The Accessory Nerve: A Comprehensive Review of its Anatomy, Development, Variations, Landmarks and Clinical Considerations.

INTRODUCTION: The eleventh cranial nerve, the accessory nerve, has a complex and unique anatomy and has been the subject of much debate. Herein, we review the morphology, embryology, surgical anatomy, and clinical manifestations of the accessory nerve. Included in this review, we mention variant anatomy, molecular development, histology, and imaging of the accessory nerve. CONCLUSIONS: The accessory nerve continues to be a topic of much discussion regarding its exact function and in particular to its cranial roots. Recently, various surgical procedures have been devised that repurpose the accessory nerve (e.g., lengthening procedures, contralateral neurotization procedures). Currently, we continue to learn and have much to learn about this lower cranial nerve. Anat Rec, 302:620-629, 2019. © 2018 Wiley Periodicals, Inc.

Correction to: Ventriculosubgaleal shunting-a comprehensive review and over two-decade surgical experience.

The original version of this article unfortunately contained an error.

Let's get a hand on this: Review of the clinical anatomy of "knuckle cracking".

Knuckle cracking refers to the characteristic sound produced when joints are moved or distracted, and there is considerable interest in the mechanism and the clinical associations of knuckle cracking. Different mechanisms for knuckle cracking have been proposed over a century, and some have speculated that it can lead to deleterious effects on the joints. Herein, we review the literature on the mechanism and clinical associations of knuckle cracking. There is agreement in the literature regarding the formation of a bubble as part of the mechanism of knuckle cracking; however, the process by which the bubble is formed and the source of the cracking sound is not clear. The evidence for the association of knuckle cracking and osteoarthritis comes mainly from observational studies that have failed to show an association. Fewer studies report other associations mainly through descriptive, small or cross-sectional studies. Clin. Anat. 31:942-945, 2018. © 2018 Wiley Periodicals, Inc.

Ventriculosubgaleal shunting-a comprehensive review and over two-decade surgical experience.

INTRODUCTION: The subgaleal space is the fibroareolar layer found between the galea aponeurotica and the periosteum of the scalp. Due to its elastic and absorptive capabilities, the subgaleal space can be used as a shunt to drain excess cerebrospinal fluid from the ventricles. A subgaleal shunt consists of a shunt tube with one end in the lateral ventricles while the other end is inserted into the subgaleal space of the scalp. This will allow for the collection and absorption of excess cerebrospinal fluid. Indications for ventriculosubgaleal shunting (VSG) include acute head trauma, subdural hematoma, and malignancies. DISCUSSION: VSG shunt is particularly advantageous for premature infants suffering from post-hemorrhagic hydrocephalus due to their inability to tolerate long-term management such as a ventriculoperitoneal shunt. Complications include infection and shunt blockage. In comparison with other short-term treatments of hydrocephalus, the VSG exhibits significant advantages in the drainage of excess cerebrospinal fluid. VSG shunt is associated with lower infection rates than other external ventricular drain due to the closed system of CSF drainage and lack of external tubes. CONCLUSION: This review discusses the advantages and disadvantages of the VSG shunt, as well as our personal experience with the procedure.

A comprehensive review of the clivus: anatomy, embryology, variants, pathology, and surgical approaches.

INTRODUCTION: The clivus is a bony structure formed by the fusion of the basioccipital and basispheniod bone at the sphenooccipital synchondrosis. This downward sloping structure from the dorsum sellae to the foramen magnum is derived from mesoderm and ectoderm properties. METHODS: This comprehensive review of the clivus will discuss its basic anatomy, embryology, pathological findings, and surgical implications. The clivus is an endochondral bone, formed under two processes; first, a cartilaginous base is developed, and it is secondly reabsorbed and replaced with bone. Knowledge of its embryological structure and growth of development will clarify the pathogenesis of anatomical variants and pathological findings of the clivus. CONCLUSIONS: Understanding the anatomy including proximity to anatomical structures, adjacent neurovasculature properties, and anatomical variants will aid neurosurgeons in their surgical management when treating pathological findings around the clivus.

Innervation of the blood vessels of the spinal cord: a comprehensive review.

There is growing evidence that the nervous system influences spinal cord vasculature. However, most descriptions of the spinal cord have paid little attention to this important aspect. We reviewed the literature on the innervation of spinal cord vessels with an emphasis on findings that may be applicable to human medicine. Multiple neurotransmitters and competing theories have been implicated in the neural regulation of spinal cord blood vessels. Identifying valid mechanisms of pathogenesis could be beneficial to human patients with spinal cord lesions. We discuss the various findings on the neural mechanisms behind spinal cord blood flow. Further investigation is warranted due to the current emphasis on comparative animal studies without corresponding corroborative human findings.

Anatomy of the Alar Ligament: Part II: Variations of Its Attachment onto the Dens.

