altering processing of input in the dorsal horn.^4,^22,^23,²⁷ Regeneration may also occur at these sites, and it has been documented that the large myelinated fibers that normally terminate in the deeper laminae may grow into lamina II (the site of C-fiber terminals).⁴^,²³ The formation of new synapses would therefore affect the way that the central nervous system processes low-threshold mechanical impulses and lead to their perception as pain. DREZ lesions may interrupt the mechanism of such pain by ablation of the dorsal horn structures involved in generating nociceptive impulses as a result of deafferentation. When Falci and colleagues performed electrophysiologic studies on the DREZ for intraoperative guidance in patients with SCI, they documented spontaneous electrical hyperactivity (higher voltage and frequencies) in the region.¹⁰ Using this as a guide to localization of the DREZ, they were able to achieve 100% pain relief in 88% of their patients.

Indications

Since introduction of the technique, DREZ lesions have been applied to treat a wide range of pain conditions, most of which are a form of central or deafferentation pain caused by different conditions ranging from brachial plexus avulsion, SCI, phantom limb, and other complex regional syndromes. DREZ lesions have also been applied to treat pain conditions caused by herpes zoster, cancer, and even spasticity.^11,³⁰^–³²

Despite a plethora of study data, specific application of DREZ lesions and safety guidelines are lacking.³³

Brachial Plexus Injury Pain

Avulsion of the dorsal root and the resultant gliosis lead to scar formation in the dorsal horn and substantia gelatinosa. Such scar formation may give rise to loss of the inhibitory effects of large-caliber sensory fibers and to spontaneous activity in nociceptive-specific and wide–dynamic range (polymodal) neurons, which may be responsible for perception of pain after brachial plexus lesions.³⁴^,³⁵

Brachial plexus injuries are frequently associated with avulsion of the dorsal or ventral root, or both, from their associated entry zones into the spinal cord. This leads to the production of deafferentation pain in up to 20% to 30% of patients with brachial plexus injuries.³⁶ Brachial plexus avulsion pain may begin immediately after the trauma, but its onset can also occur months to years later. Pain projection depends primarily on the extent of the injury and the number of avulsed roots involved; it may include the whole upper limb but usually radiates to the forearm and hand.

Multiple groups have extensive experience with the application of DREZ lesions to treat pain from brachial plexus avulsion injury. Sindou and coauthors reported that 42% of patients had complete avulsion of all plexus roots; they also noticed scarring, arachnoiditis, and atrophy of the spinal cord, which in some cases was rotated. They reported that 66% of patients had good to excellent outcomes, with 71% demonstrating an improvement in daily activities (mean follow-up was 6 years).³⁷ Friedman and colleagues reported similar results: 77% of patients had a 75% reduction in pain intensity.³⁸^,³⁹ Prestor reported that 47.6% of patients had complete resolution of pain whereas 80.9% had at least 70% improvement. He noticed that better results were obtained in patients who underwent surgery more than 1 year after injury and reported poor results in patients previously treated with pain management surgery such as cordotomy or myelotomy.¹¹ In a long-term follow-up study, Chen and associates reported early good results in 80% of patients operated on by thermocoagulation; however, this number dropped to 60% (5-year follow-up) and 50% (10-year follow-up).⁴⁰^,⁴¹ Samii and colleagues reported a 50% reduction in pain in 86% of patients immediately postoperatively, in 68% after 3 months, in 63% after 6 months, and in 62% in long-term follow-up. They found no correlation between the number of roots avulsed or the extent of the DREZ coagulation procedure performed and the degree of pain reduction, between the duration of pain and outcome after DREZ, or between pain onset and time to surgery.⁴² Dreval applied ultrasound to perform DREZ lesioning and operated on 127 patients. He reported that 96% of patients had immediate improvement and 87% had a good result at follow-up (average follow-up of 47.5 months).¹⁹

