Anatomy of the spinal dorsal root entry zone: its clinical significance

A Literature Review of Dorsal Root Entry Zone Complex (DREZC) Lesions: Integration of Translational Data for an Evolution to More Accurate Nomenclature

The purpose of this translational review was to provide evidence to support the natural evolution of the nomenclature of neuromodulatory and neuroablative radiofrequency lesions for pain management from lesions of individualized components of the linear dorsal afferent pathway to “Dorsal Root Entry Zone Complex (DREZC) lesions.” Literature review was performed to collate anatomic and procedural data and correlate these data to clinical outcomes. There is ample evidence that the individual components of the DREZC (the dorsal rami and its branches, the dorsal root ganglia, the dorsal rootlets, and the dorsal root entry zone) vary dramatically between vertebral levels and individual patients. Procedurally, fluoroscopy, the most commonly utilized technology is a 2-dimensional x-ray-based technology without the ability to accurately locate any one component of the DREZC dorsal afferent pathway, which results in clinical inaccuracies when naming each lesion. Despite the inherent anatomic variability and these procedural limitations, the expected poor clinical outcomes that might follow such nomenclature inaccuracies have not been shown to be prominent, likely because these are all lesions of the same anatomically linear sensory pathway, the DREZC, whereby a lesion in any one part of the pathway would be expected to interrupt sensory transmission of pain to all subsequent more proximal segments. Given that the common clinically available tools (fluoroscopy) are inaccurate to localize each component of the DREZC, it would be inappropriate to continue to erroneously refer to these lesions as lesions of individual components, when the more accurate “DREZC lesions” designation can be utilized. Hence, to avoid inaccuracies in nomenclature and until more accurate imaging technology is commonly utilized, the evidence herein supports the proposed change to this more sensitive and inclusive nomenclature, “DREZC lesions.”

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Anatomical and technical factors affecting the neural response to epidural spinal cord stimulation

OBJECTIVE

Spinal cord stimulation (SCS) is a common neurostimulation therapy to treat chronic pain. Computational models represent a valuable tool to study the potential mechanisms of action of SCS and to optimize the design and implementation of SCS technologies. However, it is imperative that these computational models include the appropriate level of detail to accurately predict the neural response to SCS and to correlate model predictions with clinical outcomes. Therefore, the goal of this study was to investigate several anatomic and technical factors that may affect model-based predictions of neural activation during thoracic SCS.

APPROACH

We developed computational models that consisted of detailed finite element models of the lower thoracic spinal cord, surrounding tissues, and implanted SCS electrode arrays. We positioned multicompartment models of sensory axons within the spinal cord to calculate the activation threshold for each sensory axon. We then investigated how activation thresholds changed as a function of several anatomical variables (e.g. spine geometry, dorsal rootlet anatomy), stimulation type (i.e. voltage-controlled vs. current-controlled), electrode impedance, lead position, lead type, and electrical properties of surrounding tissues (e.g. dura conductivity, frequency-dependent conductivity).

MAIN RESULTS

Several anatomic and modeling factors produced significant percent differences or errors in activation thresholds. Rostrocaudal positioning of the cathode with respect to the vertebrae had a large effect (up to 32%) on activation thresholds. Variability in electrode impedance produced significant changes in activation thresholds for voltage-controlled stimulation (38% to 51%), but had little effect on activation thresholds for current-controlled stimulation (less than 13%). Changing the dura conductivity also produced significant differences in activation thresholds.

SIGNIFICANCE

This study demonstrates several anatomic and technical factors that can affect the neural response to SCS. These factors should be considered in clinical implementation and in future computational modeling studies of thoracic SCS.

Dorsal Root Entry Zone Lesion for Neuropathic Pain Due to Thoracolumbar Spine Fracture: Long-Term Result

OBJECTIVE

To retrospectively evaluate long-term efficacy and safety of dorsal root entry zone (DREZ) lesion for treatment of neuropathic pain within the lower extremities and perineal region after thoracolumbar spine fracture.

METHODS

Forty-two patients were treated with posterior laminectomy under general anesthesia. The DREZ regions of the spinal cord segments were ablated under a microscope. Data regarding pain relief, pain variation over time, and postoperative complications were collected. The relationship between injured spinal column segment, spinal cord, nerve root, and pain territory were analyzed retrospectively.

RESULTS

Spinal column injury segments were located between T12 and L4. Pain territories were distributed between the T11 and S5 dermatomes with varying ranges, at an average of 2-6 segments higher than the spinal cord injury segments. Pain relief rate was 100% in 21 patients (50.0%) and was over 50% in 14 patients (33.3%). Eighteen patients (42.9%) developed temporary tingling in the upper edge of the spinal cord lesion segment after surgery. Of the 4 patients with unilateral lower extremity pain, 2 developed postoperative persistent pain in the contralateral lower extremity.

