Anatomy of the craniocervical junction - A review.

An in-depth understanding of the anatomy of the craniocervical junction (CCJ) is indispensable in skull base neurosurgery. In this paper, we discuss the osteology of the occipital bone, the atlas (C1) and axis (C2), the ligaments and the muscle anatomy of the CCJ region and their relationships with the vertebral artery. We will also discuss the trajectory of the vertebral artery and review the anatomy of the jugular foramen and lower cranial nerves (IX to XII). The most important surgical approaches to the CCJ, including the far lateral approach, the anterolateral approach of Bernard George and the endoscopic endonasal approach, will be discussed to review the surgical anatomy.

Comparison of the study performance of dental students in different subfields of neuroanatomy at the Charité - Universitätsmedizin Berlin and evaluation of the neuroanatomy course in the fourth preclinical semester.

INTRODUCTION: The dentist's main working area is the head and neck region, which is innervated by the cranial nerves. On a daily basis, dentists must administer local anaesthesia to ensure pain-free treatment and differentiate between dental pain and neuropathies to avoid mistreatment. Therefore, neuroanatomical training, especially on the cranial nerves, is of immense importance for clinical practice. In order to adopt the curriculum, it is essential to constantly evaluate the quality of the training and to investigate whether there is a correlation between the students' performance and the relevance of the subfields to their work. MATERIAL AND METHODS: To address this issue, the results of MC exams in the neuroanatomy course for dental students at Charité-Universitätsmedizin Berlin from winter semester 2014/2015 to winter semester 2019/2020 were analysed. Each question was assigned to a specific subfield of neuroanatomy. We then compared cranial nerves and cranial nerve nuclei (clinically relevant) with the remaining subfields (clinically less/not relevant) to investigate whether students performed better in anatomy subfields that are more aligned with the clinical practice of a dentist. We also conducted an anonymous survey (n=201) of the dental students. RESULTS: From winter semester 2014/2015 to winter semester 2019/2020, students performed significantly (***, p< 0.001) better on the clinically relevant questions of the MC examination than on the less/not clinically relevant questions. However, when looking at each of the eleven semesters separately, only three semesters actually performed significantly better on the clinically relevant questions. Our survey also showed that students perceived the subfield of cranial nerves and cranial nerve nuclei to be the most relevant and studied it more intensively out of their own interest. DISCUSSION: The study showed that students perceived the subfield of cranial nerves and cranial nerve nuclei to be the most relevant. However, there was no direct correlation between student performance and clinically relevant questions. Using student performance alone as an indicator of relevance is not optimal, as factors such as motivation to learn can have a significant impact. CONCLUSION: Greater clinical relevance influences what students learn more intensively out of their own interest, but does not influence the results of the MC examination in favour of the subspecialty. Based on the available evidence, it is recommended that the structure of the neuroanatomy course be reconsidered.

MRI sequence optimisation methods to identify cranial nerve course for radiotherapy planning.

INTRODUCTION: Magnetic resonance imaging (MRI) is being increasingly used to improve radiation therapy planning by allowing visualisation of organs at risk that cannot be well-defined on computed tomography (CT). Diagnostic sequences are increasingly being adapted for radiation therapy planning, such as the use of heavily T2-weighted 3D SPACE (Sampling Perfection with Application optimised Contrasts using different flip angle Evolution) sequence for cranial nerve identification in head and neck tumour treatment planning. METHODS: A 3D isotropic T2 SPACE sequence used for cranial nerve identification was adapted for radiation therapy purposes. Distortion was minimised using a spin-echo-based sequence, 3D distortion correction, isocentre scanning and an increased readout bandwidth. Radiation therapy positioning was accounted for by utilising two small flex, 4-channel coils. The protocol was validated for cranial nerve identification in clinical applications and distortion minimisation using an MRI QA phantom. RESULTS: Normal anatomy of the cranial nerves CI-CIX, were presented, along with a selection of clinical applications and abnormal anatomy. The usefulness of cranial nerve identification is discussed for several case studies, particularly in proximity to tumours extending into the base of skull region. In-house testing validated that higher bandwidths of 600 Hz resulted in minimal displacement well below 1 mm. CONCLUSION: The use of MRI for radiation therapy planning allows for greater individualisation and prediction of patient outcomes. Dose reduction to cranial nerves can decrease late side effects such as cranial neuropathy. In addition to current applications, future directions include further applications of this technology for radiation therapy treatments.