Spinal Cord Injury Pain

The incidence of all types of chronic pain after SCI has been variously reported to be between 18% and 94%.⁴³^–⁴⁵ This variability would seem to be dependent on the population surveyed, the survey method, and pain types included (mild and moderate). An incidence of pain of around 65% after SCI is a good first approximation.⁴⁶ In a longitudinal study of the prevalence and characteristics of pain in the first 5 years after SCI, Siddall and associates found that musculoskeletal pain was the most commonly experienced type of pain (59%).⁴⁷

Reports vary on the incidence of neuropathic pain after SCI, with estimates varying between 10% and 25%.^33,^48,⁴⁹ Pain may occur immediately after injury or be delayed for several years and usually has a burning character.⁵⁰^,⁵¹ Neuropathic pain after SCI has been divided into “at level” and “below level.” The incidence of at-level and below-level neuropathic pain has variously been reported to be 13% to 51% and 27% to 42%, respectively, after SCI.⁴⁷^,⁵² Werhagen and coauthors reported that the incidence of neuropathic injury pain is lower in younger patients (26% in patients younger than 20 years at time of injury versus 58% in patients older than 20 years). Furthermore, below-level pain is more common in SCI patients younger than 40 years, whereas at-level pain is more prevalent in patients older than 40 years at the time of injury.⁴⁷^,⁵²

Pain of neuropathic or deafferentation origin after SCI may be perceived at the involved injury segment (i.e., segmental pain). It may also be located below the level (i.e., infralesional or deep-seated visceral pain). SCI pain is complex, and other mechanisms that may lead to pain, such as spinal instability, should also be considered and corrected before deciding to perform a DREZ lesion.

Sindou and associates reported good long-term results in 65% of patients with segmental pain and 0% improvement in those with infrasegmental pain. A good result was obtained in 88% of patients with predominantly paroxysmal pain, whereas only 26% with continuous pain had good results.³¹ Nashold and Bullitt reported good results in 77%,⁵⁰ whereas Sampson and coworkers reported that 54% of patients were pain free after 3 years’ follow-up and noted better results in patients with incomplete injuries.⁵³ Richter and Seitz reported good results with DREZ lesions in the cervical spinal cord for brachial plexus avulsion and poor results in paraplegic patients with infrasegmental pain; patients with cervical pain experienced a 30% recurrence rate.⁵⁴ Kanpolat and coauthors reported good results in 47% of patients with segmental pain.³⁰ Friedman and Nashold reported a 50% improvement over a 6-month to 6-year interval in patients with segmental pain rather than diffuse pain.³⁹

Selection of patients for DREZ lesions is critical in those with SCI pain. Studies such as the ones just cited have shown that patients with pain in the segmental region after spinal cord trauma experience a better response than do those who have diffuse pain or pain that is below the injured segment.^30,^31,^38,^51,⁵⁵ Caution should be exercised when performing DREZ lesions in patients with incomplete SCI to avoid aggravation of weakness by performance of an overly deep or aggressive lesion. In the case of complete SCI, a deep lesion can, of course, be more safely performed.

Phantom Limb Pain

DREZ lesions should not be considered the first line of treatment in patients with pain after peripheral nerve injuries. It should be applied only in select patients and only after failure of other medical and surgical methods such as spinal cord stimulation.

Good results have been reported when the pain has a paroxysmal character or allodynia (perception of pain from what would ordinarily be a nonpainful stimulus) is a prominent feature. Good results can also be achieved in posttraumatic cases.⁵¹ Patients with phantom limb pain who also have nerve root avulsion may also have good results. Stump pain is not usually relieved unless it is of a paroxysmal type.¹¹ Saris and colleagues operated on patients with pain from a phantom limb secondary to trauma, gangrene, and cancer and reported complete relief of the pain in 36%.⁵⁶ Malin and Winkelmuller also reported good results in patients with peripheral nerve injuries that were associated with root avulsion.⁵⁷ Prestor reported that DREZ lesions for peripheral nerve injuries and phantom limb pain were generally unsatisfactory but may have a role in select cases.¹¹

Cancer Pain

Attempts at DREZ lesions were first made in 1972 for Pancoast-Tobias syndrome by Sindou.²^,¹² Since then, several other options to treat cancer pain have emerged, such as midline myelotomy, image-guided cordotomy, and intrathecal pump administration of opioids, which has limited the use of DREZ lesioning to treat cancer pain.

