Update on the Biomechanics of the Craniocervical Junction-Part I: Transverse Atlantal Ligament in the Elderly.

STUDY DESIGN: In vitro biomechanical study. OBJECTIVE: The transverse ligament is the strongest ligament of the craniocervical junction and plays a critical role in atlanto-axial stability. The goal of this cadaveric study, and the subsequent study (part II), was to reevaluate the force required for the transverse ligament and alar ligament to fail in a more physiological biomechanical model in elderly specimens. METHODS: Twelve C1-2 specimens were harvested from fresh-frozen Caucasian cadavers with a mean age at death of 81 years (range 68-89 years). Only the transverse ligament was preserved, and the bony C1-2 complex was left intact. The dens was pulled away from the anterior arch of C1 using a strength test machine that applies controlled increasing force. After testing, the axis was split in half to check for hidden pathologies and osteoporosis. The differences in the failure force between sex and age groups (group 1: <80 years, group 2: >80 years) were compared. RESULTS: The mean force required for the transverse ligament to fail was 236.2 ± 66 N (range 132-326 N). All but 2 specimens had significant osteoporotic loss of trabecular bone. No significant differences between sex and age groups were found. CONCLUSIONS: The transverse ligament's failure in elderly specimens occurred at an average force of 236 N, which was lower than that reported in the previous literature. The ligament's failure force in younger patients differs and may be similar to the findings published to date.

De novo methicillin-resistant Staphylococcus aureus vs. methicillin-sensitive Staphylococcus aureus infections of the spine, similar clinical outcome, despite more severe presentation in surgical patients.

Vertebral osteomyelitis (VO) is a severe infection of the vertebral body and the adjacent disc space, where Staphylococcus aureus is most commonly isolated. The objective of this retrospective study was to determine risk factors for and compare outcome differences between de novo methicillin-resistant Staphylococcus aureus (MRSA) VO and methicillin-sensitive Staphylococcus aureus (MSSA) VO. A retrospective cohort study was performed by review of the electronic medical records of 4541 consecutive spine surgery patients. Among these 37 underwent surgical treatment of de novo MRSA and MSSA spinal infections. Patient demographics, pre- and postoperative neurological status (ASIA impairment score), surgical treatment, inflammatory laboratory values, nutritional status, comorbidities, antibiotics, hospital stay, ICU stay, reoperation, readmission, and complications were collected. A minimum follow-up (FU) of 12 months was required. Among the 37 patients with de novo VO, 19 were MRSA and 18 were MSSA. Mean age was 52.4 and 52.9 years in the MRSA and MSSA groups, respectively. Neurological deficits were found in 53% of patients with MRSA infection and in 17% of the patients with MSSA infection, which was statistically significant (p < 0.05). Chronic renal insufficiency and malnutrition were found to be significant risk factors for MRSA VO. Preoperative albumin was significantly lower in the MRSA group (p < 0.05). Patients suffering from spinal infection with chronic renal insufficiency and malnutrition should be watched more carefully for MRSA. The MRSA group did not show a significant difference with regard to final clinical outcome despite more severe presentation.

The Petroclinoid Ligament: Its Morphometrics, Relationships, Variations, and Suggestion for New Terminology.

The anatomy and definition of the petroclinoid ligament (PCL) and its relationship with the abducens nerve are variably described. The goal of this study was to clarify the anatomy of the PCL and better elucidate its relationship with the abducens nerve. Thirty-six sides from 18 fresh-frozen adult cadaveric heads were used in this study. Specimens were all Caucasian and derived from 10 males and 8 females. The mean age at death was 79 years. Dissection of the PCL and abducens nerve was performed using a surgical microscope. The anterior and posterior attachments of the PCL, and position of the abducens nerve were noted. Subsequently, the width, thickness, and length of the ligament, and diameter of the abducens nerve were measured. Thirty-one sides (86.1%) were found to have a PCL, on two sides (5.6%), the PCL was ossified, and on three sides (8.3%), the PCL was absent. The width, thickness, and length of the PCL ranged from 0.54 to 3.39, 0.07 to 0.49, and 3.27 to 17.85 mm, respectively. No PCL had an anterior attachment onto the posterior clinoid process but rather, the clivus. Therefore, based on our findings, the PCL would be better described as the petroclival ligament.

