Extradural anterior clinoidectomy. Technical note

Microsurgical clipping of ruptured supraclinoid internal carotid artery aneurysm with extradural clinoidectomy

BACKGROUND

Supraclinoid Internal Carotid Artery (ICA) aneurysms require additional access to standard pterional craniotomy via extradural clinoidectomy. Existing texts and surgical videos lack clarity, explanation and a clear step by step process.

CASE DESCRIPTION

We present a case of a ruptured supraclinoid ICA aneurysm and extradural clinoidectomy along with 3D reconstructed imaging of the case anatomy to guide its resection. Real-time unedited on table rerupture provides an example of management.

CONCLUSION

Extradural Anterior Clinoidectomy is a key maneuver in cerebrovascular surgical armamentarium for clipping of supraclinoid aneurysms. Stereotypical Pathological or Surgical Anatomy, its application, and availability with 3D imaging should be facilitates the framing and learning of normal physiological anatomy.

Comparison of Accessibility to Cavernous Sinus Areas Throughout Endonasal, Transorbital, and Transcranial Approaches: Anatomic Study With Quantitative Analysis

BACKGROUND

The cavernous sinus (CS) is accessed through several approaches, both transcranially and endoscopically. The transorbital endoscopic approach is the newest proposed route in the literature.

OBJECTIVE

To quantify and observe the areas of the CS reach from 2 endoscopic and 1 transcranial approaches to the CS in the cadaver laboratory.

METHODS

Six CSs were dissected through endoscopic endonasal, transorbital endoscopic, and transcranial pterional approaches, with previous implanted references for neuronavigation during the dissection. Point registration was used to mark the CS exposure and limits through each approach for later area and volume quantification through a computerized technique.

RESULTS

The endoscopic endonasal approach reaches most of the CS except part of the sinus's superior, lateral, and posterior regions. The area exposed through this approach was 210 mm 2 , and the volume was 1165 mm 3 . The transcranial pterional approach reached the superior and part of the lateral sides of the sinus, not allowing good access to the medial side. The area exposed through this approach was 306 m 2 , whereas the volume was 815 m 3 . Finally, the transorbital endoscopic approach accessed the whole lateral side of the sinus but not the medial one. The area exposed was the greatest, 374 m 2 , but its volume was the smallest, 754 m 3 .

CONCLUSION

According to our results, the endonasal endoscopic approach is the direct route to access the medial, inferior, and part of the superior CS compartments. The transorbital approach is for the lateral side of the CS. Finally, the transcranial pterional approach is the one for the superior side of the CS.

Key role of microsurgical dissections on cadaveric specimens in neurosurgical training: Setting up a new research anatomical laboratory and defining neuroanatomical milestones

Introduction

Neurosurgery is one of the most complex surgical disciplines where psychomotor skills and deep anatomical and neurological knowledge find their maximum expression. A long period of preparation is necessary to acquire a solid theoretical background and technical skills, improve manual dexterity and visuospatial ability, and try and refine surgical techniques. Moreover, both studying and surgical practice are necessary to deeply understand neuroanatomy, the relationships between structures, and the three-dimensional (3D) orientation that is the core of neurosurgeons' preparation. For all these reasons, a microsurgical neuroanatomy laboratory with human cadaveric specimens results in a unique and irreplaceable training tool that allows the reproduction of patients' positions, 3D anatomy, tissues' consistencies, and step-by-step surgical procedures almost identical to the real ones.

Methods

We describe our experience in setting up a new microsurgical neuroanatomy lab (IRCCS Neuromed, Pozzilli, Italy), focusing on the development of training activity programs and microsurgical milestones useful to train the next generation of surgeons. All the required materials and instruments were listed.

Results

Six competency levels were designed according to the year of residency, with training exercises and procedures defined for each competency level: (1) soft tissue dissections, bone drilling, and microsurgical suturing; (2) basic craniotomies and neurovascular anatomy; (3) white matter dissection; (4) skull base transcranial approaches; (5) endoscopic approaches; and (6) microanastomosis. A checklist with the milestones was provided.

Discussion

Microsurgical dissection of human cadaveric specimens is the optimal way to learn and train on neuroanatomy and neurosurgical procedures before performing them safely in the operating room. We provided a “neurosurgery booklet” with progressive milestones for neurosurgical residents. This step-by-step program may improve the quality of training and guarantee equal skill acquisition across countries. We believe that more efforts should be made to create new microsurgical laboratories, popularize the importance of body donation, and establish a network between universities and laboratories to introduce a compulsory operative training program.