A cancer pain candidate for DREZ lesions should have a life expectancy that can be measured in years rather than months or weeks and have pain that is well localized. DREZ lesions can be applied to pain subserved by the cervical, thoracic, or lumbosacral spinal cord, such as that caused by tumors affecting peripheral nerves, plexuses, or roots. DREZ lesions can also be indicated for pain caused by malignant invasion of the abdominal or thoracic wall or the pelvic floor.

Care should be taken when performing DREZ lesions on the lumbosacral spine to avoid lower extremity weakness or sphincteric dysfunction, and thus it should be a limited procedure.

Sindou and associates reported good results in 87% of patients undergoing treatment at the cervical or cervicothoracic level and in 78% undergoing treatment at the lumbar level.⁵¹^,⁵⁸ Kanpolat and coauthors reported pain relief in 60% of patients with neuropathic pain of cancer origin.³⁰

Postherpetic Neuralgia

Postherpetic neuralgia is typically located at the thoracic level, where the dorsal horn is very narrow, and injury to the dorsal column in this area can lead to loss of proprioception in the lower extremities.

Prestor performed DREZ lesions in 4 patients with postherpetic neuralgia and achieved an excellent outcome in 3. These patients all had pain confined to a segmental area that could be localized.¹¹ Friedman and Nashold reported good pain relief in 8 of 12 patients in short-term follow-up,⁵⁹ and good pain relief persisted in long-term follow-up in 25%.³⁶ Kanpolat and colleagues operated on only 2 patients and achieved complete pain relief in both.³⁰

Spasticity

The spasticity-relieving effect of DREZ lesions is probably due to interruption of both the myotonic monosynaptic reflex and the nociceptive polysynaptic reflex; these reflexes are excitatory to the dorsal horn somatosensory relay center, which has been cut off from higher central control. Conversely, DREZ lesions may preserve the inhibitory, lemniscal intersegmental input on the dorsal horn.⁶⁰^–⁶⁵

Sindou and coworkers studied the effect and outcome of DREZ lesions in patients with spasticity. They performed DREZ lesions from C5 to T1 on patients with spastic hemiparesis and reported good outcomes in shoulder and elbow tone yet disappointing results in hand and finger tone.⁶⁶^,⁶⁷ In patients with spastic paraplegia, Sindou and coauthors reported 87% improvement in tone, which allowed easy passive movement. Patients with both pain and spasticity also had an 88% improvement in pain. Sindou’s group noted that spasticity secondary to SCI had a better outcome than that caused by multiple sclerosis. Patients with spasticity of cerebral origin showed the least improvement and highest complication rate. Postoperative sensory disturbance was noted in all patients and was severe in 20%.^64,⁶⁶^–⁶⁸

Other Indications

Kahilogullari and coauthors reported performing cervical DREZ lesions on a patient with dystonia after thalamotomy and campotomy and achieved a good outcome.⁶⁹

Teixeira and associates used cervical DREZ lesions to treat patients with postradiation plexopathy. The patients had complete relief except for one, in whom the pain recurred. Transient urinary retention and motor weakness were also observed.⁷⁰

Operative Technique

Preoperative Considerations

Prescreening of patients for DREZ lesions is critical to ensure no confusion between musculoskeletal pain and neuropathic pain. It is important to determine that the patient has been treated appropriately with pharmacologic measures for neuropathic pain, including gabapentin, pregabalin, and antidepressants, before DREZ lesions are considered. Finnerup and coworkers observed that only 7% of patients suffering from symptoms suggestive of neuropathic pain have actually been prescribed drugs considered to be effective in the management of neuropathic pain.⁴³