Skull base dural reflection models: tool for teaching neuroanatomy at resource-scarce centers.

Skull base dural reflections are complex, and along with various ligaments joining sutures of the skull base, are related to most important vessels like internal carotid arteries (ICA), vertebral arteries, jugular veins, cavernous sinus, and cranial nerves which make surgical approaches difficult and need thorough knowledge and anatomy for a safe dissection and satisfactory patient outcomes. Cadaver dissection is much more important for the training of skull base anatomy in comparison to any other subspecialty of neurosurgery; however, such facilities are not available at most of the training institutes, more so in low- and middle-income countries (LMICs). A glue gun (100-Watt glue gun, ApTech Deals, Delhi, India) was used to spread glue over the superior surface of the bone of the skull base over desired area (anterior, middle, or lateral skull base). Once glue was spread over the desired surface uniformly, it was cooled under running tap water and the glue layer was separated from the skull base. Various neurovascular impressions were colored for ease of depiction and teaching. Visual neuroanatomy of the inferior surface of dural reflections of the skull base is important for understanding neurovascular orientations of various structures entering or exiting the skull base. It was readily available, reproducible, and simple for teaching neuroanatomy to the trainees of neurosurgery. Skull base dural reflections made up of glue are an inexpensive, reproducible item that may be used for teaching neuroanatomy. It may be useful for trainees and young neurosurgeons, especially at resource-scarce healthcare facilities.

Glossopharyngeal, Vagus and Accessory Nerves: Anatomy and Pathology.

The glossopharyngeal, vagus, and accessory nerves are discussed in this article, given their intimate anatomical and functional associations. Abnormalities of these lower cranial nerves may be intrinsic or extrinsic due to various disease processes. This article aims to review these nerves' anatomy and demonstrates the imaging aspect of the diseases which most commonly affect them.

Exceptional fossil preservation and evolution of the ray-finned fish brain.

Brain anatomy provides key evidence for the relationships between ray-finned fishes1, but two major limitations obscure our understanding of neuroanatomical evolution in this major vertebrate group. First, the deepest branching living lineages are separated from the group's common ancestor by hundreds of millions of years, with indications that aspects of their brain morphology-like other aspects of their anatomy2,3-are specialized relative to primitive conditions. Second, there are no direct constraints on brain morphology in the earliest ray-finned fishes beyond the coarse picture provided by cranial endocasts: natural or virtual infillings of void spaces within the skull4-8. Here we report brain and cranial nerve soft-tissue preservation in Coccocephalus wildi, an approximately 319-million-year-old ray-finned fish. This example of a well-preserved vertebrate brain provides a window into neural anatomy deep within ray-finned fish phylogeny. Coccocephalus indicates a more complicated pattern of brain evolution than suggested by living species alone, highlighting cladistian apomorphies1 and providing temporal constraints on the origin of traits uniting all extant ray-finned fishes1,9. Our findings, along with a growing set of studies in other animal groups10-12, point to the importance of ancient soft tissue preservation in understanding the deep evolutionary assembly of major anatomical systems outside of the narrow subset of skeletal tissues13-15.

Cranial Nerve Anatomy.

The 12 cranial nerves (CNs) all have important functions. All, except the accessory nerve, arise solely within the cranial vault. We will discuss each CN function along with its entire CN course. The modality of choice for evaluation of the CN itself is typically MRI, however, CT is very important to access the bony foramina and CN boundaries..

[Surgical Anatomy of the Cavernous Sinus, Parasellar Region, and Orbit].

The cavernous sinus, para-sellar region, and orbit have intricately intertwined cranial nerves, blood vessels, and dura mater. In surgery, anatomical understanding is very important. Recognizing the location(depth)of the cranial nerves running on the lateral and upper wall of the cavernous sinus is vital and is directly linked to postoperative complications. In addition, understanding the dural ring in the clinoid segment of the internal carotid artery is important. The periosteum on the upper surface of the anterior clinoid is the distal dural ring of the internal carotid artery, and the periosteum on the lower surface is the proximal dural ring. The orbit is filled with adipose tissue and is completely different from other intracranial parts. However, understanding the anatomy from the orbital apex to the superior orbital fissure is important in the pterional approach.