Innovative growth and development of a neurological surgery residency cadaveric skull base simulation training program: A single institution experience

OBJECTIVE

Neurosurgical cadaveric and simulation training is a valuable opportunity for residents and fellows to develop as neurosurgeons, further neuroanatomy knowledge, and develop decision-making and technical expertise. The authors describe the growth and development of Oregon Health & Science University (OHSU) Department of Neurological Surgery (NSG) resident hands-on simulation skull base course and provide details of course layout and setup.

METHODS

A three-part surgical simulation series was created to provide training in cadaveric skull base procedures. Course objectives were outlined for participants. Residents participated in NSG hands-on simulation courses (years 2015-2020) and completed annual course curriculum and anonymous course evaluations, which included free text reviews. Courses were evaluated by Likert scale analysis within Python, and free text was quantified using Valence Aware Dictionary for sEntiment Reasoning (VADER). Descriptive statistics were calculated and plotted using Python's Seaborn and Matplotlib library modules.

RESULTS

Analysis included 162 skull base (anterior fossa, middle fossa and lateral, and endoscopic endonasal-based) simulation course evaluations. Resident responses were overwhelmingly positive. Likert responses demonstrated high average responses for each question (4.62 ± 0.56 and above). A positive attitude about simulation courses is supported by an average compound sentiment value of 0.558 ± 0.285.

CONCLUSION

This is the first time Likert responses and sentiment analysis have been used to demonstrate how neurosurgical residents view a comprehensive, multi-year hands-on simulation training program. We hope the information presented serves as a guide for other institutions to develop their own residency educational curriculum in cadaveric skull base procedures.

Use of BoneScalpel Ultrasonic Bone Dissector in Anterior Clinoidectomy and Posterior Fossa Surgery: Technical Note

BackgroundFirst popularized by Dolenc, anterior clinoidectomies were performed with rongeurs, before the adoption of modern high-speed drills. We describe a novel application of the piezoelectric BoneScalpel™ in anterior skull base and posterior fossa surgeries. In the literature, to date, there are no mentions of anterior clinoidectomies performed with piezosurgical devices.MethodsWe reported a total of 12 patients, 8 affected by posterior fossa tumors and 4 treated for anterior skull base oncologic and vascular pathologies. This study aims to assess the safety and efficacy of the piezoelectric osteotomy in skull base and posterior fossa surgeries. In all patients, an ultrasonic bone dissector (BoneScalpel™ - Misonix) was used to perform the anterior clinoidectomy (AC) and craniotomy.ResultsA successful clinoidectomy was performed in 4 out of 12 patients (33.3%). We did not notice any heat damage to the surrounding soft tissue in critical areas such as paraclinoid structures. We documented only one durotomy in an oncologic patient, while no lesions of SSS or TS were detected.We recorded only a slightly increased surgery duration in the PIEZOSURGERY® and BoneScalpel™ group, compared to standard surgery with an osteotome to perform craniotomies, but no time difference in performing the clinoidectomy between BoneScalpel™ and a conventional high-speed drill.ConclusionWe report the first experience with piezosurgery for anterior clinoidectomy. There is no time difference in performing the clinoidectomy between BoneScalpel™ and a conventional high-speed drill, and this is an undoubted advantage in critical contexts such as clinoid-paraclinoid surgeries, where the risk of dural sinuses tears is common.

Endoscopic transorbital extradural anterior clinoidectomy: A stepwise surgical technique and case series study [SevEN-013]

Background

Anterior clinoidectomy is an important procedure for approaching the central skull base lesions. However, anterior clinoidectomy through the endoscopic transorbital approach (ETOA) still has limitations due to technical difficulties and the structural complexity of the anterior clinoid process (ACP). Therefore, the authors designed a stepwise surgical technique of extradural anterior clinoidectomy through the ETOA. The purpose of this study was to evaluate the feasibility of this technique.

Methods

Anatomical dissections were performed in 6 cadaveric specimens using a neuroendoscope and neuro-navigation system. The extradural anterior clinoidectomy through the ETOA was performed stepwise, and based on the results, this surgical technique was performed in the 7 clinical cases to evaluate its safety and efficiency.

Results

Endoscopic extradural anterior clinoidectomy was successfully performed in all cadaveric specimens and patients using the proposed technique. This 5-step technique enabled detachment of the lesser wing of sphenoid bone from the ACP, safe unroofing of the optic canal, and resection of the optic strut without injuring the optic nerve and internal carotid artery. Since the sequential resection of the 3 supporting roots of the ACP was accomplished safely, anterior clinoidectomy was then successfully performed in all clinical cases. Furthermore, no complications related to the anterior clinoidectomy occurred in any clinical case.

Conclusion

We designed a stepwise surgical technique that allows safe and efficient anterior clinoidectomy through the ETOA. Using this technique, extradural anterior clinoidectomy can be accomplished under direct endoscopic visualization with low morbidity. Since this technique is applicable to the central skull base surgery where anterior clinoidectomy is necessary, it expands the application of the ETOA.