Intraluminal anatomy of the transverse sinus: implications for endovascular therapy.

Trabeculae or septations in the transverse sinus can have potentially life-threatening clinical significance. The current study demonstrates trabecula/septum patterning within the transverse sinus with measurements and distribution data supplemented by imaging, and describes the possible etiology of idiopathic intracranial hypertension and turbulent blood flow in the transverse sinus. Twenty-four sides from 12 cadaveric heads, all fresh-frozen, were used (five males, seven females; age at death 65-91 years, mean 79.1 years). The length and diameter of the transverse sinus were measured along with the number and locations of septations/trabeculae and their tensile strength. The mean length of the transverse sinus was 68.43 mm on the right side and 74.31 mm on the left. A total of 42 septations were found in the 24 transverse sinuses. The number of septations per side ranged from zero to four with a mean of 1.75. The septations were located in the proximal 1/3 in 54.8% (23/42), the middle 1/3 in 21.4% (9/42), and the distal 1/3 in 23.8% (10/42). The work presented here furthers our understanding of transverse sinus anatomy, including its detailed internal architecture. The measurements can provide a technical guide for neurosurgeons and influence instrument selection when a large thrombus forms or anchors in one of these trabeculae or septa and necessitates treatment.

Choroidal fissure and choroidal fissure cysts: a comprehensive review.

In this paper, the authors discuss the embryology and anatomy of the choroidal fissure, as well as the pathophysiology and treatment of cerebrospinal fluid cysts of this structure. Understanding its anatomical relations to nearby structures plays an essential role during brain surgeries. With the advancement and availability of imaging techniques, lesions of the choroidal fissure are often found incidentally. Patients are usually asymptomatic or exhibit symptoms that do not correlate with anatomical location or do not require surgical treatment. The choroidal fissure is a key landmark used during brain surgery. Therefore, a comprehensive understanding of it and nearby anatomical structures is essential. Choroidal fissure cysts can be found incidentally, and well-known key features will allow one to differentiate them from other lesions. Surgical treatment should be reserved for symptomatic patients while asymptomatic patients should be monitored.

The falciform ligament: Anatomical study with microsurgical implications.

OBJECTIVES: The current study aims to increase awareness of the falciform ligament and its anatomical and surgical relationships, for the benefit of the neurosurgeon. PATINENTS AND METHODS: Twenty-four sides from twelve Caucasian cadaveric heads (all fresh-frozen) were used in this study. The length and thickness of the falciform ligament were recorded. The relationship of the falciform ligament to the optic nerve was also observed and documented. Finally, the force needed to avulse the falciform ligament was recorded. RESULTS: In all specimens, the ligament was identified as a continuation of the outer dural layer, forming a roof at the entrance of the optic canal. The mean medial-to-lateral length, anteroposterior length, and thickness of the falciform ligament were 7.97 mm, 2.12 mm, and 0.26 mm, respectively. The mean distance from the medial attachment of the ligament to the midline was 5.54 mm. For the undersurface of the falciform ligament, the optic nerve occupied the middle third in 50.0 %, the lateral third in 44.4 %, and the medial third in 5.6 % of sides. The mean optic nerve diameter at the entrance of the optic canal was 4.20 mm. The mean failure force was 2.47 N. CONCLUSION: The anatomical measurements and relationships provided in this description of the falciform ligament serve as a tool for surgery selection and planning, as well as an aid to improving microsurgical techniques, with the final goal being better patient outcomes.

Case Report of a Pelvic Crossed Fused Renal Ectopic Kidney.

Herein we present a case of a horseshoe kidney with crossed fused renal ectopia. Both of these pathologies are congenital anomalies; however, to date, there are few cases that present with both. In this case, discovered during routine dissection, the fused kidney was mostly left-sided and very low in the pelvis. No renal artery arose from the right wall of the abdominal aorta, and the right renal vein drained into the lower part of the inferior vena cava (IVC) where the right and left common iliac veins joined. It is essential for clinicians and surgeons to understand these types of congenital anomalies, as they could impact patient care.

An Anatomical Feasibility Study Using a Great Auricular Nerve Graft for Ipsilateral Inferior Alveolar Nerve Repair.