Cranial Nerve Anatomy Using a Modular and Multimodal Radiologic Approach.

Introduction: Medical students often struggle with learning cranial nerve anatomy. Typically, cranial nerve anatomy is taught using didactic lectures and textbook illustrations, often leaving students frustrated. Methods: We developed a multimodal radiologic approach to teaching cranial nerve anatomy. First, 150 students were presented with carefully curated preclass material from which to prepare. Next, they received a didactic lecture that was recorded for them to revisit on their own time. Last, students worked in groups in a lab setting with expert radiologists to identify the cranial nerves and related anatomy and learn about some basic pathophysiology. We used a pretest and posttest to examine the effectiveness of our teaching methods and a survey to measure students' satisfaction. Results: Student knowledge of cranial nerve structure was significantly improved after our module, with quiz scores increasing from 4.6 to 6.8 out of 9.0 (p < .001). In addition, students reported feeling more confident in their knowledge of the material and offered high satisfaction scores. Discussion: The breadth of knowledge covered during the preclinical training years continues to expand despite stable or even contracted durations of training, requiring knowledge to be delivered in an ever more efficient manner. Ultimately, the multimodal pedagogy used by our resource leads to students who are more confident and engaged in their learning, resulting in increased knowledge.

A three-dimensional analysis of the development of cranial nerves in human embryos.

To increase our understanding of the etiology of specific neurological disorders (e.g., Duane syndrome, glossoptosis in Pierre Robin sequence), proper knowledge of anatomy and embryology of cranial nerves is necessary. We investigated cranial nerve development, studied histological sections of human embryos, and quantitatively analyzed the 3D reconstructions. A total of 28 sectioned and histologically stained human embryos (Carnegie stage [CS] 10 to 23 [21-60 days of development]) were completely digitalized by manual annotation using Amira software. Two specimens per stage were analyzed. Moreover, quantitative volume measurements were performed to assess relative growth of the cranial nerves. A chronologic overview of the morphologic development of each of the 12 cranial nerves, from neural tube to target organ, was provided. Most cranial nerves start developing at CS 12 to 13 (26-32 days of development) and will reach their target organ in stage 17 to 18 (41-46 days). In comparison to the rest of the developing brain, a trend could be identified in which relative growth of the cranial nerves increases at early stages, peaks at CS 17 and slowly decreases afterwards. The development of cranial nerves in human embryos is presented in a comprehensive 3D fashion. An interactive 3D-PDF is provided to illuminate the development of the cranial nerves in human embryos for educational purposes. This is the first time that volume measurements of cranial nerves in the human embryonic period have been presented.

The neuroanatomy of Zulmasuchus querejazus (Crocodylomorpha, Sebecidae) and its implications for the paleoecology of sebecosuchians.

The endocranial structures of the sebecid crocodylomorph Zulmasuchus querejazus (MHNC 6672) from the Lower Paleocene of Bolivia are described in this article. Using computed tomography scanning, the cranial endocast, associated nerves and arteries, endosseous labyrinths, and cranial pneumatization are reconstructed and compared with those of extant and fossil crocodylomorphs, representative of different ecomorphological adaptations. Z. querejazus exhibits an unusual flexure of the brain, pericerebral spines, semicircular canals with a narrow diameter, as well as enlarged pharyngotympanic sinuses. First, those structures allow to estimate the alert head posture and hearing capabilities of Zulmasuchus. Then, functional comparisons are proposed between this purportedly terrestrial taxon, semi-aquatic, and aquatic forms (extant crocodylians, thalattosuchians, and dyrosaurids). The narrow diameter of the semicircular canals but expanded morphology of the endosseous labyrinths and the enlarged pneumatization of the skull compared to other forms indeed tend to indicate a terrestrial lifestyle for Zulmasuchus. Our results highlight the need to gather new data, especially from altirostral forms in order to further our understanding of the evolution of endocranial structures in crocodylomorphs with different ecomorphological adaptations.