Clipping Ophthalmic Segment Artery Aneurysms Using a Modified Subdural Dolenc Approach: Classification and Experience Sharing

BACKGROUND

Ophthalmic segment artery aneurysms (OSAs) are difficult to clip; therefore, improvement of the surgical method is of great significance to the prevention of complications, and the classification of the aneurysms is essential to formulate a reasonable surgical plan.

OBJECTIVE

To explore the strategies and effects of surgery for OSAs using a modified subdural Dolenc approach.

METHODS

The clinical data of 38 patients (12 men and 26 women, aged 48-73 years) with OSA were analyzed retrospectively. A total of 44 aneurysms were identified, 40 of which were OSAs. The 40 aneurysms were divided into types Ia1 (n = 2), Ia2 (n = 2), Ib (n = 6), IIa (n = 4), IIb (n = 4), IIIa (n = 0), IIIb (n = 4), IIIc (n = 16), and IV (n = 2) based on preoperative images. Thirty-nine OSAs were operated successfully through pterional craniotomy combined with the modified subdural Dolenc approach, and 1 aneurysm was clipped through the contralateral approach. Clinical outcomes were evaluated using the Glasgow Outcome Scale (GOS).

RESULTS

Thirty-nine OSAs were clipped, and one was wrapped. Visual dysfunction, headache, and dizziness improved after the operation in 18 patients. One patient had new visual impairment, and there were no deaths. At discharge, the GOS score was 5 in 36 cases, 4 in 1 case, and 3 in 1 case. Thirty-seven patients had a GOS score of 5, and 1 patient had a score of 3 at 6 months after the operation.

CONCLUSION

The modified subdural Dolenc approach (Zheng approach) for clipping OSAs may be associated with less trauma and good postoperative outcomes.

Premammillary artery infarction after microsurgical clipping of unruptured posterior communicating artery aneurysm: risk factors and surgical and anatomical considerations

Posterior communicating artery (PCoA) aneurysm is common and sometimes requires microsurgery; however, as data on premammillary artery (PMA) infarction after clipping is scarce, we retrospectively reviewed cases of post-clipping PMA infarction to analyze incidence, independent risk factors of infarction, and anatomical considerations. Data from 569 consecutive patients who underwent microsurgical clipping for unruptured PCoA aneurysm between January 2008 and December 2020 were included. Patients were categorized into the normal or the PMA infarction group. Statistical analyses and comparisons between the two groups were used to determine the influence of various factors. The normal group included 515 patients while the PMA infarction group had 31. The mean length of hospital stay was significantly longer in the PMA infarction group (10.3 ± 9.1 days) than in the normal group (6.5 ± 6.4 days; p < 0.0001). The distribution of Glasgow Outcome Scale at discharge was significantly different between the two groups (p ≤ 0.0001) but was not so at 6 months after discharge (p = 0.0568). Multivariate logistic regression analysis identified aneurysm size (odds ratio [OR], 1.194; 95% confidence interval [CI], 1.08-1.32; p = 0.0005) and medial direction of aneurysm (OR, 4.615; 95% CI, 1.224-17.406; p = 0.0239) as independent risk factors of post-clipping PMA infarction. Surgeons must beware of PMA infarction after clipping of large aneurysms that are medial in direction. Intraoperative verification of the patency of the PCoA and the PMA from various angles using various intraoperative methods can reduce morbidity due to PMA infarction.

The Final Cut: Evolution of Cavernous Sinus Decompression Beyond the Dolenc Cut

BACKGROUND

Meningiomas involving the cavernous sinus (CS) represent a formidable challenge to neurosurgeons. Because of high morbidity, aggressive tumor resection within the CS has been largely replaced by extracavernous tumor resection and decompression of the CS. The widely used Dolenc method involves blind dural transection over the oculomotor nerve, potentially placing the crossing trochlear nerve at risk.

OBJECTIVE

To provide a safer way for the decompression of the CS and at the same time, circumferential resection of the temporal lobe dura.

METHODS

Cadaveric dissection of 8 cadaveric heads (16 sides) was performed. Frontotemporal craniotomy with zygomatic osteotomy was performed. Extradural and intradural dissection of the lateral wall of the CS and free edge of tentorium was performed. Photographic documentation, artistic illustrations, and illustrative video cases are provided.

RESULTS

Three tether points were released: anterior-the meningo-orbital band, lateral-dura over the V2 and V3, and medial-superficial layer of the free edge of tentorium. Transection of the superficial layer of the free edge of the tentorium along its edge, in conjunction with a lateral cut over the temporal convexity, constitutes the final cut, allowing a resection of the lateral CS wall and the circumferential resection of temporal lobe dura.