The great auricular nerve (GAN) has been used for trigeminal and facial nerve repair and the inferior alveolar nerve (IAN) are often sacrificed during segmental mandibulectomy. To our knowledge, only 1 case report has discussed IAN repair using GAN after segmental mandibulectomy. The goal of this study is to clarify the feasibility of using GAN for IAN repair. Eleven sides from 6 fresh frozen Caucasian cadavers were used for this study. The mean age at the time of death was 82.3 years. A submandibular skin incision was made 2 finger breadths below and parallel to the inferior border of the mandible. The GAN was identified and then the mental foramen was found via extraoral dissection. The buccal cortical bone was removed 5 mm posterior to the mental foramen to the wisdom tooth area. Next, the anteroposterior length of the window was measured. The diameter of the IAN at the first molar tooth area was measured. Finally, the GAN was cut with maximum available length to compare to the length of the window in the mandible. The anteroposterior length of the window and diameter of the IAN ranged from 23.1 to 31.2 mm and 1.2 to 2.1 mm, respectively. The length of the available GAN was longer than the ipsilateral bony window of the mandible on all sides. This study might encourage surgeons to consider a new way to treat patients who undergo segmental resection of the mandible with surgical neck dissection with injury to their IAN.

Ossification of the roof of the porus trigeminus with duplicated abducens nerve.

Ossification of parts of the intracranial dura mater is common and is generally accepted as an age-related finding. Additionally, duplication of the abducens nerve along its course to the lateral rectus muscle is a known, although uncommon anatomical variant. During routine cadaveric dissection, an ossified portion of dura mater traveling over the trigeminal nerve's entrance (porus trigeminus) into the middle cranial fossa was observed unilaterally. Ipsilaterally, a duplicated abducens nerve was also observed, with a unique foramen superolateral to the entrance of Dorello's canal. To our knowledge, there has been no existing report of a simultaneous ossified roof of the porus trigeminus with an ipsilateral duplicated abducens nerve. Herein, we discuss this case and the potential clinical and surgical applications. We believe this case report will be informative for the skull base surgeon in the diagnosis of neuralgic pain in the frontomaxillary, andibular, orbital, and external and middle ear regions.

Invasive Cryptococcal Meningitis Presenting as a Skull Base Mass in An Immunocompetent Host: A Case Report.

Introduction Encephalitis due to Cryptococcus neoformans has been seen almost exclusively in patients with severe compromise of their immune systems, such as acquired immune deficiency syndrome (AIDS). Fungal sinusitis with frank invasion through the cranial base and subsequent seeding of the central nervous system is rare, but should be considered in the differential of patients presenting with meningitis and sinus/skull base lesions even without obvious immune compromise. Improvements in diagnostic testing has increased the ability to correctly identify and new antimicrobials have allowed a condition that once carried a high morbidity and mortality to be managed with better outcomes. We present our treatment algorithm for successful management of an immunocompetent patient with extensive fungal encephalitis due to erosion through the skull base. Case Description The patient is a 59-year-old male presenting unresponsive with sphenoid mass erosive of the skull base and symptoms of meningitis and encephalitis due to C. neoformans . Magnetic resonance imaging (MRI) at presentation demonstrated extensive diencephalic invasion, and a sphenoid mass with erosion of the skull base. Lumbar puncture (LP) confirmed elevated opening pressure of 45 cm H2O, and cultures confirmed infection with C. neoformans . He underwent operative sinonasal debridement followed by placement of an external ventricular drain for management of hydrocephalus. He was treated aggressively with a combination of both intravenous (IV) amphotericin B daily and intrathecal amphotericin B via the ventriculostomy thrice weekly. By the 2nd week of treatment, patient regained consciousness. After 4 weeks of therapy, cerebrospinal fluid (CSF) cultures turned negative, and the external ventricular drain (EVD) was converted to a ventriculoperitoneal shunt (VPS) to manage chronic postinfectious hydrocephalus. We also placed a contralateral Ommaya reservoir to permit continued weekly intrathecal amphotericin B without violation of the shunt valve. With each instillation, the shunt was set to its highest setting to minimize CSF egress for 6 hours then reset to its "drainage" setting. After an additional 6 weeks of outpatient therapy, intrathecal therapy was discontinued. We continued CSF surveillance via Ommaya sampling monthly. At 9-month follow-up, he has remained clinically stable without evidence of recurrent infection. He has residual mild cognitive deficits, but is living semiindependently with his brother. Conclusions Fungal sinusitis is uncommon, especially in those without significantly compromised immune systems. Invasive fungal meningitis resulting in meningitis and encephalitis is even rarer. The condition carries high morbidity and mortality that can only be mitigated with a multidisciplinary effort by neurosurgery, otolaryngology, and infectious disease specialists. While there are no clear treatment guidelines, we present an approach that may permit longer term independent survival.