In patients with brachial plexus injuries, pain develops in the deafferentated arm in up to 90%; at 3 years after injury, pain is mild in 51% and severe in 40%.⁷¹ However, more than 90% of patients with avulsion injuries may suffer significant pain.³⁷^,⁷² Use of brachial plexus grafting and nerve transfers should be also be considered because it has been reported that up to 80% of patients may be pain free or nearly pain free at 2 years’ follow-up after nerve reconstruction.⁷³^,⁷⁴

Anesthesia, Premedication, and Positioning

The standard DREZ operation is a microsurgical procedure performed with the patient under general anesthesia in the prone position. If the cervical region is to be accessed, the head should be secured by pin fixation for easier positioning and adequate access to the operative site. The “Concorde” position with the head and neck flexed may also be used to avoid loss of cerebrospinal fluid (CSF).² The prophylactic use of preoperative intravenous steroids at doses corresponding to those used for the management of acute SCI has been advocated. The use of fluoroscopy helps mark the site of surgical intervention on the skin surface.

Surgical Procedure

A laminectomy or hemilaminectomy is performed that corresponds to the vertebral level of the spinal cord segment involved, as determined by a dermatomal pain pattern. It is prudent to obtain exposure of the cord up to two segments proximal to the involved upper segmental level to assist in localization of the dorsolateral sulcus by visualization of the entry point of the normal rootlets rostral to the injury. In most cases of brachial plexus avulsion injury, the laminectomy should extend from the upper border of C3 up to and including C7, with undercutting of the T1 lamina.^11,^37,⁷⁵ In cases of brachial plexus avulsion, the DREZ can be localized by the presence of pitting on the dorsolateral aspect of the spinal cord, where the dorsal rootlets have been avulsed. Partially avulsed roots can be identified by a change in root color or size.² Comparison with the contralateral side and tracing the dorsolateral sulcus by identifying the rostral and caudal normal rootlets can also help localize the DREZ.³⁷ Sindou has reported DREZ angles at various levels: 30 degrees at C6, 26 degrees at T4, 37 degrees at T12, and 36 degrees at L3.²

Dorsal horn postsynaptic potentials may help in identification of spinal cord segments,¹⁰^,⁷⁵ and somatosensory evoked potentials can be monitored to confirm continued integrity of the dorsal column fibers. Microelectrode recording in the injured segments has also been reported to be useful in the performance of DREZ lesions.¹⁰

After the pia of the DREZ is incised with an arachnoid knife, microsurgical lesions are made by thermal coagulation with fine-tipped bipolar forceps at a low setting. The lesions are made in “staccato” fashion along the DREZ (4- to 5-mm lesions, with a gap of a few millimeters between each lesion). This allows DREZ lesioning without causing additional and uncontrolled injury from eversion of spinal cord tissue along a long pial incision. A lesional depth of 2 to 3 mm in the dorsal horn is sufficient to produce a lesion in the nucleus proprius (laminae IV to V) because the superficial layers of Lissauer’s tract and the superficial dorsal horn may already have been avulsed. The DREZ under any retained rootlet at the level of interest may be disrupted further by partial sectioning of the ventrolateral aspect of the rootlet.²^,⁷⁶

Special Considerations

In DREZ lesions for pain from brachial plexus avulsion injury, a hemilaminectomy from C3 to T1 with preservation of the spinous processes allows sufficient exposure. The ventral roots can be stimulated to confirm the segments (C5—deltoid; C6—biceps; C7—triceps; C8 to T1—small muscles of the hand).¹¹^,³⁷

At the lumbosacral level it is prudent to isolate and preserve the posterior spinal artery by freeing it from the dorsolateral sulcus. The rich vascularity of the conus makes performance of microsurgical DREZ lesions difficult in this region. Added to this is the fact that the lower lumbar roots exit from the intervertebral foramina well below the level of exposure, thus making their identification difficult. In the case of S2 to S4, it is not easy to conduct simple electrophysiologic studies to identify them (cystomanometry or rectomanometry is required).

