Microsurgical anatomy of dorsal root entry zone of brachial plexus

Dorsal root entry zone lesioning for brachial plexus avulsion - technical evolution and long-term follow-up

BACKGROUND

Brachial plexus avulsion (BPA) injuries can cause severe deafferentation pain. This has been successfully treated with dorsal root entry zone (DREZ) lesioning. Distortions in anatomy following a BPA injury can make identifying neural structures challenging. We describe a modification to the operative technique that improves the surgical view and the advanced intraoperative neuromonitoring (IONM) employed to identify DREZ. We have analysed the long-term outcomes for pain, quality of life, and complications in patients undergoing DREZ lesioning.

METHODS

This is a single-centre retrospective case series including patients who underwent DREZ lesioning with IONM for brachial plexus avulsion between 2012 and 2022. Analysed data included pre- and postoperative pain (VAS), quality of life score for chronic pain, and complications. The evolution of the surgical approach is discussed.

RESULTS

44 consecutive patients underwent a DREZ lesioning procedure with intraoperative monitoring and mapping. In these patients the mean VAS score improved from 8.9 (7-10) to 1.87 (0-6) (p < 0.0001) at the time of discharge. 31 patients were followed-up for more than 12 months with a mean duration of follow-up of 41 months and their results were as follows: the mean VAS improved from 9.0 (7-10) to 4.1 (0-9) (p < 0.0001) at the last follow-up and the mean QOL values improved from 3.7 (2-6) to 7.4 (4-10) (p < 0.0001). The long-term outcomes were 'good' in 39%, 'fair' in 29% and 'poor' in 32% of patients. 55% of the patients were able to stop or reduce pain medications.

CONCLUSIONS

Modifications of surgical technique provide better exposure of DREZ, and IONM aids in identifying DREZ in the presence of severe intra-dural changes. Long-term outcomes of DREZ lesioning indicate not only a reduction in pain but also a significant improvement in quality of life.

Anatomical description of the ventral and dorsal cervical rootlets in rats: A microsurgical study

Purpose:

To describe the anatomical aspects of the cervical rootlets and to quantify the number of rootlets that compose C1 to T1.

Methods:

Twenty male rats were used in this study. The dorsal rootlets from C1 to T1 were analyzed. To study the ventral rootlets, the posterior root avulsion was performed using a microhook, allowing exposure of the ventral roots through manipulation of the denticulate ligament and arachnoid mater. The parameters analyzed were the number of ventral and dorsal rootlets by side and level.

Results:

The formation of the respective spinal nerve was observed in the spinal roots the union of the ventral and dorsal roots. In four animals the C1 spinal root had no dorsal and/or ventral contribution. There is no normal pattern of numerical normality of the dorsal and ventral rootlets. The average number of fascicles per root was 4.08, with a slight superiority on the left side. There was a slight superiority of the dorsal rootlets compared to the ventral rootlets.

Conclusions:

This investigation was the first to study cervical rootlets in rats. In 20% of the sample studied, the dorsal root of C1 was absent mainly on the left side. There is a nonlinear numerical increase from C1 to T1 in the rootlets. There is a numerical predominance of cervical fascicles on the left side, confronting several studies related to the functional predominance of right laterality, requiring new studies that correlate these variables.

Segment-Specific Orientation of the Dorsal and Ventral Roots for Precise Therapeutic Targeting of Human Spinal Cord

OBJECTIVE

To provide precise description of the dorsal and ventral roots orientation along with the main spinal cord anatomical measurements and their segment-specific variations.

PATIENTS AND METHODS

We collected and analyzed the measurements of the spines, spinal cords, and dorsal and ventral roots (C2-L5) of nine adult cadavers (five males and four females).

RESULTS

This study for the first time provides analysis of the dorsal and ventral roots orientation along with spinal cord anatomical measurements and their segment-specific distribution. The results of this study showed less variability in rostral root angles compared with the caudal. Dorsal and ventral rootlets were oriented mostly perpendicular to the spinal cord at the cervical level and had more parallel orientation to the spinal cord at the thoracic and lumbar segments. The number of rootlets per root was greatest at dorsal cervical and lumbar segments. Spinal cord transverse diameter and width of the dorsal columns were largest at cervical segments. The strongest correlation between the spinal cord and vertebrae structures was found between the length of intervertebral foramen to rostral rootlet distance and vertebral bone length.

CONCLUSION

These results demonstrate consistent variation in spinal cord anatomical features across all tested subjects. The results of this study can be used to locate spinal roots and main spinal cord landmarks based on bone marks on computed tomography or X-rays. These results could improve stereotactic surgical procedures and electrode positioning for neuromodulation procedures.

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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Brachial plexus avulsion neuropathic refractory pain: association of spinal cord stimulation and DREZotomy for complex pain

A 52-year-old male was involved in a car accident 30 years ago. He presented with complete motor paralysis of the left upper limb. This evolved into severe neuropathic pain (mainly shocking and burning sensation) distributed from C5 to T1 dermatomes. He was first treated with spinal cord stimulation (SCS), which did not show efficacy for pain control, maintaining high visual analog scale (VAS) scores. He then received complementary treatment with left cervical DREZotomy to mitigate suffering and preserve SCS function to control “mirror pain.”