Internal Thoracic Artery to Vertebral Artery Bypass Surgery: A Cadaveric Feasibility Study.

OBJECTIVE: Posterior circulation strokes account for over one quarter of all ischemic strokes. The frequency of vertebral artery origin stenosis (VAOS) in patients with vertebrobasilar insufficiency (VBI) has been estimated to be as high 26%-32%, and VAOS is the direct cause of posterior circulation strokes in 9% of patients. This association could have a significant genetic component. This study examines the feasibility of the internal thoracic artery (ITA) as a donor vessel for revascularization in patients with VAOS. METHODS: Ten sides from 5 fresh-frozen white cadaveric necks derived from 3 women and 2 men were used in this study. The mean age of the cadavers at death was 77.2 years (range, 68-88 years). The subclavian artery, vertebral artery, and ITA were dissected. The length and diameter (proximal and distal) of the V1 segment and the length and diameter of the ITA were recorded. Finally, the ITA was transposed to the V1 segment of the vertebral artery (VA1). RESULTS: The mean length of the VA1 and its diameter at the proximal and distal parts were 35.51 and 3.69 mm, respectively. The mean length and diameter of the ITA were 26.53 and 3.27 mm, respectively. Rerouting the ITA to the VA1 was feasible without tension on all sides. CONCLUSIONS: This study indicates that the ITA is anatomically and hemodynamically an excellent option for bypass surgery in a VAOS scenario. We present convincing and reproducible data to aid neurosurgeons in choosing the procedure best suited to their patients.

The ABC's of Spinal Decompression: Pearls and Technical Notes.

OBJECTIVE: The foundation of spine surgery centers on the proper identification, decompression, and stabilization of bony and neural elements. We describe easily reproducible and reliable methods for optimal decompression and release of neural structures to alleviate symptoms and improve patients' quality of life. METHODS: Multiple spinal decompression techniques were described in procedures for which the goal of surgery was decompression alone or decompression and fusion. Eight fundamental techniques were described: inverted U-cut, J-cut, T-cut, L-cut, Z-cut, I-track cuts, C-cut, and O-cut. RESULTS: These foundational cuts may be combined, as needed, to develop an individually tailored approach to the patient's pathology. CONCLUSIONS: After properly identifying the anatomic structures, each of these techniques provides a consistent, reproducible, and efficient means to decompress the spine under various circumstances. These techniques provide surgical trainees with a framework for approaching surgical decompression.

Ectopic Pituitary Adenoma Presenting as a Clival Mass.

Pituitary adenomas are well described in the literature and are frequently observed and treated in clinical practice by neurosurgeons. On the other hand, ectopic adenomas are a diagnostic enigma; a good understanding of anatomy and radiological characteristics is crucial for the successful management of such pathologies. In this paper, we describe the case of a 77-year-old woman who presented with a clival mass invading the left cavernous sinus; we also discuss the associated diagnostic techniques, approaches, imaging options, and characteristics.

The Basal Subarachnoid Cisterns: Surgical and Anatomical Considerations.

The basal subarachnoid cisterns are expansions of the subarachnoid space and transmit cranial nerves and intracranial vessels. Providing neurosurgeons with key concepts, anatomical landmarks, and techniques can result in safer procedures and better patient outcomes. In this review, we discuss the major basal subarachnoid cisterns including their embryology, history, anatomical descriptions, and use during surgical approaches.

Neck movement during cervical transforaminal epidural injections and the position of the vertebral artery: an anatomical study.