OBJECTIVE: Various authors have described the morphology of the alar ligaments; however, there are no reports of a cadaveric study focusing on their attachments onto the dens. The purpose of this study was to use fresh cadaveric specimens to describe in detail different attachment patterns of the alar ligaments onto the dens. METHODS: This study used 22 sides from 11 fresh frozen cadaveric heads. Specimens were obtained from 8 men and 3 women who were 67-99 years old at death. Dissection of the exact attachment of the alar ligaments onto the dens was observed from posterior, superior, and anterior views under the surgical microscope. RESULTS: From a posterior view, 6 alar ligaments passed over the tip of the dens, and 16 alar ligaments attached onto the posterolateral part of the dens; the right and left ligaments had no continuity. From a superior view, the alar ligament was classified in 2 ways: depending on the covered area of the dens (entirely or posterior two thirds) and continuity of the alar ligament (transversely, separately, or combination). Fourteen alar ligaments covered the posterior two thirds of the dens. From an anterior view, in 1 specimen, the alar ligament extended to the anterior surface of the dens. CONCLUSIONS: Wide posterolateral anchoring to the dens coupled with the nearly horizontal trajectory explains the biomechanical advantage of the alar ligaments in undertaking a stabilizing function in limiting head rotation that would otherwise be ineffective in the case of weaker attachments or a more vertical orientation.

A comprehensive review of the foramina of Luschka: history, anatomy, embryology, and surgery.

PURPOSE: The purpose of this review is to comprehensively review the foramina of Luschka in regard to their discovery, embryology, anatomy, and surgical relevance. METHODS: This subject review of the foramina of Luschka was composed after conducting a thorough review of the available literature on this topic using PubMed and other primary sources. RESULTS: The foramina of Luschka are paired apertures located in the lateral recesses of the fourth ventricle, within the posterior cranial fossa. The foramina of Luschka are of importance clinically as their blockage can disrupt the flow of cerebrospinal fluid leading to the development of hydrocephalus. These apertures were first described by the German anatomist Hubert von Luschka in the nineteenth century. These foramina are thought to emerge at around the 26th week of development. The apertures project into the cerebellopontine angle at the lateral border of the pontomedullary sulcus. CONCLUSION: The foramina of Luschka may be surgically manipulated for the excision of tumors involving the fourth ventricle and surrounding structures and accessed for cochlear nucleus stimulation.

Radiological evolution of peri-odontoid pannus in a patient with Chiari I malformation: a case-based review.

INTRODUCTION: The Chiari I malformation (CIM) is commonly encountered by neurosurgeons and can have different etiologies and clinical presentations. CASE REPORT: We report a CIM patient who presented with symptoms of ventral brain stem compression and was found to have a large peri-odontoid pannus. Posterior fossa decompression was performed with a planned second-stage odontoidectomy. However, at the 6-month follow-up, postoperative images demonstrated a mostly resolved pannus and improvement of the brain stem compression symptoms, and the patient progressed uneventfully without the need for odontoidectomy. CONCLUSIONS: This case illustrates the resolution of a significant and symptomatic peri-odontoid pannus in a patient with CIM without craniocervical fusion or odontoidectomy. Such a case indicates that not all peri-odontoid pannus formations in CIM patients are due to hypermobility at the craniocervical junction.

Cervical Spine Aneurysmal Bone Cysts in the Pediatric Population: A Systematic Review of the Literature.

Cervical spine aneurysmal bone cysts (ABCs) in pediatric patients have not been thoroughly studied. Using PubMed and Google Scholar, a systematic review of the literature was conducted for publications that included patients aged ≤15 years with a confirmed diagnosis of ABC in the cervical spine. Thirty-five studies with a total of 71 patients met the inclusion criteria. Nearly 80% of patients presented with neck or shoulder pain. The axis was the level most frequently involved (34.28%), followed by C5 (24.28%). Posterior elements were most likely to be affected (88.46%) while exclusive involvement of the body was uncommon. To our knowledge, this is the first systematic review of the literature regarding ABCs of the cervical spine in a pediatric population. Spinal ABCs are rarely found in the cervical region, and their treatment remains challenging due to their location, vascularization, and a high overall recurrence rate even with surgical resection.

Aortic arch origin of the left vertebral artery: An Anatomical and Radiological Study with Significance for Avoiding Complications with Anterior Approaches to the Cervical Spine.

Complications from anterior approaches to the cervical spine are uncommon with normal anatomy. However, variant anatomy might predispose one to an increased incidence of injury during such procedures. We hypothesized that left vertebral arteries that arise from the aortic arch instead of the subclavian artery might take a more medial path in their ascent making them more susceptible to iatrogenic injury. Fifty human adult cadavers were examined for left vertebral arteries having an aortic arch origin and these were dissected along their entire cervical course. Additionally, two radiological databases of CTA and arteriography procedures were retrospectively examined for cases of aberrant left vertebral artery origin from the aortic arch over a two-year period. Two cadaveric specimens (4%) were found to have a left vertebral artery arising from the aortic arch. The retrospective radiological database analysis identified 13 cases (0.87%) of left vertebral artery origin from the aortic arch. Of all cases, vertebral arteries that arose from the aortic arch were much more likely to not only have a more medial course (especially their preforaminal segment) over the cervical vertebral bodies but also to enter a transverse foramen that was more cranially located than the normal C6 entrance of the vertebral artery. Spine surgeons who approach the anterior cervical spine should be aware that an aortic origin of the left vertebral artery is likely to be closer to the midline and less protected above the C6 vertebral level. Clin. Anat. 30:811-816, 2017. © 2017Wiley Periodicals, Inc.