CONCLUSION

Using the "final cut" technique allows for a circumferential resection of the temporal lobe dura and lateral CS wall while avoiding blind cuts that could put cranial nerves at risk. All dural transections are performed in anatomically separated layers under constant visualization.

Ophthalmic Segment Aneurysms: Surgical Treatment and Outcomes

Background  Surgical treatment of ophthalmic segment aneurysms (OSAs) remain challenging because of complex anatomy surrounding the aneurysm and entails extensive drilling of anterior clinoid process to define proximal neck of the aneurysm and carotid exposure in the neck for proximal control. Materials and Methods  Authors present a retrospective analysis of 36 aneurysms in 35 patients with OSAs operated surgically by first author. Surgical clipping was done for the aneurysms as primary modality of treatment along with wrapping and trapping as required. Results  Commonest age group was 40 to 60 years with female preponderance of 3:1. Maximum (23) patients presented with subarachnoid hemorrhage (WFNS Gr 1), followed by asymptomatic patients (six). There were 18 small, 14 large, and four giant aneurysms, 15 dorsal wall, 17 ventral wall, three proximal posterior wall, and one blister aneurysm. Good outcome, as measured by Glasgow Outcome Score (GOS) was achieved in 29 patients. Conclusion  OSAs are technically demanding aneurysms, but with due diligence to surgical principles, good outcomes may be obtained.

Extradural anterior clinoidectomy through endoscopic transorbital approach: laboratory investigation for surgical perspective

BACKGROUND

The endoscopic transorbital approach (eTOA) is a new mini-invasive procedure used to explore different areas of the skull base. Authors propose an extradural anterior clinoidectomy (AC) through this corridor, defining the anatomical landmarks of the anterior clinoid process (ACP) projection onto the posterior orbit wall and the technical feasibility of this approach. We describe the exposure of the opticocarotid region and the surgical freedom and the angles of attack obtained with this novel approach.

METHODS

Five cadaver heads underwent an eTOA at the Laboratory of Surgical Neuroanatomy of the University of Barcelona. A step-by-step description of the extradural endoscopic transorbital clinoidectomy was provided. A volumetric analysis of the morphometrics characteristics of the sphenoid wings was evaluated before and after dissection using CT scans. Pterional approach was performed to ascertain ACP removal.

RESULTS

In all the specimens, it was possible to resect the ACP endo-orbitally aiming an optimal optic canal (OC) unroofing. The surface of the triangle corresponding to the ACP projection onto the posterior orbit wall was 0.42 ± 0.20 cm². The drilled area to perform the extradural clinoidectomy via eTOA was 3.11 ± 2.27 cm², and the volume of bone removal corresponding to the greater sphenoid wing (GSW) and lesser sphenoid wing (LSW) was 2.55 ± 1.41 and 0.26 ± 0.18 cm³ respectively. The area of surgical freedom provided by the eTOA was (3.11 ± 2.27cm²), and the angles of attack were 21.39 ± 9.13° in the horizontal axel and 30.63 ± 18.51° in the vertical.

CONCLUSIONS

The described extradural anterior clinoidectomy by eTOA uses specific landmarks to localize the ACP on the posterior orbit wall. Resection of the ACP is a technically feasible approach, achieving the main goals of any clinoidectomy.

Extradural anterior clinoidectomy in surgical management of clinoidal meningiomas

Background

Despite the recent advances in skull base surgery, microsurgical techniques, and neuroimaging, yet surgical resection of clinoidal meningiomas is still a major challenge. In this study, we present our institution experience in the surgical treatment of anterior clinoidal meningiomas highlighting the role of extradural anterior clinoidectomy in improving the visual outcome and the extent of tumor resection. This is a prospective observational study conducted on 33 consecutive patients with clinoidal meningiomas. The surgical approach utilized consisted of extradural anterior clinoidectomy, optic canal deroofing with falciform ligament opening in all patients. The primary outcome assessment was visual improvement and secondary outcomes were extent of tumor resection, recurrence, and postoperative complications.

Results

The study included 5 males and 28 females with mean age 49.48 ± 11.41 years. Preoperative visual deficit was present in 30 (90.9%) patients. Optic canal involvement was present in 24 (72.7%) patients, ICA encasement was in 16 (48.5%), and cavernous sinus invasion in 8 (24.2%). Vision improved in 21 patients (70%), while 6 patients (20%) had stationary course and 1 patient (3%) suffered postoperative new visual deterioration. Gross total resection was achieved in 24 patients (72.7%). The main factors precluding total removal were cavernous sinus involvement and ICA encasement. Mortality rate was 6.1%; mean follow-up period was 27 ± 13 months.