BACKGROUND: Cervical transforaminal epidural steroid injections (CTFESIs) are sometimes performed in patients with cervical radiculopathy secondary to nerve-root compression. Neck movements for patient positioning may include rotation, flexion, and extension. As physicians performing such procedures do not move the neck for fear of injuring the vertebral artery, we performed fluoroscopy and cadaveric dissection to analyze any movement of the vertebral artery during head movement and its relation to the foramina in the setting of CTFESI. PURPOSE: To determine cervical rotational positioning for optimized vertebral artery location in the setting of cervical transforaminal epidural steroid injections. MATERIAL AND METHODS: Four sides from two Caucasian whole cadavers (all fresh-frozen) were used. Using a guide wire and digital subtraction fluoroscopy, we evaluated the vertebral artery mimicking a CTFESI, then we removed the transverse processes and evaluated the vertebral artery by direct observation. RESULTS: After performing such maneuvers, no displacement of the vertebral artery was seen throughout its course from the C6 to the C2 intervertebral foramina. To our knowledge, this is the first anatomical observation of its kind that evaluates the position of the vertebral artery inside the foramina during movement of the neck. CONCLUSION: Special caution should be given to the medial border of the intervertebral foramina when adjusting the target site and needle penetration for the injection. This is especially true for C6-C4 levels, whereas for the remaining upper vertebrae, the attention should be focused on the anterior aspect of the foramen. Since our study was centered on the vertebral artery, we do not discard the need for contrast injection and real-time digital subtraction fluoroscopy while performing the transforaminal epidural injection in order to prevent other vascular injuries.

Disaster Scenarios in Spine Surgery: A Survey Analysis.

STUDY DESIGN: Survey analysis among spine surgeons. OBJECTIVE: To identify current consensus and discrepancies in managing adverse intraoperative events among spine surgeons. SUMMARY OF BACKGROUND DATA: Major intraoperative events are not commonly the subject of formal medical training, in part due to the relative paucity of their occurrence and in part due to an insufficient evidence base. Given the clinical impact of appropriate complication management, it is important to identify where surgeons may be able to improve decision making when choosing interventions. METHODS: A survey was created including five hypothetical unpredicted scenarios affecting different organ systems to assess the respondents' preferred reactions. The five clinical vignettes that were selected by the researchers involved: 1) loss of spinal signals in neuro-monitoring, 2) prone position cardiac arrest, 3) prone position hypoxia during thoracic corpectomy and instrumentation, 4) supine cervical vertebral artery injury, and 5) sudden onset hypotension in major prone position reconstructive spine surgery. Twenty-eight surveys (Spine Fellows n = 11; Spine surgeon Faculty n = 17) were completed and returned to the investigators. Results were sorted and ranked according to the frequency each action was identified as a top five choice. RESULTS: Following formal statistical evaluation loss of signals in neuro-monitoring had the statistically significantly most uniform response while the scenario involving cardiac compromise had the most heterogeneous. Many "best" responses had near or complete consensus while some "distractor" possibilities that could harm a patient were also selected by the respondents. CONCLUSION: The heterogeneity of responses in the face of "disaster scenario" intraoperative events shows there is room for more thorough and directed education of spine surgeons during training. As surgical teaching moves toward increased use of patient simulation and situational learning, these vignettes hopefully serve to provide direction for training future spine surgeons on how best to approach difficult situations. LEVEL OF EVIDENCE: 4.

The Great Auricular Nerve: Anatomical Study with Application to Nerve Grafting Procedures.

BACKGROUND: When it comes to autogenous nerve grafting, the sural and great auricular nerve (GAN) are the 2 nerves predominately used for trigeminal and facial nerve repair. Arising from the second and third cervical ventral rami, the GAN emerges from the posterior border of the sternocleidomastoid coursing superiorly and anteriorly toward the ear. METHODS: Eleven sides from 5 Caucasian and 1 Asian cadaveric heads (all fresh-frozen) were used. One man and 5 women were used with an age at death ranging from 57 to 91 years, with a mean of 80.3 years. Measurements were made from the inferior border of the ear to the GAN, the GAN to the external jugular vein, and the inferior border of the mastoid process to the GAN; the proximal, medial, and distal diameters of the GAN and the length of the GAN that was obtained from this exposure were also measured. RESULTS: The mean distance from the inferior border of the mastoid process to the GAN, inferior border of the ear to the GAN, and GAN to the external jugular vein was 27.71, 31.03, and 13.28 mm, respectively. The mean length of the GAN was 74.86 mm. The mean diameter of its distal, middle, and proximal portions was 1.51, 1.38, and 1.58 mm, respectively. CONCLUSIONS: The GAN is an excellent option for use in nerve grafting for repair of, for example, facial dysfunction. In this study, we review our measurements, techniques for identification, and dissecting techniques for the GAN. The proximity to the operative area and minimal complications associated with GAN grafting might contribute to improved patient satisfaction and better outcomes regarding functional restoration.