CONCLUSIONS

For patients with neuropathic pain of the lower extremities and/or the perineal region after thoracolumbar spine fracture, pain within the lower extremities was mostly because of nerve root injury. Pain in the perineal region caused by L1 fracture was attributed to spinal cord injury segmental pain. Nerve root injury pain had a good prognosis after DREZ lesion; the effect of DREZ lesion for spinal cord injury segmental pain may be uncertain.

The Role of Functional Neuroanatomy of the Lumbar Spinal Cord in Effect of Epidural Stimulation

In this study, the neuroanatomy of the swine lumbar spinal cord, particularly the spatial orientation of dorsal roots was correlated to the anatomical landmarks of the lumbar spine and to the magnitude of motor evoked potentials during epidural electrical stimulation (EES). We found that the proximity of the stimulating electrode to the dorsal roots entry zone across spinal segments was a critical factor to evoke higher peak-to-peak motor responses. Positioning the electrode close to the dorsal roots produced a significantly higher impact on motor evoked responses than rostro-caudal shift of electrode from segment to segment. Based on anatomical measurements of the lumbar spine and spinal cord, significant differences were found between L1-L4 to L5-L6 segments in terms of spinal cord gross anatomy, dorsal roots and spine landmarks. Linear regression analysis between intersegmental landmarks was performed and L2 intervertebral spinous process length was selected as the anatomical reference in order to correlate vertebral landmarks and the spinal cord structures. These findings present for the first time, the influence of spinal cord anatomy on the effects of epidural stimulation and the role of specific orientation of electrodes on the dorsal surface of the dura mater in relation to the dorsal roots. These results are critical to consider as spinal cord neuromodulation strategies continue to evolve and novel spinal interfaces translate into clinical practice.

Surgical Outcomes of Posterolateral Sulcus Approach for Spinal Intramedullary Tumors: Tumor Resection and Functional Preservation

BACKGROUND

Selection of the access myelotomy is a key issue in surgery for spinal intramedullary tumors. This study focused on surgical outcomes with the posterolateral sulcus (PLS) approach, equivalent to dorsal root entry zone myelotomy.

METHODS

This retrospective study of the 10-year period from 2007 to 2016 included 90 cases of spinal intramedullary lesions (99 operations). A PLS approach was indicated for intramedullary lesions situated laterally in the spinal cord showing no contact with the spinal cord surface. Neurological conditions before and after surgery were carefully assessed objectively.

RESULTS

A PLS approach was applied in 34 of the 99 operations (34.3%). Among 70 cases involving astrocytic tumor, ependymal tumor, cavernous malformation or hemangioblastoma, 23 cases (32.9%) were operated on using a PLS approach. Microscopically gross total or subtotal removal of the tumor was achieved in 18 of 23 cases (78.3%). These 18 cases demonstrated mild deterioration of motor function on the approach side early after surgery, but usually resolving within several months postoperatively. Average grade of the modified McCormick functional schema before surgery was maintained 6 months postoperatively. Average grade of the sensory pain scale before surgery was significantly improved by 6 months postoperatively. Segmental dysesthesia on the approach side unexpectedly remained in 2 of 18 cases (11.1%) even late after surgery.

CONCLUSIONS

These findings suggest that the PLS approach can provide direct access to tumors with minimal tissue damage, when applied appropriately after careful case selection.

Modified dorsal root entry zone lesioning for intractable pain relief in patients with root avulsion injury