Comparative anatomical studies on the cranial nerves of the fully formed embryos of the Nile tilapia Oreochromis niloticus (Ostiechthyes-Cichlidae). I. Nervus glossopharyngeus / Estudos anatômicos comparativos dos nervos cranianos de embriões totalmente formados da tilápia do Nilo Oreochromis niloticus (Ostiechthyes Cichlidae). I. Nervus glossopharyngeus

The organization of the roots, ganglia and the peripheral distribution of the cranial nerves of the fully formed embryos of Oreochromis niloticus are examined in the transverse serial sections. These nerves carry fibers, which were also analyzed. The results of this study demonstrated that the glossopharyngeal nerve originates by means of only one root, which leaves the cranium through the glossopharyngeal foramen. This nerve gives fibers (visceromotor) to the first internal and external levator arcus branchialis muscles. There is a single epibranchial (petrosal) ganglion located extracranially. Nervus glossopharyngeus has three rami; pharyngeus, pretramticus and posttrematicus. The ramus pharyngeus carries only viscerosensory fibers; general for the pharyngeal epithelium and special ones for the pseudobranch. General viscerosensory fibers are also carried by rami pretrematicus and posttrematicus for the pharyngeal epithelial lining. The special sensory fibers are carried by the ramus pretrematicus for the taste buds and by ramus posttrematicus for the gill filaments. The ramus pretrematicus also carries visceromotor fibers for the first adductor arcus branchialis and to the first obliquus ventralis muscles.

A organização das raízes, gânglios e a distribuição periférica dos nervos cranianos dos embriões totalmente formados de Oreochromis niloticus são examinados nas seções transversais seriais. Esses nervos carregam fibras, que também foram analisadas. Os resultados deste estudo demonstraram que o nervo glossofaríngeo se origina por meio de apenas uma raiz, que sai do crânio pelo forame glossofaríngeo. Este nervo fornece fibras (visceromotoras) para os primeiros músculos levantadores do arco branquial interno e externo. Existe um único gânglio epibranquial (petroso) localizado extracranialmente. Nervus glossopharyngeus tem três ramos; faríngeo, pretramticus e póstrematicus. O ramo faríngeo contém apenas fibras viscerossensoriais — gerais para o epitélio faríngeo e especiais para o pseudobrânquio. Fibras viscerossensoriais gerais também são transportadas por ramos pretrematicus e posttrematicus para o revestimento epitelial da faringe. As fibras sensoriais especiais são transportadas pelo ramus pretrematicus para as papilas gustativas e pelo ramus posttrematicus para os filamentos branquiais. O ramo pretrematicus também carrega fibras visceromotoras para o primeiro adutor arcus branchialis e para o primeiro músculo oblíquo ventral.

The Wandering Nerve: Positional Variations of the Cervical Vagus Nerve and Neurosurgical Implications.

BACKGROUND: The vagus ("wandering") nerve is the longest cranial nerve with the largest territory of innervation in the human body. Injury during various operative procedures involving the anterior or lateral neck may lead to serious complications. Per "textbook" descriptions, the cervical vagus nerve (CVN) commonly locates within the carotid sheath, in between the common carotid artery (CCA) and internal jugular vein (IJV). However, anatomic variations in its positioning may occur more often than expected and intraoperative identification may anticipate potential surgical pitfalls. METHODS: A literature review was conducted per PRISMA guidelines for all studies describing positional variations of the CVN within the carotid sheath. A rare and potentially dangerous variation, occurring in only 0.7% of all reported cases, is illustrated with a cadaveric case. RESULTS: Overall, 10 anatomic CVN variations have been described across 971 specimens. The non-textbook variations (26.5%) consist of: lateral (4.7%), anterolateral (8.7%), posteromedial (0.2%), posterior (5.8%), anterior (3.1%), medial (0.7%), and anteromedial (0.4%) to the CCA, as well as posterolateral (0.3%) and posterior (2.6%) to IJV. The "textbook" anatomic location is posterolateral to CCA (73.5%). Moreover, an increase in variability is reported on the left side (17.1%) compared with the right (11.3%). Our cadaveric dissection revealed a right-sided CVN directly medial to the CCA. CONCLUSIONS: Positional variations of the CVN occur in over 26% of patients and may add difficulty to an array of surgical procedures. Knowledge of these variations and their prevalence may aid the surgeon in conducting a more precise dissection possibly preventing significant potential adverse sequelae.

Microsurgical anatomy of the cranial nerve-centric triangles of the posterior cranial base: cadaveric and radiological anatomical study.