Conclusions

In this series, the use of extradural anterior clinoidectomy provided a favorable visual outcome and improved the extent of resection in clinoidal meningioma patients.

Impact of Anterior Clinoidectomy on Visual Function After Paraclinoid Carotid Artery Aneurysm Surgery: Power-Drill Versus No-Drill Technique

BACKGROUND

Few studies have attempted to make a direct comparison of the risk of visual impairment following extradural anterior clinoidectomy (EAC) with and without the use of a power drill.

OBJECTIVE

To evaluate postoperative visual outcomes between groups of patients with paraclinoid carotid artery aneurysms (PCAAs) who underwent surgical clipping with and without the use of a power drill during EAC.

METHODS

Between January 2010 and November 2019, 90 patients, 7 with ruptured and 83 with unruptured PCAAs, underwent clipping surgery at our hospital. The authors retrospectively analyzed postoperative visual complications from the medical records of these patients.

RESULTS

Among the 85 patients (excluding 3 patients with disturbance of consciousness caused by subarachnoid hemorrhage and 2 patients with preoperative visual disturbance) evaluated, EAC was conducted using a power drill in 64 patients and using a microrongeur in 21 patients. Permanent postoperative visual impairment developed in 14 (21.9%) patients in the drill group: 9 patients had ipsilateral lower nasal quadrant hemianopsia (ILNQH) and 5 patients had ipsilateral visual acuity reduction. Transient ILNQH developed in only 1 patient in the no-drill group. The incidence of permanent postoperative visual impairments was significantly lower in the no-drill group than in the drill group (P = .020). Seventeen (26.6%) patients developed transient oculomotor nerve palsy in the drill group, while no patients developed oculomotor nerve palsy in the no-drill group.

CONCLUSION

EAC using a microrongeur versus a power drill significantly improved visual outcomes after clipping surgery for PCAAs.

Tailored Anterior Clinoidectomy: Beyond the Intradural and Extradural Concepts

Anterior clinoidectomy (AC) is a key microsurgical step for the safe and successful management of parasellar pathologies that involve the anterior clinoid process (ACP) and the optic canal. Traditionally, extra and intradural ACs are performed separately according to the surgeon's experience or preference. The objective is to present and discuss the tailored AC concept through illustrative cases. We conducted a retrospective record review of three patients who underwent AC as a surgical step for the treatment of parasellar pathologies that involve the ACP and optic canal. A review of the relevant literature on AC was performed in the PubMed, LILACS, and SciELO databases.

In all three cases, the pterional craniotomy was the preferred approach for AC. Case 1, a 47-year-old female patient with type III anterior clinoidal meningioma, underwent a tailored intradural technique (optic canal unroofing) with total tumor resection and complete visual recovery. Case 2, a 63-year-old female patient with a complex type II anterior clinoidal meningioma with extensive hyperostosis of the ACP, underwent a hybrid AC technique with complete removal of the tumor and visual improvement. Case 3, a 62-year-old female, underwent a tailored intradural AC for clipping an incidental carotid-ophthalmic aneurysm.

Tailored AC aims to provide adequate exposure with less risk of neurovascular injury, allowing enough space to safely treat parasellar lesions. The type, size, and location of the lesion, as well as the surgeon’s experience, should always be considered for surgical planning.

Arachnoid and dural reflections

The dura mater is the major gateway for accessing most extra-axial lesions and all intra-axial lesions of the central nervous system. It provides a protective barrier against external trauma, infections, and the spread of malignant cells. Knowledge of the anatomical details of dural reflections around various corners of the skull bases provides the neurosurgeon with confidence during transdural approaches. Such knowledge is indispensable for protection of neurovascular structures in the vicinity of these dural reflections. The same concept is applicable to arachnoid folds and reflections during intradural excursions to expose intra- and extra-axial lesions of the brain. Without a detailed understanding of arachnoid membranes and cisterns, the neurosurgeon cannot confidently navigate the deep corridors of the skull base while safely protecting neurovascular structures. This chapter covers the surgical anatomy of dural and arachnoid reflections applicable to microneurosurgical approaches to various regions of the skull base.

A systematic review of the surgical anatomy of the orbital apex

PURPOSE

The orbital apex is the narrowest part of the orbit, housing the link between the intracranial cavity and orbit. Knowledge of orbital apex anatomy is crucial to selecting a surgical approach and reducing the risk of complications. Our purpose is to summarize current knowledge on surgical anatomy and attempt to reach a consensus on definition of the orbital apex.

METHODS

The online databases of Embase, the Cochrane library, Web of Science and PubMed (MEDLINE) were queried in a comprehensive bibliographic search on the (surgical) anatomy of the orbital apex and consisted of a combination of two subjects, using indexed terms and free text: "Orbital Apex" and "Orbital Anatomy."