For the RF lesion method proposed by Nashold and colleagues, a 0.5-mm-diameter insulated stainless steel electrode with a 2-mm tip is used, and lesions are made with a current strength of 35 to 40 mA at less than 75°C for 10 to 15 seconds. A “chain-link” pattern is used, with 2- to 3-mm intervals between adjacent lesions (Fig. 171-1A). The lesion usually extends 1 to 2 mm beyond the tip of the electrode. Nashold and associates have also recommended measuring impedance during surgery after they determined that the impedance of damaged spinal cord was less than 1200 Ω whereas that of a normal spinal cord reaches 1500 Ω.^2,⁷⁵⁷⁶

FIGURE 171-1 A, A radiofrequency (RF) electrode is used along the dorsal root entry zone (DREZ) in a case of root avulsion pain. RF lesions are made 2 to 3 mm deep along a line that is formed by a combination of several landmarks: (1) a line directly connecting the last intact dorsal rootlet rostrally with the first visible intact rootlet distally, (2) the “pits” left by the avulsed roots, and (3) a small vein that typically runs just lateral to the DREZ, which may still be present. RF lesions are made 1 to 2 mm apart in a nearly continuous line that covers the length of the cord segment where root avulsion has occurred. B, An alternative method for creating DREZ lesions is to coagulate along the line of the DREZ, as described in A. A series of myelotomies 2 to 3 mm deep are then made with a microknife, at which point slightly open bipolar tips are placed in the myelotomy with the power setting at 20 to 25, and coagulation is performed for several seconds. Each myelotomy is 5 to 7 mm in length, with 2 mm of pia left intact between lesions; coagulation is performed between adjacent myelotomies by placing the bipolar tips into contiguous lesions and coagulating. As with RF lesions, these bipolar DREZ myelotomies are made in a nearly continuous line that covers the length of the cord segment where root avulsion has occurred.

An alternative to the RF procedure is to use bipolar cautery with the power set at 20 to 25 and extend the DREZotomy for root avulsion pain by first coagulating over the surface along a zone that is formed by a combination of several landmarks: (1) a line directly connecting the last intact dorsal rootlet rostrally with the first visible intact rootlet distally, (2) the “pits” left by the avulsed roots, and (3) a small vein that typically runs just lateral to the DREZ, which may still be present. It is a combination of these available landmarks that delineates the line for the DREZ lesions in each individual case. DREZ lesions are made through the coagulated zone with a microknife to a depth of 2 mm, and then the bipolar tips are inserted into the myelotomy to a depth of 2 mm, opened slightly, and coagulation current applied for several seconds. Each lesion measures 5 to 7 mm along the DREZ, and lesions are made in segments such that 1 to 2 mm of intact pia is left between the lesions to prevent eversion of spinal cord tissue from a long linear myelotomy. The zone between each lesion is similarly coagulated by placing one tip of the bipolar cautery into adjacent lesions and applying coagulating current for several seconds (Fig. 171-1B). The object of a DREZ lesion is to coagulate strictly within the dorsal horn, approximately to the level of the nucleus proprius (laminae IV to V). Precise placement of the lesion is critical to avoid injury to the dorsal column medially and the corticospinal tract laterally (Fig. 171-2).

FIGURE 171-2 Radiofrequency or bipolar myelotomy dorsal root entry zone (DREZ) lesions are performed 2 to 3 mm deep in the dorsal horn while recognizing that the superficial layers of the DREZ have probably been avulsed with the dorsal root. The depth of the lesion, by either method, is such that the nucleus proprius (laminae IV to V) is coagulated. The trajectory of the lesion must account for and avoid the dorsal column medially and the corticospinal tract laterally.