The video can be found here: https://youtu.be/iTvbLAZ3odM

The Geometry of the roots of the Brachial Plexus

Diffusion tensor magnetic resonance imaging (DTI) can be used to reconstruct the brachial plexus in 3D via tracts connecting contiguous diffusion tensors with similar primary eigenvector orientations. When creating DTI tractograms, the turning angle of connecting lines (step angle) must be prescribed by the user; however, the literature is lacking detailed geometry of brachial plexus to inform such decisions. Therefore, the spinal cord and brachial plexus of 10 embalmed adult cadavers were exposed bilaterally by posterior dissection. Photographs were taken under standardised conditions and spatially calibrated in MATLAB. The roots of the brachial plexus were traced from the dorsal root entry zone for 5 cm laterally using a 2.5‐mm² Cartesian grid overlay. The trace was composed of points connected by lines, and the turning angle between line segments (the step angle) was resolved. Our data show that the geometry of the roots increased in tortuosity from C5 to T1, with no significant differences between sides. The 1^st thoracic root had the most tortuous course, turning through a maximum angle of 56° per 2.5 mm (99% CI 44° to 70°). Significantly higher step angles and greater variability were observed in the medial 2 cm of the roots of the brachial plexus, where the dorsal and ventral rootlets coalesce to form the spinal root. Throughout the brachial plexus, the majority of step angles (>50%) were smaller than 20° and <1% of step angles exceeded 70°. The geometry of the brachial plexus increases in tortuosity from C5 to T1. To reconstruct 99% of tracts representing the roots of the brachial plexus by DTI tractography, users can either customise the step angle per root based on our findings or select a universal threshold of 70°.

Microsurgical anatomy of the spinal cord in human fetuses

PURPOSE

To determine the microsurgical features of the spinal cord and ventral and dorsal rootlets in fetal period.

METHODS

Twelve formalin-fixed fetuses (six females and six males) with a mean gestational age of 27.0 ± 2.04 weeks (range between 25 and 32 weeks) were dissected to evaluate morphological properties of the spinal cord and rootlets.

RESULTS

Length and width of each spinal cord segment, number of dorsal and ventral rootlets, length of dorsal root entry and ventral root exit zones of each spinal nerve, spinal cord termination level, and the whole spinal cord length were determined in all fetuses. Contrary to previous reports, the number of ventral rootlets was always more than that of dorsal rootlets in all segments. No statistically significant gender difference was found for all parameters. Rootlet number and segment width in cervical region were larger than those of thoracic, while the lengths of dorsal root entry and ventral root exit zones in thoracic region were longer than those of cervical. In lumbar region, dorsal and ventral rootlet numbers were increasing again, while lengths of dorsal root entry and ventral root exit zones were decreasing. Number of dorsal and ventral rootlets of C5 and C6 segments was statistically higher than other cervical segments. The mean spinal cord length was found as 105.55 ± 11.30 mm and there was a positive significant relationship with gestational age. Conus medullaris level was detected between L1 and L3 segments.

CONCLUSION

Detailed microsurgical data about the fetal spinal cord and the dorsal and ventral rootlets presented in this study provide significant information which may be essential during surgical interventions in early postnatal period and childhood targeting the spinal cord and spinal nerve roots.

Post-mortem 11.7 Tesla Magnetic Resonance Imaging vs. Polarized Light Imaging Microscopy to Measure the Angle and Orientation of Dorsal Root Afferents in the Human Cervical Dorsal Root Entry Zone

Background: Destruction of the afferents by dorsal root entry zone (DREZ) surgery may be an effective treatment of intractable neuropathic pain, though it remains a high-risk surgical intervention. Potential complications due to the lesioning of structures within the cervical spinal cord other than the DREZ can be minimized by accurate knowledge of the optimal insertion angle [i.e., the angle between the DREZ and the posterior median sulcus (PMS)]. The employed insertion angle was based on measurements between the DREZ and the PMS on post-mortem transverse slices. However, new, more sophisticated imaging techniques are currently available and are thought to yield higher spatial resolution and more accurate images.

Obejctive: This article measures the angle between the DREZ and the PMS on 11.7T post-mortem magnetic resonance images and compares these findings with polarized light imaging (PLI) microscopy images of the same specimens in order to quantify fiber orientation within the DREZ.

Methods: To visualize the anatomy of the cervical DREZ, magnetic resonance imaging (MRI), diffusion-weighted MRI (dMRI), probabilistic tractography, and PLI were performed on three post-mortem human cervical spinal cords at level C5–C6. The MR data was used to measure the angle between the DREZ and the PMS. MR images were complemented by probabilistic tractography results. Then, the orientation of fibers within the DREZ was quantified by use of PLI microscopy.