Tumors in the posterior fossa can be situated either dorsal and lateral, ventral and medial, or occupying both regions in relation to the cranial nerves, with the latter position being especially challenging. In an effort to organize neurovascular complexes contained within, anatomically based triangles have been proposed to serve as guiding landmarks for locating critical neurovascular structures. The objectives of this study were to: (1) provide a review of historical anatomically based vascular-centric triangles of the posterior fossa based on respective neurovascular complexes; (2) introduce a more organized alternative system of triangles with the conceptualization of a projection system from superficial to deep; and (3) propose and describe two new triangles of the posterior fossa: Petrous-Acousticofacial and Acousticofacial-Trigeminal. Five cadavers were studied. Neurovascular complexes were described with the use of anatomically guided cranial nerve-centric triangles, each of which was formed by cranial nerves, petrous bone, brainstem, tentorium, and superior petrosal vein. All triangles were measured and anatomical boundaries confirmed by neuronavigation. Two circumferential frameworks were created to correlate superficial and deep anatomy: (1) Outer circumference and (2) Inner circumference. Posterior fossa was divided into the following: (1) Superior complex-corresponds to the sub-asterional region, which was projected to the trigeminal nerve; (2) Middle complex-corresponds to the mastoid emissary vein foramen, which was projected to the facial and vestibulocochlear nerves; and (3) Inferior complex-corresponds to the posterior condylar canal, which projects to the lower cranial nerves. Neuronavigation confirmed these landmarks. Two new triangles were proposed: (1) The Petrous-Acousticofacial triangle, and (2) The Acousticofacial-Trigeminal triangle. Triangles provide a useful anatomical guide to the posterior fossa. We have introduced an organized schema, as well as proposed two new triangles, with the intent to minimize manipulation of neurovascular structures.

Gangliformis Intumescentia and Beyond: Antonio Scarpa and His Core Contribution to Neuroanatomy, Neurosurgery, and Otoneurosurgery.

Nearly 250 years ago, Antonio Scarpa became a professor of anatomy and surgery only 2 years after he graduated from the University of Padua. The young lecturer soon became one of the most renowned anatomists in Italy and a director of the Faculty of Medicine at the University of Pavia. He worked in the fields of general surgery and ophthalmology. Several anatomic structures have been named after him, mainly Scarpa fascia and Scarpa triangle. His interest in neuroanatomy was ardent, despite being occasionally neglected. Scarpa's contributions to the fields of neurosciences have been significant. He was the first to describe the round window and the secondary tympanic membrane, and he eventually focused on the auditory and olfactory organs. Notably, the vestibular ganglion is now known as Scarpa ganglion. Scarpa's magnum opus was the book Tabulae Neurologicae, in which he described the path of several cranial nerves including the vagus nerve and innervation of the heart. Since his death in 1832, Scarpa's head has been preserved at the University History Museum of the University of Pavia. In this historical vignette, we aim to describe Antonio Scarpa's troubled life and brilliant career, focusing on his core contributions to neuroanatomy, neurosurgery, and otoneurosurgery.

Lower cranial nerve syndromes: a review.

The purpose of this paper is to provide a comprehensive review encompassing the syndromes associated with the lower cranial nerves (LCNs). We will discuss the anatomy of some of these syndromes and the historical contributors after whom they were named. The LCNs can be affected individually or in combination, since the cranial nerves at this level share their courses through the jugular foramen and hypoglossal canal and the extracranial spaces. Numerous alterations affecting them have been described in the literature, but much remains to be discovered on this topic. This paper will highlight some of the subtle differences among these syndromes. Symptoms and signs that have localization value for LCN lesions include impaired speech, deglutition, sensory functions, alterations in taste, autonomic dysfunction, neuralgic pain, dysphagia, head or neck pain, cardiac or gastrointestinal compromise, and weakness of the tongue, trapezius, or sternocleidomastoid muscles. To assess the manifestations of LCN lesions correctly, precise knowledge of the anatomy and physiology of the area is required. Treatments currently used for these conditions will also be addressed here. Effective treatments are available in several such cases, but a precondition for complete recovery is a correct and swift diagnosis.

SnapShot: Orofacial Sensation.

