Clinical anatomy of the C1 dorsal root, ganglion, and ramus: a review and anatomical study

The effect of physical therapy integrated with pharmacotherapy on tension-type headache and migraine in children and adolescents

BACKGROUND

Tension-type headache (TTH) and migraine are prevalent neurological conditions in children and adolescents that significantly impact activity of daily living (ADL) and quality of life (QOL). Although physical therapy targeting cervical myofascial trigger points (MTrPs) on TTH and migraine has been extensively studied in adults, the efficacy in pediatric patients remains unexplored. The aim of this study is to reveal the effect of physical therapy integrated with pharmacotherapy on TTH and migraine in children and adolescents.

METHODS

We conducted a prospective, observational cohort study recruiting consecutive patients aged 6 to 18 years with TTH and migraine with cervical MTrPs. They were classified into 4 types of headaches: frequent episodic TTH (FRTTH), chronic TTH (CTTH), episodic migraine (EM) and chronic migraine (CM). The once-weekly 40-minutes physical therapy session integrated with pharmacotherapy (integrated physical therapy) was continued until the treatment goals (headache days per week less than 2 days, headache impact test-6 (HIT-6) score to below of 50, and the ability to attend school daily) was achieved. Multifaceted assessments including headache frequency (headache days per week), headache intensity using the Visual Analogue Scale (VAS), pain catastrophizing score (PCS), hospital anxiety and depression scale (HADS) score, HIT-6 scores, and EuroQol 5 dimensions 5-level questionnaire (EQ-5D-5 L) scores, were conducted to evaluate the treatment effects.

RESULTS

161 patients were enrolled in this study. 106 patients (65.8%) were diagnosed with TTH: 70 (66.8%) with FETHH, 36 (34.0%) with CTTH, and 55 patients (34.2%) were diagnosed with migraine: 43 patients (78.2%) with EM, 12 patients (21.8%) with CM. We observed significant improvements in headache frequency, headache intensity, PCS, HADS score, HIT-6 scores, and EQ-5D-5 L scores before and after the treatment in all 4 types of headaches. The average number of sessions required to achieve the treatment goals was 4 times (weeks) for patients with FETTH and EM, 5.5 for those with CTTH, and 7.5 for those with chronic migraine.

CONCLUSION

The integrated physical therapy on pediatric TTH and migraine patients with the cervical MTrPs was significantly effective in reducing headache symptoms and improving ADL and QOL.

Mechanisms of Action of Dorsal Root Ganglion Stimulation

The dorsal root ganglion (DRG) serves as a pivotal site for managing chronic pain through dorsal root ganglion stimulation (DRG-S). In recent years, the DRG-S has emerged as an attractive modality in the armamentarium of neuromodulation therapy due to its accessibility and efficacy in alleviating chronic pain refractory to conventional treatments. Despite its therapeutic advantages, the precise mechanisms underlying DRG-S-induced analgesia remain elusive, attributed in part to the diverse sensory neuron population within the DRG and its modulation of both peripheral and central sensory processing pathways. Emerging evidence suggests that DRG-S may alleviate pain by several mechanisms, including the reduction of nociceptive signals at the T-junction of sensory neurons, modulation of pain gating pathways within the dorsal horn, and regulation of neuronal excitability within the DRG itself. However, elucidating the full extent of DRG-S mechanisms necessitates further exploration, particularly regarding its supraspinal effects and its interactions with cognitive and affective networks. Understanding these mechanisms is crucial for optimizing neurostimulation technologies and improving clinical outcomes of DRG-S for chronic pain management. This review provides a comprehensive overview of the DRG anatomy, mechanisms of action of the DRG-S, and its significance in neuromodulation therapy for chronic pain.