Results: Median angle between the DREZ and the PMS, as measured on MR-images, was found to be 40.1° (ranging from 34.2° to 49.1°) and 39.8° (ranging from 31.1° to 47.8°) in the left and right hemicord, respectively. Median fiber orientation within the DREZ, as quantified by PLI, was 28.5° (ranging from 12.0° to 44.3°) and 27.7° (ranging from 8.5° to 38.1°) in the left and right hemicord, respectively.

Conclusion: Our study, which provides an improved understanding of the anatomy of the DREZ, the angle between the DREZ and the PMS and the median fiber orientation within the DREZ, could contribute to safer DREZ-lesioning surgery to treat chronic neuropathic pain in the future.

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.

Microanatomy of the brachial plexus roots and its clinical significance

PURPOSE

To provide the anatomical basis of brachial plexus roots for the diagnosis and treatment of brachial plexus root avulsion injury.

METHODS

The morphological features of brachial plexus roots were observed and measured on 15 cervicothoracic spine of adult cadavers. The relationship of brachial plexus nerve roots and the surrounding tissues also were observed, as well as the blood supply of anterior and posterior roots of the brachial plexus.

RESULTS

Origination of the nerve roots in the dorsal-ventral direction from the midline was fine-tuned at each level along the spinal cord. The minimum distance of the origin of the nerve root to midline was 2.2 mm at C ₅, while the maximum was 3.1 mm at T ₁. Inversely, the distance between the origin of the posterior root and the midline of the spinal cord gradually decreased, the maximum being 4.2 mm at C ₅ and minimum 2.7 mm at T ₁. Meanwhile, there was complicated fibrous connection among posterior roots of the brachial plexus. The C _5-6 nerve roots interlaced with tendons of the scalenus anterior and scalenus medius and fused with the transverse-radicular ligaments in the intervertebral foramina. However, these ligaments were not seen in C _7-8, and T ₁. The blood supply of the anterior and posterior roots of the brachial plexus was from the segmental branches of the vertebral artery, deep cervical artery and ascending cervical artery, with a mean outer diameter of 0.61 mm.

CONCLUSIONS

The systematic and comprehensive anatomic data of the brachial plexus roots provides the anatomical basis to diagnose and treat the brachial plexus root avulsion injury.

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.

Dorsal root entry zone lesion, midline myelotomy and anterolateral cordotomy

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.

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

BACKGROUND

The posterolateral sulcus (PLS) is an important surgical landmark, especially for DREZ (dorsal root entry zone) operations.

METHODS

The present study aimed to show the variations of the PLS using human spinal cord histological sections and report the variability in the number of dorsal rootlets of the spinal nerves in each the spinal cord segment. Further, measure the height and width of the dorsal horn on histological sections for cervical, thoracic, and lumbar levels.

RESULTS

The results of the present study showed various patterns of PLS 1.clearly present PLS, 2. short PLS, 3. absent PLS or 4. irregular PLS. Height and width measurements of the dorsal horn showed that the average width was greatest at lower cervical (0.48 ± 0.04 mm) and least at lower thoracic levels (0.41 ± 0.04 mm), whereas the average height was greatest at upper cervical (3.0 ± 0.06 mm) and smallest at lower lumbar levels (1.8 ± 0.08 mm). The average number of rootlets varied considerably, at cervical level it was 7.6 ± 1.4 mm, at thoracic 6.6 ± 0.8 mm and at lumbar 6.1 ± 0.4 mm.

CONCLUSIONS

The detailed anatomy of the variations of the PLS and the average number of rootlets at each spinal level can increase the success of regional surgery. Further, fine measurements on histological sections can give detailed knowledge on the size necessary for lesioning in DREZ operations.

Microsurgical anatomy of the dorsal thoracic rootlets and dorsal root entry zones

BACKGROUND

For successful DREZ (dorsal root entry zone) surgery, optimal neuroanatomical orientation and precise microsurgical dissection are required. Although cervical, lumbar, and sacral spinal segments have been studied in detail, such information is not available for thoracic segments. The objective of this anatomical study is to comprehensively illustrate the microanatomical features of the thoracic DREZs and their variations.

METHODS

Fifteen formalin-fixed adult cadaveric spinal cords from T1 to T12 were used. The dorsal rootlet numbers, distance between the posteromedial and posterolateral sulcus, length of each DREZ, length of each segment, and mean length of the dorsal rootlets were measured under a surgical microscope.

RESULTS

The longest DREZs were observed at the T6, T7, and T8 segments with mean values of 15.3 mm, 15.6 mm, and 15.4 mm, respectively. The longest segment was observed at the T10 segment with a mean value of 21.0 mm, and the shortest segment was observed at the T1 segment with a mean value of 13.5 mm.

CONCLUSIONS

The highest dorsal rootlet density is at the T1 segment of the spinal cord, can be easily distinguished visually, and may be a useful surgical landmark. The DREZs in T6-7 segments are longest, while these two segments have the least number of rootlets. Because the dorsolateral tract is remarkably narrow and the dorsal horn is exceedingly deep, DREZ surgery at the thoracic level may be difficult and risky for the dorsal column and corticospinal tract. Acquaintance with the microanatomy of the DREZ in the thoracic spinal cord is crucial to DREZ surgery.