Microsurgical Anatomy of the Hypoglossal and C1 Nerves: Description of a Previously Undescribed Branch to the Atlanto-Occipital Joint

Step-by-Step Dissection of the Extreme Lateral Transodontoid Approach to the Anterior Craniovertebral Junction: Surgical Anatomy and Technical Nuances

BACKGROUND

Multicompartmental lesions of the anterior craniovertebral junction require aggressive management. However, the lesions can be difficult to reach, and the surgical procedure is difficult to understand. The aim of this study was to create a procedural, stepwise microsurgical educational resource for junior trainees to learn the surgical anatomy of the extreme lateral transodontoid approach (ELTOA).

METHODS

Ten formalin-fixed, latex-injected cadaveric heads were dissected under an operative microscope. Dissections were performed under the supervision of a skull base fellowship-trained neurosurgeon who has advanced skull base experience. Key steps of the procedure were documented with a professional camera and a high-definition video system. A relevant clinical case example was reviewed to highlight the principles of the selected approach and its application. The clinical case example also describes a rare complication: a pseudoaneurysm of the vertebral artery.

RESULTS

Key steps of the ELTOA include patient positioning, skin incision, superficial and deep muscle dissection, vertebral artery dissection and transposition, craniotomy, clivus drilling, odontoidectomy, and final extradural and intradural exposure.

CONCLUSIONS

The ELTOA is a challenging approach, but it allows for significant access to the anterior craniovertebral junction, which increases the likelihood of gross total lesion resection. Given the complexity of the approach, substantial training in the dissection laboratory is required to develop the necessary anatomic knowledge and to minimize approach-related morbidity.

ACR Appropriateness Criteria® Cranial Neuropathy: 2022 Update

Cranial neuropathy can result from pathology affecting the nerve fibers at any point and requires imaging of the entire course of the nerve from its nucleus to the end organ in order to identify a cause. MRI with and without intravenous contrast is often the modality of choice with CT playing a complementary role. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer-reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances in which peer-reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

The anterolateral cervicoatlantooccipital plexus: A novel finding with application to skull base and spine surgery and pain disorders of the head and neck

INTRODUCTION

A novel nerve plexus of the upper neck is described. By exploring how the individual components of this specific anterolateral nerve plexus communicate with each other, patient care may be improved in regard to preoperative diagnosis, intraoperative navigation, and minimally invasive treatments.

MATERIALS AND METHODS

Using a surgical microscope, 11 adult cadaveric heads (22 sides) were dissected. The region of the junction between the atlantooccipital and craniocervical junctions was explored, specifically, the innervation of this region via adjacent nerve connections. Branches from these regional nerve sources were analyzed for interconnections and when found, these branches were documented and measured.

RESULTS

A delicate nerve plexus was found overlying the anterolateral C1-C2 junction in all specimens. The plexus was contributed by the sympathetic trunk, vagus nerve, hypoglossal nerve, and C1 and C2 ventral rami. We termed this plexus the anterolateral cervicoatlantooccipital plexus (ALCAO plexus). On all but two sides (91%), the C2 ventral ramus provided the most input into the plexus with 1 to 2 branches. On two sides, the C1 ventral ramus was the primary contribution and on average, this nerve contributed 1 to 2 branches to the plexus. Interestingly, on eight sides (36.4%), the C1 fibers that are known to travel with the hypoglossal nerve and to be distributed to the geniohyoid and thyrohyoid muscles arose from C1 nerve fibers that first traversed the ALCAO plexus. The sympathetic trunk contributed 1 to 4 lateral branches with the majority of these arising superiorly from the superior cervical ganglion. The vagus nerve contributed 1-2 lateral branches and the hypoglossal nerve contributed 1 to 2 anteromedial branches. This plexus was located more or less lateral to the sympathetic trunk and superior cervical ganglion and medial to the transverse process of C1 and C2. The plexus innervated the rectus capitis lateralis, rectus capitis anterior, lateral atlantooccipital joint and on four sides, the atlantoaxial joint. Additionally, small branches were seen traveling to the anterior atlantoaxial and anterior atlantooccipital membranes on 55% and 77.2% of sides, respectively. On six sides, very small branches from the ALCAO plexus ended in the periosteum over the anterolateral aspect of the anterior arch and transverse process of the C1 vertebra.

CONCLUSION

It is important to recognize that the course of these interneural connections are variable and may pose unforeseen complications during surgical procedures. A comprehensive knowledge of these neural connections is useful when surgery and pathology of the neck and skull base are considered.

Rehabilitation of Sport-Related Concussion

This article provides a summary of clinical assessment methods and nonpharmacologic rehabilitation techniques used for concussed patients. It describes concussion-relevant physical examination methods to identify underlying symptom generators. This approach allows practitioners to prescribe targeted rehabilitation therapies to treat postconcussion symptoms. Evidence-based rehabilitation approaches include cervical rehabilitation, vestibulo-ocular rehabilitation, and sub-symptom threshold aerobic exercise.

Isolated Hypoglossal Nerve Palsy Due to an Osteophyte with Atlantoaxial Dislocation

Isolated hypoglossal nerve palsy (IHP), or hypoglossal nerve palsy without any other neurological signs, is rare. We report a woman with atlantoaxial dislocation (AAD) who presented with IHP due to hypoglossal nerve compression by an osteophyte at the hypoglossal canal. A 77-year-old woman presented with speech difficulties and the feeling of a swollen tongue on the left side for 3 days. Her only neurological feature was left hypoglossal nerve palsy. She had been diagnosed with AAD 2 years before. Computed tomography (CT) and high-resolution magnetic resonance imaging (MRI) revealed the compression of the basicranial hypoglossal nerve at the external orifice of the hypoglossal canal by an AAD osteophyte which was causing IHP. IHP can develop due to hypoglossal nerve compression by an osteophyte from AAD. CT and high-resolution MRI revealed this rare mechanism of IHP.

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.