Scientific and Regulatory Policy Committee Technical Review: Biology and Pathology of Ganglia in Animal Species Used for Nonclinical Safety Testing

Dorsal root ganglia (DRG), trigeminal ganglia (TG), other sensory ganglia, and autonomic ganglia may be injured by some test article classes, including anti-neoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, nerve growth factor inhibitors, and aminoglycoside antibiotics. This article reviews ganglion anatomy, cytology, and pathology (emphasizing sensory ganglia) among common nonclinical species used in assessing product safety for such test articles (TAs). Principal histopathologic findings associated with sensory ganglion injury include neuron degeneration, necrosis, and/or loss; increased satellite glial cell and/or Schwann cell numbers; and leukocyte infiltration and/or inflammation. Secondary nerve fiber degeneration and/or glial reactions may occur in nerves, dorsal spinal nerve roots, spinal cord (dorsal and occasionally lateral funiculi), and sometimes the brainstem. Ganglion findings related to TA administration may result from TA exposure and/or trauma related to direct TA delivery into the central nervous system or ganglia. In some cases, TA-related effects may need to be differentiated from a spectrum of artifactual and/or spontaneous background changes.

Scientific and Regulatory Policy Committee Points to Consider: Sampling, Processing, Evaluation, Interpretation, and Reporting of Test Article-Related Ganglion Pathology for Nonclinical Toxicity Studies

Certain biopharmaceutical products consistently affect dorsal root ganglia, trigeminal ganglia, and/or autonomic ganglia. Product classes targeting ganglia include antineoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, and anti-nerve growth factor agents. This article outlines "points to consider" for sample collection, processing, evaluation, interpretation, and reporting of ganglion findings; these points are consistent with published best practices for peripheral nervous system evaluation in nonclinical toxicity studies. Ganglion findings often occur as a combination of neuronal injury (e.g., degeneration, necrosis, and/or loss) and/or glial effects (e.g., increased satellite glial cell cellularity) with leukocyte accumulation (e.g., mononuclear cell infiltration or inflammation). Nerve fiber degeneration and/or glial reactions may be seen in nerves, dorsal spinal nerve roots, spinal cord, and occasionally brainstem. Interpretation of test article (TA)-associated effects may be confounded by incidental background changes or experimental procedure-related changes and limited historical control data. Reports should describe findings at these sites, any TA relationship, and the criteria used for assigning severity grades. Contextualizing adversity of ganglia findings can require a weight-of-evidence approach because morphologic changes of variable severity occur in ganglia but often are not accompanied by observable overt in-life functional alterations detectable by conventional behavioral and neurological testing techniques.

Best Practices for Dorsal Root Ganglion Stimulation for Chronic Pain: Guidelines from the American Society of Pain and Neuroscience

With continued innovations in neuromodulation comes the need for evolving reviews of best practices. Dorsal root ganglion stimulation (DRG-S) has significantly improved the treatment of complex regional pain syndrome (CRPS), and it has broad applicability across a wide range of other conditions. Through funding and organizational leadership by the American Society for Pain and Neuroscience (ASPN), this best practices consensus document has been developed for the selection, implantation, and use of DRG stimulation for the treatment of chronic pain syndromes. This document is composed of a comprehensive narrative literature review that has been performed regarding the role of the DRG in chronic pain and the clinical evidence for DRG-S as a treatment for multiple pain etiologies. Best practice recommendations encompass safety management, implantation techniques, and mitigation of the potential complications reported in the literature. Looking to the future of neuromodulation, DRG-S holds promise as a robust intervention for otherwise intractable pain.

Dural arteriovenous fistula of the craniocervical junction along the first cervical nerve: A single-center experience and review of the literature

BACKGROUND

Dural arteriovenous fistulas (DAVFs) of the craniocervical junction (CCJ) are relative rare lesions. Most studies of DAVFs of the CCJ included the fistulas at the foramen magnum, first cervical (C1), and second cervical (C2) level. DAVFs of the CCJ along C1 spinal nerve are rare vascular lesions with distinctive features. Our aim is to review cases of DAVFs of the CCJ along C1 spinal nerve at our institution.

METHODS

From June 2008 and December 2021. We reviewed a consecutive series of intracranial and spinal DAVFs at our institution and collected all patients harboring DAVFs of the CCJ along C1 spinal nerve. Medical charts were retrospectively reviewed regarding patient demographic data (i.e., gender and age), presenting symptoms and signs, treatment methods, and neurological outcome and complications after treatment. All image studies, including cranial computed tomography (CT) scan, cervical magnetic resonance imaging, CT angiography, and digital subtraction angiography (DSA) with rotational CT angiography were analyzed by experienced neuroradiologists. The authors also review of the literature of DAVFs of the C1 spinal nerve.