Extraforaminal compression of the L5 nerve: An anatomical study with application to failed posterior decompressive procedures.

This anatomical study was performed to elucidate the pertinent foraminal and lateral L5 nerve anatomy to enhance our understanding of possible neurologic causes of failed decompression surgery. Persistent extraforaminal L5 nerve compression is a possible cause of persistent symptoms following lumbosacral surgery. The amount of extraforaminal space for the L5 ventral ramus was examined in fifty adult human skeletons (100 sides). Based on morphology, the specimens were then categorized (types I-IV) on the basis of the bony space available for the nerve at this location. Next, 25 embalmed adult cadavers (50 sides) underwent bilateral dissection of the lower lateral lumbar region. The type of bony extraforaminal outlet was documented for each cadaver on the basis of our skeletal analysis. Lastly, segments (intra- and extra-foraminal) of the L5 ventral ramus were excised and examined histologically. Types I-IV outlets were found in 43, 31, 20 and 6 skeletal sides, respectively. For cadavers, 22,15, 10 and 3 sides were found to have types I-IV bony outlets, respectively. In cadavers, all type IV outlets and 70% of the type III bony configurations adjacent to the L5 ventral ramus had signs of neural irritation/injury including vascular hyalinization and increased fibrosis distal to the intervertebral foramen. No distal segments of type I and type II outlets showed histological signs of neural compromise. Patients with symptoms referable to L5 nerve compression for whom no proximal pathology is identified could warrant investigation of the more distal extraforaminal segment of this nerve.

The blood supply to the sacrotuberous ligament.

Knowledge of the vascular supply associated with the sacrotuberous ligament is incomplete, and at most attributed to a single coccygeal branch. Our aim was to investigate the sacrotuberous ligament vasculature with a focus on its origin and distribution. We dissected 21 hemipelvises (10 male and 11 female). The gluteus maximus was reflected medially, and a special emphasis was placed on the dissection of the vascular and neuronal structures. All specimens exhibited several (1-4) coccygeal arteries branching from the inferior gluteal artery penetrating the sacrotuberous ligament along its length. Seven specimens demonstrated the superior gluteal artery supplying sacral branches to the proximal superior border of the sacrotuberous ligament. Our study highlights several branches from a variety of origins as the supply to sacrotuberous ligament unlike previous reports stating only one vessel. Our results implicate surgical procedures in and around the area of the gluteal region such as decompressive procedures of the pudendal nerve, as it travels between the sacrotuberous and sacrospinous ligaments.

Leonardo da Vinci (1452-1519) and his depictions of the human spine.

INTRODUCTION: Few individuals in history have exerted so great an influence and made such extensive contributions to so many disciplines as Leonardo da Vinci. Da Vinci's inquisitive, experimental mentality led him to many discoveries, such as spinal cord function and the proper anatomy of several organ systems. Respected not only as an artist but also as an anatomist, he made many significant contributions to the field. CONCLUSIONS: This article explores da Vinci's drawings, in relation to the anatomy of the human spine.

Pediatric Hangman's Fracture: A Comprehensive Review.

PURPOSE: Over 170 years ago, traumatic spondylolisthesis of the axis or hangman's fracture was described. Most descriptions of this entity have focused on adult presentations. METHODS: We review the literature on pediatric cases of hangman's fracture emphasizing the embryological as well as presentation aspects. RESULTS: The majority of cervical spine fractures in children occur at C1 and C2 vertebrae. A normal anterolisthesis of C2 can be seen in younger children and can mimic the anterolisthesis seen after traumatic spondylolisthesis. CONCLUSIONS: Traumatic spondylolisthesis of the axis in children requires further investigation due to the current emphasis in the literature on adult clinical findings and diagnostic challenges from the developmental immaturity of the pediatric skeleton.

Historical Perspective of Split Cord Malformations: A Tale of Two Cords.

INTRODUCTION: Our appreciation and understanding of what is now known as the split cord malformation (SCM) have a long history. The oldest known example of SCM is from roughly AD 100. Other isolated examples can be found in the large body of work of the pathologists of the 1800s, where the SCMs were found incidentally during autopsies. CONCLUSIONS: SCM has a rich history and has intrigued physicians for over 200 years. Many well-known figures from the past such as Chiari and von Recklinghausen, both pathologists, made early postmortem descriptions of SCM. With the advent of MRI, these pathological embryological derailments can now often be detected and appreciated early and during life. Our understanding and ability to treat these congenital malformations as well as the terminology used to describe them have changed over the last several decades.