Intracranial Connections of the Vertebral Venous Plexus: Anatomical Study with Application to Neurosurgical and Endovascular Procedures at the Craniocervical Junction.

BACKGROUND: Descriptions of intracranial extensions of vertebral venous plexuses are lacking. OBJECTIVE: To identify vertebral venous plexuses at the craniocervical junction in cadavers and describe them. METHODS: The authors dissected 15 ink-injected, formalin-fixed, adult cadaveric heads and measured cranial extensions of the spinal venous plexuses. RESULTS: All specimens had vertebral venous plexuses at the craniocervical junction composed of multiple interwoven vessels concentrated anteriorly (anterior vertebral plexuses), posteriorly (posterior vertebral venous plexuses), and laterally (lateral vertebral venous plexuses). Veins making up the plexus tended to be largest for the anterior internal vertebral venous plexus. On 33%, a previously unnamed lateral internal vertebral venous plexus was identified that connected to the lateral marginal sinus. The anterior external vertebral venous plexus connected to the basilar venous plexus via transclival emissary veins in 13%; remaining veins connected either intracranially via small perforating branches through the anterior atlanto-occipital membrane (33%) or had no direct gross connections inside the cranium (53%). The anterior internal vertebral plexus, which traveled between layers of the posterior longitudinal ligament, connected to the anterior half of the marginal sinus in 33% and anterolateral parts of the marginal sinus in 20%. The posterior internal venous plexus connected to the posterior aspect of the marginal sinus on 80% and into the occipital sinus in 13.3%. The posterior external venous plexus connected to veins of the hypoglossal canal in 20% and into the posterior aspect of the marginal sinus in 13.3%. CONCLUSION: Knowledge of these connections is useful to neurosurgeons and interventional radiologists.

Anterior Inferior Cerebellar Arteries Juxtaposed with the Internal Acoustic Meatus and Their Relationship to the Cranial Nerve VII/VIII Complex.

Vascular loops in the cerebellopontine angle (CPA) and their relationship to cranial nerves have been used to explain neurological symptoms. The anterior inferior cerebellar artery (AICA) has variable branches producing vascular loops that can compress the facial cranial nerve (CN) VII and vestibulocochlear (CN VIII) nerves. AICA compression of the facial-vestibulocochlear nerve complex can lead to various clinical presentations, including hemifacial spasm (HFS), tinnitus, and hemiataxia. The formation of arterial loops inside or outside of the internal auditory meatus (IAM) can cause abutment or compression of CN VII and CN VIII. Twenty-five (50 sides) fresh adult cadavers underwent dissection of the cerebellopontine angle in the supine position. In regard to relationships between the AICA and the nerves of the facial/vestibulocochlear complex, 33 arteries (66%) traveled in a plane between the facial/nervus intermedius nerves and the cochlear and vestibular nerves. Five arteries (10%) traveled below the CN VII/VIII complex, six (12%) traveled posterior to the nerve complex, four (8%) formed a semi-circle around the upper half of the nerve complex, and two (4%) traveled between and partially separated the nervus intermedius and facial nerve proper. Our study found that the majority of AICA will travel in a plane between the facial/nervus intermedius nerves and the cochlear and vestibular nerves. Although the relationship between the AICA and porus acusticus and AICA and the nerves of the CN VII/VIII complex are variable, based on our findings, some themes exist. Surgeons should consider these with approaches to the cerebellopontine angle.

Endoscopic third ventriculostomy: A historical review.

BACKGROUND: Endoscopic third ventriculostomy (ETV) has become one of the most common neuroendoscopic procedures. METHODS: In this article, we will review the major milestones in the history of ETV development from its early use by Walter Dandy to the techniques currently employed with advanced technology. CONCLUSIONS: ETV has become an important technique in the armamentarium of the neurosurgeon. From a meager beginning with few applications, our knowledge of long-term outcomes has evolved. ETV has a rich history and more recently, has had a renewed interest in its use. Our current understanding of its indications is growing and is based on a century of development through trial and error.

Sagittal MRI often overestimates the degree of cerebellar tonsillar ectopia: a potential for misdiagnosis of the Chiari I malformation.