RESULTS

The authors identified 7 patients, including 5 men (71.4 %) and 2 women (28.6 %) with median age 54 years, range 48-72 years. Subarachnoid hemorrhage (SAH) occurred in 5 (71.4 %) patients, and progressive myelopathy in 2 (28.6 %). All fistulas except one received blood supply from the radiculomeningeal branch of the VA at C1 level. Venous aneurysms, being the source of bleeding, were detected in all fistulas with SAH. All patients except one were treated by surgical management. One fistula was treated by balloon-assisted Onyx embolization. Most patients had good neurological outcome following surgery. Complete obliteration of all fistulas treated by surgery was confirmed by follow-up DSA obtained 1 week after surgery. Two patients developed temporary pain and spasm of the trapezius muscle after the surgery. One patient resulted in poor neurological outcome and died due to sepsis and acute upper gastrointestinal bleeding one month after failed embolization. For patients with SAH, only one patient required ventriculoperitoneal shunt.

CONCLUSIONS

DAVFs of the CCJ along the first spinal nerve are rare and a unique subtype of DAVFs at the CCJ. These fistulas account for 1.74 % of all intracranial and spinal DAVFs in the present study. SAH is the major manifestation of DAVFs at C1 spinal nerve that may be overlooked on routine initial DSA. Rotational CT angiography is useful for clarification of the angioarchitecture of these fistulas, including small feeding artery and venous varix. Surgical treatment by interruption of the intradural draining vein should be the treatment of choice for C1 spinal nerve DAVF.

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.

Intra-dural intercommunications between dorsal roots of adjacent spinal nerves and their clinical significance

PURPOSE

The dorsal roots of adjacent spinal nerves are known to communicate with each other through rami communicantes. These intercommunications can cause deviations in the normal dermatomal organization which leads to errors during clinical decision-making. The objective of the study was to augment the existing knowledge of these communications which shall help minimize the diagnostic and therapeutic errors.

METHODS

The present study examined thirty cadaveric spinal cord specimens to document the data of intra-dural, intercommunications between dorsal roots of adjacent spinal nerves.

RESULTS

All the regions of the spinal cord exhibited the presence of intercommunications with variable frequency. The intercommunications were categorized into a total of nine groups based on their patterns. The levels of spinal cord exhibiting higher and lower frequencies of intercommunications were identified.

CONCLUSION

This information will be useful during the clinical evaluation of patients with spinal cord pathologies or radiculopathies. The outcomes of rhizotomy can also be improved with knowledge of intercommunications.

A Review of the History, Anatomy, and Development of the C1 Spinal Nerve

The C1 spinal nerve is a fascinating anatomic structure owing to its wide range of variations. Throughout history, understanding of the cranial and spinal nerves has probably influenced the current conception of this nerve among anatomists. Located at the craniocervical junction, the C1 spinal nerve contributes to the motor innervation of deep cervical muscles through the cervical (anterior) and Cruveilhier's (posterior) plexuses. Sensory functions of this nerve are more enigmatic; despite investigations into its dorsal rootlets, a dorsal root ganglion, and the relationships between this nerve and adjacent cranial and spinal nerves, there is still no consensus regarding its true anatomy. In this article, we review the available literature and discuss some of the developmental models that could potentially explain the wide range of variations and functions of the C1 nerve.

Human Dorsal Root Ganglia

Sensory neurons with cell bodies situated in dorsal root ganglia convey information from external or internal sites of the body such as actual or potential harm, temperature or muscle length to the central nervous system. In recent years, large investigative efforts have worked toward an understanding of different types of DRG neurons at transcriptional, translational, and functional levels. These studies most commonly rely on data obtained from laboratory animals. Human DRG, however, have received far less investigative focus over the last 30 years. Nevertheless, knowledge about human sensory neurons is critical for a translational research approach and future therapeutic development. This review aims to summarize both historical and emerging information about the size and location of human DRG, and highlight advances in the understanding of the neurochemical characteristics of human DRG neurons, in particular nociceptive neurons.