Carbon dioxide (CO₂), argon, and Nd:YAG (neodymium: yttrium-aluminium-garnet [Nd:Y₃Al₅O₁₂]) lasers have all been used to create DREZ lesions.^14,^16,¹⁸ Levy and colleagues advocated a pulse duration of 0.1 second, 20-W power, and one to two pulses to create a 2-mm-deep lesion at an angle of 45 degrees to the DREZ. For SCI pain, Stranjalis and Torrens used an Nd:YAG laser to create lesions at 1-mm intervals to a depth of 2 mm at a power output of 10 W/sec, with the lesions extending 3 cm above and below the involved segment.¹⁸ In his analysis of lesions made by RF and lasers, Young reported that although lasers produced a V-shaped lesion, RF lesions were mostly spherical.⁷⁷ He also noted that RF resulted in better pain control, but at the cost of a higher complication rate.

Nashold and coworkers had used intraoperative ultrasonography to localize and drain intraspinal cysts after root avulsion.⁴⁹ Dreval, at the Moscow Central Institute, reported using ultrasound at 44 KHz and an amplitude of 15 µm to 50 pm to create a “sulcomyelotomy” along the dorsolateral sulcus at an angle of projection of 25 degrees medially and ventrally.¹⁹ His procedure keeps vessels crossing the sulcus intact.

Spaic and coauthors reported a technique of microsurgical suctioning of the dorsal horn in place of the coagulation procedure.²¹ They advocated use of a 0.8-mm suction tip to suction the dorsal horn under microscopic visualization after opening the dorsolateral sulcus. According to these authors, the dorsal horn can be visualized at 20× magnification as a band of gray substance that gradually reaches the massive central gray matter of the cord.

Complications

Complications of DREZ lesions, as with all procedures, can include the general complications of infection, meningitis, CSF leak, and hematoma formation. Other complications specifically related to the procedure can also occur and may be caused by injury to neighboring structures such as the dorsal column, pyramidal tract, or dorsal spinocerebellar tract. Neurological complications tend to be more common in DREZ surgery performed on the thoracic spine because of the narrow dorsal horn.³⁸^,⁵⁹ Such complications include dysesthesia, hypoesthesia, ataxia, motor weakness, and urogenital dysfunction, all of which may be either temporary or permanent.³³^,⁵¹

Edgar and coworkers operated on 112 patients with SCI and reported sensory deficit in 2, motor deficit in 3, CSF leak in 3, pulmonary embolism in 2, and myoclonus in 5.⁷⁸ Freidman and colleagues operated on 54 patients and reported CSF leak in 9, epidural hematoma in 1, weakness in 2, bladder insufficiency in 2, and new dysesthesia in 2.³⁹ Chen and Tu used RF-induced DREZ lesions to treat 500 patients with brachial plexus injuries; ataxia developed in 25% but improved within 3 months.⁴¹ Sindou and Jeanmonod operated on 53 patients with spasticity and found that 48% had worse trophic skin changes, which at follow-up improved in just 10.9%. They attributed this complication to (1) surgical stress as a result of poor nutritional condition, (2) decreased sensation on dermatomes affected by the DREZ lesion, and (3) progression and decompensation of underlying disease (mainly multiple sclerosis). They also noted that 12.5% had increased bladder dysfunction and 3.8% experienced CSF leaks.⁶⁸ Prestor operated on 40 patients with deafferentation pain and reported that transient sensory loss developed in 15%, mainly in the form of proprioceptive deficit secondary to injury to the dorsal spinocerebellar tract, which improved within 8 weeks. Permanent superficial and deep sensory disturbance with weakness was observed in 1 patient (2.5%).¹¹

Some differences in the rate of complications between alternative methods of performing DREZ lesions have been reported. Young found more deficits with RF when performed on an area of 0.5 × 2 mm than with laser or RF on an area of 0.25 × 2 mm.⁷⁹