RESULTS

A total of 114 relevant papers were included in this review. Numerous anatomical variations are described in the literature. Variations of the optic canal include duplication (0.64%) and keyhole anomaly (2.65%). Variations in pneumatization of the anterior clinoid process were unilateral in almost 10%, bilateral in 9%, and normal in 72%. A rare variant of the superior orbital fissure (SOF) is Warwick's foramen, which appears as if the lowest portion of the SOF was separated from the main fissure by a transverse bony bridge.

CONCLUSION

The definition of the orbital apex varies in the literature, and further research would most likely identify additional variations. A universal definition reporting these variations and pathology and imaging findings is essential for determining the optimal surgical approach to the orbital apex.

Meningo-orbital band detachment: A key step for the extradural exposure of the cavernous sinus and anterior clinoid process

The meningo-orbital band (MOB) is the most superficial dural band that tethers the fronto-temporal dura to the periorbita. It is usually encountered when performing a pterional or fronto-temporo-sphenoidal approach, and it disrupts surgical access to deeper regions. Our objective was to perform a detailed anatomy study and a stepwise method to successfully detach the MOB using cadaveric specimens. We used six formalin-fixed, silicone-injected cadaveric heads. On each side, we performed a pterional approach plus mini-peeling of the anterior third of the middle fossa and/or extradural anterior clinoidectomy. We also applied this technique in three clinical cases to prove its safety and efficacy. The detachment of the MOB consists in four steps, 1) detachment of the temporal and frontal dura, 2) cutting of the MOB, 3) exposure and drilling of the anterior clinoid process, and 4) pealing of the lateral wall of the cavernous sinus. Using clinical cases, we explain how to adapt the technique depending on the localization of the lesion. The detachment of the MOB is the key to safely expose the cavernous sinus and the anterior clinoid process. The authors proposed a step-by-step method for the safe and effective detachment of the MOB. It is recommended, particularly to less experienced neurosurgeons that are starting with skull base surgery, and also to experts that want to expand their knowledge.

Orbitomeningeal Band in Transcavernous Dissection and Anterior Clinoidectomy: 3-Dimensional Operative Video

The orbitomeningeal or meningo-orbital band (MOB) has been described as the most superficial dural band responsible for tethering the frontotemporal basal dura to the periorbita.1,2 The MBO usually interferes with the surgical approach to the most profound areas of the anterior and middle skull base. It is known that there are no cranial nerves on the lateral surface of the superior orbital fissure; therefore, the neurosurgeon can cut the MOB without causing any neurological deficit and, at the same time, achieving fully exposure of the anterior clinoid process1-4 and/or the lateral wall of the cavernous sinus.5 The purpose of this video is to describe the microsurgical anatomy of the MOB and illustrate the technique for its detachment, accompanied by 2 illustrative cases. To achieve this, we use 3-dimensional recordings of 2 cadaveric specimens' dissections performed by the senior author. Case 1: 58-yr-old female with left blindness. Magnetic resonance imaging (MRI) shows an anterior and middle skull base lesion with orbital compression. Case 2: 32-yr-old male presenting with headache and trigeminal neuralgia. The MRI revealed an hourglass-shaped lesion in the posterior and middle fossa. Both patients signed an informed consent and agree with the use of their images for research purposes. We used a step-by-step approach for an adequate and secure dissection of the MOB highlighting the anatomic structures involved in the process. This approach allows safe and adequate access to the deeper structures of the anterior and middle skull base.

Anterior Clinoid Metastasis as First Presentation of a Signet Ring Cell Carcinoma: An Intriguing Diagnosis

Background  We report an extremely unusual case of anterior clinoid process (ACP) metastasis as the first presentation of a signet ring cell carcinoma.

Case Description  A 54-year-old female patient presented with right-sided visual disturbances due to optic nerve compression from a computed tomography (CT)-identified right anterior clinoid bone lesion. Contrast-enhanced magnetic resonance imaging showed an extra-axial, well-bordered enhancing mass extending from the right ACP toward the inner lumen of the optic canal. Pterional approach was adopted to remove the lesion and decompress the optic canal. Histological examination demonstrated a metastasis from a signet ring cell carcinoma. Postoperative CT showed near-total resection of the tumor and decompression of the optic canal. Visual defect remained unchanged.

Conclusion  Metastasis should be considered in the differential diagnosis of the ACP lesions. The early suspicion and identification of this extremely rare pathological entity can be helpful for the prompt management of patients, especially in the absence of any other signs of oncological diseases.