Nanoconjugate-bound adenosine A1 receptor antagonist enhances recovery of breathing following acute cervical spinal cord injury

Respiratory complications in patients with spinal cord injury (SCI) are common and can have a negative impact on the quality of patients' lives. Previously, we found that intradiaphragmatic administration of the nanoconjugate-bound A₁ adenosine receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) induced recovery of diaphragm function following SCI in rats. When administered immediately following the injury, recovery was observed as early as 3days following SCI and it persisted until the end of the study, 28days after the drug delivery. The recovery was observed using diaphragmatic electromyography (EMG) as well as phrenic nerve recordings; both of which were conducted under anesthetized conditions. Confounding effects of anesthetic may make data interpretation complex in terms of the impact on overall ventilatory function and clinical relevance. The objective of the present study was to test the hypothesis that intradiaphragmatic administration of nanoconjugate-bound DPCPX, enhances recovery of ventilation following SCI in the unanesthetized rat. To that end, Sprague-Dawley rats underwent C2 spinal cord hemisection (C2Hx) on day 0 and received either: (i) 0.15μg/kg of nanoconjugate-bound DPCPX or (ii) vehicle control (50μl distilled water). To assess ventilation, unrestrained whole body plethysmography (WBP) was performed on day 0 (immediately before the surgery) and 3, 7, 14, 21 and 28days following the SCI. Frequency, tidal volume, and minute ventilation data were analyzed in two minute bins while the animal was calm and awake. We found that a single administration of the nanoconjugate-bound A₁ adenosine receptor antagonist facilitated recovery of tidal volume and minute ventilation following SCI. Furthermore, the treatment attenuated SCI-associated increases in respiratory frequency. Taken together, this study suggests that the previously observed DPCPX nanoconjugate-induced recovery in diaphragmatic and phrenic motor outputs may translate to a clinically meaningful improvement in ventilatory function in patients with SCI.

Spinal Cord Anatomy and Clinical Syndromes

We review the anatomy of the spinal cord, providing correlation with key functional and clinically relevant neural pathways, as well as magnetic resonance imaging. Peripherally, the main descending (corticospinal tract) and ascending (gracilis or cuneatus fasciculi and spinothalamic tracts) pathways compose the white matter. Centrally, the gray matter can be divided into multiple laminae. Laminae 1-5 carry sensitive neuron information in the posterior horn, and lamina 9 carries most lower motor neuron information in the anterior horn. Damage to the unilateral corticospinal tract (upper motor neuron information) or gracillis-cuneatus fasciculi (touch and vibration) correlates with ipsilateral clinical findings, whereas damage to unilateral spinothalamic tract (pain-temperature) correlates with contralateral clinical findings. Damage to commissural fibers correlates with a suspended bilateral "girdle" sensory level. Autonomic dysfunction is expected when there is bilateral cord involvement.

Intradural communication between dorsal rootlets of spinal nerves: their clinical significance

BACKGROUND

Anatomical and surgical textbooks give almost no attention to the intradural communications between dorsal rootlets of adjacent spinal nerves. These communications can be of significance in various neurosurgical procedures and clinical conditions of the region.

METHODS

The spinal cord of six formaldehyde-fixed cadavers was dissected from C1-S5. The dorsal rootlets of the spinal nerves were exposed via a posterior approach and communications between adjacent spinal nerves were documented.

RESULTS

The frequency of communication between adjacent dorsal rootlets of the spinal nerves showed variations among spinal levels. Thirty-eight dorsal rootlet communications were observed in six cadavers (12 sides) and 20 (52.6%) were at cervical levels, 14 (36.8%) at thoracic levels, and four (10.5%) at lumbar levels. The majority of communications were observed on the left side (65.8%). Communications were most frequently observed at cervical (C4-C5, C5-C6) and upper thoracic (T1-T2) levels and seen least frequently at lower thoracic and lumbar levels. No communications were observed at sacral levels. Five types of communication were observed: I. oblique ascending, II. oblique descending III. short Y, IV. long Y and V shaped. None of the communication extended beyond one segment at any spinal level. The occurrence of such dorsal rootlet communications ranged from 3 to 7 for each cadaver and the mean was 4.8 ± 1.3. Histological sections from various levels of the dorsal rootlet communications showed that all consisted of myelinated fibers of varying diameters.