Anatomic Study of the Superior Cluneal Nerve and Its Related Groove on the Iliac Crest.

OBJECTIVE: Superior cluneal nerve entrapment neuropathy is one cause of low back pain often referred to as "pseudo sciatica." Studies have found that the superior cluneal nerve can arise variably from T11 to L5. The osteofibrous tunnels formed by a groove on the iliac crest might compress the superior cluneal nerve. Therefore, the purpose of this study was to investigate the origin of the superior cluneal nerve and its course through such bony grooves. METHODS: Twenty sides from 10 fresh frozen Caucasian cadavers were used in this study. Once both the superior cluneal nerve and its groove were identified, the distance from the groove to the posterior superior iliac spine and midline was measured. RESULTS: A total of 12 grooves were identified in 11 of 20 sides (55%). On 10 sides, the nerve running on the groove was the medial branch of the superior cluneal nerve. The mean distance from the bony groove to the posterior superior iliac spine and midline was 45.2 ± 11.2 mm and 65.3 ± 8.2 mm, respectively. CONCLUSIONS: These results could help identify such bony grooves and better understand low back pain and its related anatomy.

Gerber's Ligament-A Forgotten Structure of the Craniocervical Junction.

BACKGROUND: Ligaments of the craniocervical junction play a critical role in stabilizing this region. Gerber's ligament has more or less been forgotten and, to our knowledge, never studied. METHODS: Dissection of the craniocervical junction was performed in 15 fresh frozen cadavers. In the prone position, the posterior elements of the upper cervical vertebrae and occiput were removed. After removing the contents of the spinal canal and posterior cranial fossa, the dura mater and tectorial membrane were reflected. The superior band of the cruciform ligament was reflected. When Gerber's ligament was identified, its attachments and morphometry were recorded. Lastly, Gerber's ligament was observed while range of motion of the craniocervical junction was performed. RESULTS: Gerber's ligament was identified in 7 specimens (46.7%). This structure arose anteriorly from the junction of the superior band and transverse part of the cruciform ligament. Gerber's ligament was always found to be just deep to the superior band of the cruciform ligament but traveled more anteriorly to attach onto the posterior aspect of the dens approaching, but not attaching onto, its apex. Mean length was 11 mm, and mean width was 7 mm. Thickness of the ligament was 0.5-1.1 mm. The ligament was found to become taut with minimal rotation of the atlantoaxial joint and extension of the craniocervical junction. CONCLUSIONS: A good understanding of all ligaments of the craniocervical junction is important to surgeons and physicians treating patients with injury to the upper cervical spine.

Transclival Venous Circulation: Anatomic Study.

INTRODUCTION: The clivus is a small, central area of the basal cranium with limited surgical access and high morbidity associated with pathologies of its surrounding structures. Therefore thorough knowledge and understanding of the anatomy in this region are crucial for the success of treatments and interpretation of imaging. As to our knowledge, there is no extant cadaveric examination of the transclival veins, so the present study was performed. METHODS: Fifteen lightly embalmed adult heads underwent blue latex injection of the left and right internal jugular veins. Special attention was given to the presence or absence of transclival vessels. When transclival veins were identified, their intracranial source, point of penetration of the clivus and anterior connections were documented. RESULTS: Ten (66.7%) specimens were found to have transclival veins. These connected the basilar venous plexus to the retropharyngeal venous plexus on all specimens. Eight of the 10 specimens had multiple transclival veins, and 2 had only 1 vessel. The majority of the transclival veins were found penetrating the clivus at its lower one third. However, 2 specimens also had transclival veins that pierced the clivus at its upper one third. CONCLUSIONS: An improved understanding of the skull base and its venous drainage can assist clinicians and surgeons in better understanding normal, pathologic, and variant anatomy in this region.