Endoscopic endonasal anterior clinoidectomy: surgical anatomy, technique nuance, and case series

Advances in endoscopic technique allow for resection of the anterior clinoid process (ACP) via an endoscopic endonasal approach. The authors discuss the endoscopic endonasal anterior clinoidectomy (EEAC) and demonstrate the relevant surgical anatomy and technical nuances. The approach was simulated in 6 cadaveric heads. From a technical point of view, the lateral optic carotid recess was used as the landmark in the proposed technique. The superomedial, superolateral, and inferior vertices of this recess are the main operative points. The EEAC approach was achieved by disconnecting the ACP tip from the base by drilling the 3 vertices. The proposed approach was successfully performed in all cadaveric specimens. Then, in a case series involving 6 patients in whom the EEAC approach was used, there were no vascular injuries; 2 patients had postoperative oculomotor nerve palsy, which improved in one and resolved in the other by 1 month.The EEAC approach for tumors and vascular lesions in the parasellar region is technically feasible. The surgical corridor is increased by ACP resection, although to a lesser extent than the transcranial anterior clinoidectomy. Based on the authors' initial anatomical and surgical results, resection of the ACP via the endonasal endoscopic approach is a novel technique worth exploring in suitable cases.

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.

The Orbitozygomatic Craniotomy and Its Judicious Use

The concept of maximizing bone removal along the skull base has been advocated to expand the operative space for large, firm, and encasing ventral and ventrolateral skull base tumors. However, indications for the use of such osteotomies have not been well defined. The improved maneuverability and enhanced extent of expansion of the operative corridor via the skull base approaches compared to those of standard craniotomies have been based on cadaveric studies that might not simulate the operative environment realistically. Bony removal alone is not adequate to protect neurovascular structures, and strategic use of dynamic retraction and innovative operative routes are some of the other factors that contribute to successful microsurgery. In this analysis, the more discriminate indications and modified techniques for orbitozygomatic osteotomy are discussed.

Anatomical meningo-orbital band evaluation and clinical implications: a cadaveric dissection study

BACKGROUND

The meningo-orbital band (MOB) is a dural structure which runs around the superior orbital fissure (SOF) tethering the frontotemporal basal dura to the periorbita, through the SOF. MOB division is important to expose and remove the anterior clinoid process, to access to proximal carotid artery and cavernous sinus area. The goal of the study was to measure how the MOB could be safely incised without cranial nerves and cavernous sinus injuries.

METHODS

Anatomical dissections and extradural exposure of the anterior clinoid process was performed on 20 cadavers (40 sides). Measurement of the MOB thickness was performed before its incision, after dura propria dissection, and retraction off the inner cavernous membrane, to expose the cranial nerves.

RESULTS

We analyzed 20 cadaveric formalin-fixed heads injected with colored silicone, 11 man and 9 woman of caucasian race. The average length of a safe incision of the MOB was 10.6 ± 1.1 mm on the right side, and 10.65 ± 1.09 mm on the left side.

CONCLUSIONS

In our study the average length of a safe incision of the MOB was 10.6 ± 1.1 mm. Thus, the incision length of the MOB should not exceed 9 mm; the peeling of the anterior cavernous sinus and of the SOF, dissecting the two layers of the dura throughout the incision of the MOB, is an useful technique to avoid cranial nerves and cavernous sinus lesions.

Anterior clinoidectomy using an extradural and intradural 2-step hybrid technique

In Brief: The authors found a practical intraoperative landmark to localize the optic strut during anterior clinoidectomy and used it as the basis for performing anterior clinoidectomy in two steps: extradural phase and intradural phase. This anatomically based technique can increase the safety of anterior clinoidectomy by providing easily identifiable landmarks and reducing intradural bone drilling, which could put the adjacent neurovauscular structures at risk.

Less Invasive Modified Extradural Temporopolar Approach for Paraclinoid Lesions: Operative Technique and Surgical Results in 80 Consecutive Patients

Background  Extradural temporopolar approach for paraclinoid lesions can provide extensive and early exposure of the anterior clinoid process, and complete mobilization and decompression of the optic nerve and internal carotid artery, which can prevent intraoperative neurovascular injury. The present study investigated the usefulness of our less invasive modified technique and discussed its operative nuances. Methods  We retrospectively reviewed medical charts of 80 consecutive patients with neoplastic (21 patients) and vascular lesions (59 patients) who underwent the modified extradural temporopolar approach between September 2009 and March 2014. Results  Preoperative visual acuity worsened in 4 patients (5.0%) and worsening of visual field function occurred in 10 patients (12.5%). Postoperative outcome was good recovery in 71 patients, moderate disability in 6, severe disability in 2, and death in 1 (due to reruptured aneurysm). No operation-related mortality occurred in the series. Conclusion  Less invasive modified extradural temporopolar approach is safe and can be recommended for the surgical treatment of deeply located aneurysms and skull base tumors to reduce the risk of intraoperative optic neurovascular injury.