Ophthalmic, maxillary, and mandibular branches of the trigeminal nerve provide sensory innervation to orofacial tissues. Trigeminal sensory neurons respond to a diverse array of sensory stimuli to generate distinct sensations, including thermosensation, mechanosensation, itching, and pain. These sensory neurons also detect the distinct sharpness or pungency of many foods and beverages. This SnapShot highlights the transduction ion channels critical to orofacial sensation.

A 360° Approach to the Craniovertebral Junction in a Cadaveric Laboratory Setting: Historical Insights, Current, and Future Perspectives in a Comparative Study.

BACKGROUND: We herein outline the experience matured in our equipped Cranio-Vertebral Junction Laboratory for anatomic dissection. METHODS: An extreme lateral approach (ELA) was performed on 4 fresh cadavers and submandibular approach was performed on 5. An endoscope and navigation-assisted far lateral approach (FLA) was performed in 5 injected specimens. In these specimens, a transoral approach was also performed, as well as a neuronavigation-assisted comparison between transoral and transnasal explorable distances. RESULTS: As calculated with neuronavigation, statistically significant differences both in the explored craniocaudal (P = 0.003) and lateral (P = 0.008) distances were observed between the transoral approach and endoscopic endonasal approach. In FLA, neuronavigation facilitated identification and partial removal of the occipital condyle; in one case, during endoscopic intradural exploration, tearing of the emerging roots of the 11th cranial nerve occurred. In ELA, the site where the accessory nerve pierces into the sternocleidomastoid muscle was found at a distance from the tip of the mastoid between 3 and 4 cm. CONCLUSIONS: During dissections, as in the clinical setting, endoscope and image guidance give the surgeon a constant orientation, increasing the accuracy and the safety of the approach. Nonetheless, the encumbrance of the endoscope could represent a limit in deep and narrow corridors as those running across the craniovertebral junction, especially in "oblique" FLA and ELA, in which the surgical target is often hidden by a delicate tangle of nerves and vessels. Its use appears more suitable and safer in "straight" approaches as transoral and transnasal in which there are no neurovascular structures interposed.

Anatomía radiológica de la base de cráneo y los nervios craneales parte 2: Nervios craneales / Skull base and cranial nerves radiologic anatomy part 2: Cranial nerves

Resumen: La anatomía de la base del cráneo es compleja. Numerosas estructuras neurovasculares vitales pasan a través de múltiples canales y agujeros ubicados en la base del cráneo. Con el avance de la tomografía computarizada (TC) y la resonancia magnética (RM), es posible la localización cada vez más precisa de lesiones y la evaluación de su relación con las estructuras neurovasculares adyacentes. El trayecto de los nervios craneales sigue un recorrido conocido y se transmiten a la cara y cuello por los forámenes de base de cráneo. La tomografía computada y la resonancia magnética son complementarias entre sí y, a menudo, se usan juntas para demostrar la extensión total de la enfermedad. La segunda parte de esta revisión se centra en el estudio radiológico de los nervios craneales.

Abstract: The skull base anatomy is complex. Many vital neurovascular structures course through the skull base canals and foramina. With the advancement of CT and MRI, the localization of lesions has become more precise as their relationship with adjacent neurovascular structures. There is a known course of the cranial nerves as well as their skull base exiting foramina to the head and neck. CT and MRI are complimentary modalities and are often used together to map the full extent of disease. The second article in this review focus on the radiologic study of the cranial nerves.

High-Resolution Ultrasound of Small Clinically Relevant Nerves Running Across the Posterior Triangle of the Neck.

With the advent of high-frequency ultrasound (US) transducers, new perspectives have been opened in evaluating millimetric and submillimetric nerves that, despite their dimensions, can be considered relevant in clinical practice. In the posterior triangle of the neck, the suprascapular, long thoracic, phrenic, supraclavicular, great auricular, lesser occipital, and transverse cervical nerves are amenable to US examination and the object of special interest because they may be involved in many pathologic processes or have a value as targets of advanced therapeutic procedures. The correct identification of these nerves requires a deep knowledge of local neck anatomy and the use of a complex landmarks-based approach with US. This article describes the anatomy and US technique to examine small but clinically relevant nerves of the posterior triangle of the neck (excluding the brachial plexus), reviewing the main pathologic conditions in which they may be involved.