CONCLUSIONS

Such communications may lead to misinterpretation of the pathology on the basis of clinical signs and symptoms and also should be considered in rhizotomy.

Microscopic clusters of sensory neurons in C1 spinal nerve roots and in the C1 level of the spinal accessory nerve in adult humans

This study examined C1 spinal nerve roots and their anastomotic connections with the spinal accessory nerve for histological evidence of sensory neurons in adult humans. C1 spinal nerves and roots with the adjacent segments of the spinal accessory nerve and the spinal cord were dissected en bloc from cadaveric specimens, and prepared for histological study. Results show that in 39.3% of specimens studied, no sensory component to the C1 spinal nerve could be identified. The C1 dorsal root was present 35.7% of the time, and when present it always contained neuronal cell bodies. In the remaining specimens, the sensory contribution to the C1 spinal nerve came through an anastomotic connection with the spinal accessory nerve. The investigators were able to identify clusters of neuronal cell bodies along the spinal accessory nerve at the level of C1 in 100% of the specimens examined.

Pain referral patterns of the C1 to C3 nerves: implications for headache disorders

The cervical nerves may play a significant role in primary headache disorders. We reviewed the patterns of pain evoked by stimulation of the first 3 cervical nerves (C1-C3) in 10 patients with chronic occipital pain, 6 of whom also had migraine. Stimulation at the C1 level evoked periorbital and frontal pain in 6 of 6 patients with migraine but evoked occipital or cervical pain in those without migraine. C2 and C3 stimulation resulted in occipital or cervical pain in all patients. The C1 nerve may have an important sensory function in headache disorders that have orbital and frontal pain as a prominent feature.

Symptomatic occipitocervical paracondylar process

A paracondylar process is a bony exostosis that arises from the skull base lateral to the occipital condyle and extends inferiorly toward the transverse process of the atlas. This congenital anomaly can vary in size from a small protuberance to an elongated process articulating with an epitransverse process arising from C-1. Typically, a paracondylar process is an incidental finding described in anatomical studies. The authors report on a patient with a symptomatic paracondylar process articulating with an epitransverse process that caused occipitocervical pain. Resection of the paracondylar and epitransverse processes completely relieved the patient's pain.

Classification and clinical anatomy of the first spinal nerve: surgical implications

Object

Data regarding the first cervical nerve are scanty and conflicting, however this nerve may need to be identified for neurosurgical procedures such as rhizotomy for torticollis and suboccipital pain syndromes. The authors performed the present study to elucidate further the detailed anatomy of the first cervical nerve and review its clinical relevance.

Methods

Forty adult cadavers (80 sides) were used in this study. Dissection was performed at the craniocervical junction with special attention to the formation and presence of the components of the C-1 spinal nerve. Additionally, connections between the C-1 nerve and the spinal accessory nerves were recorded.

Results

The authors classified the C-1 nerves into Types Ia, Ib, and II, in 34, 9, and 37 sides, respectively. Type Ia was composed of ventral and dorsal roots with a dorsal root ganglion, Type Ib was composed of ventral and dorsal roots and no dorsal root ganglion, and Type II was composed of only ventral roots. All types contained both dorsal and ventral rami. Mackenzie's nerve was identified on 2 left sides (2.5%). On 48 sides (60%), the C-1 nerve received a mean of 2.5 dorsal rootlets. In the remaining specimens, C-1 did not receive any dorsal rootlets. On the sides found to receive C-1 dorsal rootlets, 14 (30%) were found to have a distinct dorsal root ganglion present, and in 21 (44%) the spinal accessory nerve joined with the dorsal rootlets. The first cervical vertebra in these cases did not possess a dorsal root ganglion. A dorsal ramus of the C-1 spinal nerve was identified on all sides. Communication between the dorsal rami of C-1 and C-2 near their posterior elements was found on 12 sides (15%).

Conclusions

A detailed knowledge of C-1 nerve anatomy may be of use to the surgeon operating in the vicinity. Specifically, this knowledge may be helpful in procedures involving C-1 rhizotomy, including peripheral denervation procedures for cervical dystonia and occipital neuralgia.