BACKGROUND: We hypothesized that by using coronal MRI, Chiari I malformation could be more precisely diagnosed, would provide simple anatomic landmarks, would provide information regarding asymmetry of hindbrain herniation, and would be a better method for analyzing the tonsillar herniation postoperatively when the opisthion has been removed. METHODS: Fifty consecutive pediatric patients diagnosed with Chiari I malformation had comparison between the measurements of their caudally descended cerebellar tonsils on midsagittal and coronal MRI images. RESULTS: On MRI coronal imaging, tonsillar asymmetry was found in 48 patients. Maximal left tonsillar descent was 20.9 mm, and maximal right tonsillar descent was 17.4 mm. On MRI sagittal imaging, tonsillar descent ranged from 5 to 27.4 mm. Fifty-eight % of patients had syringomyelia. Five patients (10 %) on coronal MRI were found to have both cerebellar tonsils that were less than 3 mm below the foramen magnum. However, all of these patients had greater than 3 mm of tonsillar ectopia on sagittal imaging. Nineteen patients (38 %) on coronal MRI were found to have one of the cerebellar tonsils that were less than 3 mm below the foramen magnum. Similarly, each of these had greater than 3 mm of tonsillar ecotpia as measured on midsagittal MRI. Also, based on these findings, Chiari I malformation is almost always an asymmetrical tonsillar ectopia. CONCLUSIONS: Sagittal MRI overestimates the degree of tonsillar ectopia in patients with Chiari I malformation. Misdiagnosis may occur if sagittal imaging alone is used. The cerebellar tonsils are paramedian structures, and this should be kept in mind when interpreting midline sagittal MRI.

Can blockage or sacrifice of the middle meningeal artery lead to hydrocephalus?

BACKGROUND: The middle meningeal artery (MMA) is often sacrificed during neurosurgical procedures in the region of the pterion. This maneuver, herein, is hypothesized to be a potential reason for the development of postoperative hydrocephalus by injuring the vascular supply to the arachnoid granulations near the vertex of the skull, and thus disrupting their ability to allow for transfer of CSF from the subarachnoid space to the venous system. MATERIALS AND METHODS: To test this theory, the middle meningeal artery was isolated at the skull base and injected with India ink. Next, the superior sagittal sinus was opened and the arachnoid granulations inspected. RESULTS: All specimens demonstrated ink within the arachnoid granulations indicating that their blood supply is completely or at least partially via the middle meningeal artery. This finding with an illustrative case of surgical cautery of the middle meningeal artery at the skull base with subsequent development of hydrocephalus supports our hypothesis of potential role of iatrogenic MMA injury causing hydrocephalus. CONCLUSIONS: Our cadaveric study shows that the blood supply of the arachnoid granulations of the superior sagittal sinus is via the middle meningeal artery. Additional cases of postoperative hydrocephalus following middle meningeal artery sacrifice are needed to support our hypothesis.

Complications of transoral and transnasal odontoidectomy: a comprehensive review.

BACKGROUND: Odontoidectomy has been considered an effective way to treat anterior cervicomedullary compression in patients presenting with craniocervical joint anomalies. The transoral and transnasal routes have been described for anterior decompression surgery. However, to date, a comprehensive review of the complications from this procedure is lacking in the extant medical literature. Therefore, herein, we review this specific literature as a resource for surgeons. METHODS: A comprehensive review of the literature via online search engines was performed. CONCLUSION: The most reported complications for odontoidectomy are CSF leakage, postoperative craniocervical instability, velopharyngeal insufficiency, wound dehiscence, pulmonary issues, meningitis, and death. To our knowledge, this is the first comprehensive review of complications of odontoidectomy. Increased awareness of the more common complications associated with this procedure may help in the care of patients in the future.

Evolution of cerebellar tonsillar ischemia to cerebellar tonsillar cysts in the Chiari I malformation: radiological, surgical, and histological evidence.

BACKGROUND: Rare reports in the literature have documented the presence of a cyst at the tip of the cerebellar tonsil in patients with Chiari I malformation. The current study aimed to better elucidate these cysts and identify their etiology via a histological and radiologically analysis. PATIENTS AND METHODS: We prospectively reviewed all new Chiari I malformation (CM-I) patients who presented to our clinic during a 2-year period. This was a pediatric cohort made up of 340 children aged 3 to 18 years. Specifically, all patients were screened for ischemic or cystic lesions of the herniated cerebellar tonsils on MRI. RESULTS: Out of 340 patients, 2.9 % were found to have signal changes on MRI consistent with ischemia or cysts in the cerebellar tonsils. Of the 340 patients, 20 % underwent posterior fossa decompression. Of the 67 patients, cerebellar tonsillar ischemia was observed in 10.4 % and cerebellar tonsillar cysts were seen in 6 %. Four of the seven operative patients with cerebellar tonsillar ischemia and concomitant syringomyelia and three of these patients with tonsillar cysts concomitant syringomyelia and cerebellar tonsillar cysts underwent subpial dissection of some cerebellar tonsil to ensure that CSF egress from the fourth ventricle to the cervical subarachnoid space, and this transected tissue was also sent for histological analysis. Three of the four patients found to have intraoperative tonsillar cysts were noted to have tonsillar ischemic changes on preoperative imaging in this same region. For both ischemic and cystic cerebellar tonsils, histologically, the tissue demonstrated loss of Purkinje cells with concomitant Bergmann gliosis. The ischemic and cystic tissues were virtually the same, histologically. CONCLUSIONS: Based on our findings, cerebellar tonsillar ischemia and cysts in patients with CM-I can often be seen radiologically. Histologically, these ischemic and cystic tissues are the same. Moreover, we document patients where ischemic lesions progressed to cysts, radiologically. Taken together, cerebellar tonsillar ischemia and cysts are on a continuum and represent chronic compression of this herniated part of the cerebellum.