OBJECTIVE Dorsal root entry zone (DREZ) lesioning has been the most effective surgical treatment for the relief of intractable pain due to root avulsion injury, but residual pain and a decrease in pain relief in the follow-up period have been reported in 23%-70% of patients. Based on pain topography in the most recent studies on neuropathic pain, the authors modified the conventional DREZ lesioning procedure to improve clinical outcomes. The presumed rationale for this procedure is to eliminate the spontaneous discharges of neurons in the superficial spinal dorsal horn as well as wide dynamic range neurons in the deep spinal dorsal horn. METHODS Ten patients with avulsion-related pain underwent surgery between 2011 and 2015. The surgical procedure was described and postoperative pain relief was assessed as follows: excellent (residual pain never exceeded 3 on the visual analog scale [VAS] without medication), good (residual pain never exceeded 5 on the VAS with medication), and poor (residual pain was greater than 5 with medication). Specific perioperative complications were assessed. RESULTS The aim of this surgical procedure was to destroy the deeper layers of the posterior horn of spinal gray matter, which was in contrast to the procedures of Nashold and Sindou, which were to destroy the superficial layers. All patients achieved excellent (n = 7, pain relief without medication) or good (n = 3, pain relief with medication) pain relief postoperatively, and the recurrence of pain was not reported in any patients (median 29 months after surgery, range 12-64 months). Nine patients (90%) achieved complete pain relief (a score of 0 or 1 on the VAS) with or without medication. No surgical site complications such as infection or CSF leakage were noted. No motor deficit was observed in any patient. A sensory deficit was observed in 2 patients and disappeared within 1 month in 1 patient. New pain at the adjacent level of DREZ lesioning was observed in 3 patients and disappeared within 1 month in 2 patients. In the other patient, new pain persisted and required analgesics. CONCLUSIONS These preliminary results demonstrated that total and persistent global pain relief was achieved with the modified DREZ lesioning procedure in 90% of patients without major neurological deficits. The clinical improvements achieved by this modified surgical procedure support the hypothesis that not only the superficial layers, but also deeper layers of the spinal dorsal horn are associated with intractable pain due to root avulsion injury.

Magnetospinography visualizes electrophysiological activity in the cervical spinal cord

Diagnosis of nervous system disease is greatly aided by functional assessments and imaging techniques that localize neural activity abnormalities. Electrophysiological methods are helpful but often insufficient to locate neural lesions precisely. One proposed noninvasive alternative is magnetoneurography (MNG); we have developed MNG of the spinal cord (magnetospinography, MSG). Using a 120-channel superconducting quantum interference device biomagnetometer system in a magnetically shielded room, cervical spinal cord evoked magnetic fields (SCEFs) were recorded after stimulation of the lower thoracic cord in healthy subjects and a patient with cervical spondylotic myelopathy and after median nerve stimulation in healthy subjects. Electrophysiological activities in the spinal cord were reconstructed from SCEFs and visualized by a spatial filter, a recursive null-steering beamformer. Here, we show for the first time that MSG with high spatial and temporal resolution can be used to map electrophysiological activities in the cervical spinal cord and spinal nerve.

Clinical anatomy and significance of the thoracic intervertebral foramen: A cadaveric study and review of the literature

INTRODUCTION

The literature is lacking information on the anatomy and the osseous dimensions of the thoracic intervertebral foramen (IVF). We describe the anatomy of the broader area, and we proceed with morphometric data of the vertebrae and the foramina. Depiction of these features is provided with imaging and illustrations. The purpose of this paper is to survey and present the anatomy of the foramen as a whole and provide baseline statistical data.

MATERIALS AND METHODS

We review relevant literature, and we present data obtained from skeletal samples of known population and sex. One hundred and nineteen thoracic vertebrae of ten cadaveric spines from the prefecture of Eastern Macedonia and Thrace, Greece, were selected. Statistical analysis measuring the vertical height and the foraminal width of each vertebra was made in accordance with sex.

RESULTS

No statistically important differences referring to the descriptive data of both sexes were found. However, statistically, important positive correlation between the vertebral height and the foraminal width was observed, especially for men. The components of the foramen including arteries and veins passing through or neighboring it, and the spinal nerves and roots are described and depicted.

CONCLUSIONS

The osseous thoracic IVF reveals a glimpse of the in vivo structure and alterations of its width may be present in back pain and other degenerative diseases. Although it is crucial for surgeries and other interventional procedures of the thoracic spine, little is known about the precise anatomy and dimensions of this anatomical landmark.

Neuropathic pain after brachial plexus avulsion--central and peripheral mechanisms

REVIEW

The pain that commonly occurs after brachial plexus avulsion poses an additional burden on the quality of life of patients already impaired by motor, sensory and autonomic deficits. Evidence-based treatments for the pain associated with brachial plexus avulsion are scarce, thus frequently leaving the condition refractory to treatment with the standard methods used to manage neuropathic pain. Unfortunately, little is known about the pathophysiology of brachial plexus avulsion. Available evidence indicates that besides primary nerve root injury, central lesions related to the abrupt disconnection of nerve roots from the spinal cord may play an important role in the genesis of neuropathic pain in these patients and may explain in part its refractoriness to treatment.

CONCLUSIONS

The understanding of both central and peripheral mechanisms that contribute to the development of pain is of major importance in order to propose more effective treatments for brachial plexus avulsion-related pain. This review focuses on the current understanding about the occurrence of neuropathic pain in these patients and the role played by peripheral and central mechanisms that provides insights into its treatment. Pain after brachial plexus avulsion involves both peripheral and central components; thereby it is characterized as a mixed (central and peripheral) neuropathic pain syndrome.