Formaldehyde exposure and its effects during pregnancy: Recommendations for laboratory attendance based on available data.

Formalin is commonly used in fixation of cadaveric specimens. Exposure to formaldehyde, a component of formalin and a known carcinogen, during gross anatomy laboratory dissection is a continuing concern for pregnant students and instructors. Since there is little literature on this specific topic, the current review was compiled in the hope of offering recommendations to pregnant students and instructors who are engaged in human anatomical dissection where formalin is used. Relevant articles were obtained through searches of PubMed and Google Scholar for the terms "formaldehyde," "pregnant," "formalin," and "exposure." A literature search was conducted for chemical information and articles about exposure as issued by government regulatory agencies and chemical companies that produce formaldehyde. This led to the compilation of 29 articles each of which included references to previous, relevant, human research. The reviewed literature contains data strongly suggesting that pregnancy can be affected by formaldehyde exposure. Therefore, on the basis our analysis, female students who might be pregnant should avoid formaldehyde exposure, including that in a gross anatomy laboratory. Instructors should find other means of ensuring anatomical competence for these students.

Skull base connections between the middle meningeal and internal carotid arteries.

BACKGROUND: External to internal carotid artery anastomoses are normally found in man. However, such connections at the skull base between the cavernous internal carotid artery and middle meningeal artery are rarely discussed in the literature and when present, are difficult, if not impossible, to see with imaging studies unless pathologically enlarged. Therefore, the aim of the present anatomic study was to investigate such connections via cadaveric dissection. MATERIALS AND METHODS: In 12 latex-injected adult cadaveric heads (24 sides), microdissection was performed to investigate for connections at the skull base between the cavernous part of the internal carotid and middle meningeal arteries. Additionally, neck dissections were performed to observe for atherosclerosis of the internal carotid artery. Statistical analyses were performed for differences between sides and gender. RESULTS: On 14 sides (58.3%) (nine left and five right sides), arterial anastomoses were identified between the middle meningeal and internal carotid arteries. All connections were small with a mean length of 8 mm and a mean diameter of 0.9 mm. These connections were found between the lateral aspect of the cavernous internal carotid artery and the medial side of the main trunk of the middle meningeal artery on 64.3% of sides, the anterior branch of the middle meningeal artery on 7% of sides, and the posterior branch of the middle meningeal artery on 28.6% of sides. The size of the middle meningeal and internal carotid arteries was within normal limits in all specimens. Although not statistically significant, connections tended to be more frequently found on the left sides. CONCLUSIONS: The majority of cadaveric sides in our study were found to have anastomoses at the skull base between the cavernous segment of the internal carotid and middle meningeal arteries. These very small connections would most likely not be visualized on imaging studies. These connections most likely function in times of carotid artery ischemia that is chronic in nature (e.g., Moya Moya disease) and may, in the past, have been misidentified as a human rete mirabile.

A comprehensive review of the sub-axial ligaments of the vertebral column: part I anatomy and function.

BACKGROUND: As important as the vertebral ligaments are in maintaining the integrity of the spinal column and protecting the contents of the spinal canal, a single detailed review of their anatomy and function is missing in the literature. METHODS: A literature search using online search engines was conducted. RESULTS: Single comprehensive reviews of the spinal ligaments are not found in the extant medical literature. CONCLUSIONS: This review will be useful to those who treat patients with pathology of the spine or who interpret imaging or investigate the anatomy of the ligaments of the vertebral column.

A comprehensive review of the sub-axial ligaments of the vertebral column: part II histology and embryology.

BACKGROUND: As important as the vertebral ligaments are in maintaining the integrity of the spinal column and protecting the contents of the spinal canal, a single detailed review of their histology and embryology is missing in the literature. METHODS: A literature search using online search engines was conducted. RESULTS: Single comprehensive reviews of the histology and embryology of the spinal ligaments are not found in the extant medical literature. CONCLUSIONS: This review will be useful to those who study or treat patients with pathology of the spine.

The tragedy of syrinx.

INTRODUCTION: Today, the term "syrinx" is used by many clinicians. Most users of the term, however, are not familiar with the origin of the word. The present paper reviews the history of the word syrinx, which is based in Greek mythology. CONCLUSIONS: Many modern terms have a derivation that is based on a rich history that has often been forgotten. The myth of Syrinx lives on in modern times by the continued use of syrinx in various words such as syringomyelia and syringe.