The Orbitomeningeal Band as a Way to Bloodless Transcavernous Dissection and Anterior Clinoidectomy

The meningo-orbital band (MOB) is a dural fold which runs along the lateral border of the superior orbital fissure and contains few small dural veins and the orbitomeningeal artery. MOB detachment is relatively easy to understand step-wise procedure, provides a wider exposure, and better orientation thus facilitating relatively easy approach to paraclinoid and cavernous sinus region. The present microsurgical technique helps to preserve the true cavernous membrane and thereby providing almost bloodless dissection of the cavernous sinus. The same technique can be used to uncover the anterior clinoid process laterally, posteriorly, superiorly, and also in the inferolateral region thereby decreasing the risk and time of clinoidectomy.

Anterior Clinoid Metastasis Removed Extradurally: First Case Report

Background  We report a case of isolated metastasis on the anterior clinoid process (ACP) mimicking meningioma.

Clinical Presentation  A 58-year-old male presented with headaches, right-sided visual disturbances, and blurred and double vision. The cause of double vision was partial weakness of the right III nerve, resulting from compression of the nerve by “hypertrophied” tumor-involved right anterior clinoid. Medical history revealed two primary malignant tumors—male breast cancer and prostate cancer (diagnosed 6 and 18 months prior, respectively). The patient was treated with chemotherapy and showed no signs of active disease, recurrence, or metastasis. Postcontrast head magnetic resonance imaging (MRI) showed extra-axial well-bordered enhancing mass measuring 1.6 × 1.1 × 1 × 1 cm (anteroposterior, transverse, and craniocaudal dimensions) on the ACP, resembling a clinoidal meningioma. Extradural clinoidectomy with tumor resection was performed via right orbitozygomatic pretemporal skull base approach. Visual symptoms improved. Follow-up MRI showed no signs of tumor residual or recurrence.

Conclusion  This is the first case report of a metastasis of any kind on ACP. Metastasis should be included as a part of the differential diagnosis of lesions of the anterior clinoid. Extradural clinoidectomy is a safe and effective method in the treatment of these tumors.

Extradural anterior clinoidectomy in the management of parasellar meningiomas: Analysis of 13 years of experience and literature review

BACKGROUND AND AIM

The extradural anterior clinoidectomy (EAC) is a key microsurgical technique that facilitates the resection of tumors located in the parasellar region. There is currently no consensus regarding the execution of the procedure via extradural or intradural nor scientific evidence that supports its routine use. The purpose of this article is to expose our experience in performing EAC as part of the management of the parasellar meningiomas.

MATERIALS AND METHODS

A retrospective analysis of the EAC for parasellar meningioma resection performed in our center between 2003 and 2015 was done. A total of 53 patients were recorded. We analized our series focusing on visual outcomes, resection rates and complications. Through an extensive bibliographic research, we discussed the advantages and disadvantages of the EAC, technical considerations, comparison with the intradural clinoidectomy and its visual impact.

RESULTS

The most frequent tumors were anterior clinoidal meningiomas (33.9%). The most common initial symptoms were decreased visual acuity (45.3%) and headache (22.6%). A gross total resection was achieved in 67.9%, being subtotal in the remaining 32.1%. Regarding the visual deficits 67.9% of the patients presented clinical stability, 22.6% improvement and 9.4% worsening. The degree of tumor resection did not significantly influence post-surgical visual outcomes, either visual acuity (P=.71) or campimetric alterations (P=.53). 24.5% of the patients experienced iiinerve transient paresis and 1.9% permanent. The postoperative cerebrospinal fluid leak rate was 3.8%. Mortality rate was 0%. The mean follow-up was 82.3 months.

CONCLUSIONS

In our experience, EAC is a safe technique that facilitates the resection of the meningiomas located in the parasellar area, helps to achieve early tumor devascularization, reduces the need for retraction of the cerebral parenchyma and could play a positive role in the preservation of visual function and the appearance of tumor recurrences in the anterior clinoid process (ACP).

Modified Extradural Temporopolar Approach for Paraclinoid Aneurysms: Operative Nuance and Surgical Result

BACKGROUND

Extradural temporopolar approach can provide extensive exposure of the anterior clinoid process, which can prevent intraoperative neurovascular injury in anterior clinoidectomy for paraclinoid aneurysms. The present study investigates the usefulness of this modified technique, and operative nuances are discussed here.

METHODS

We retrospectively reviewed the medical charts of 30 consecutive patients with paraclinoid aneurysms who underwent treatment with this modified extradural temporopolar approach between September 2009 and March 2016.

RESULTS

Worsening of visual acuity was documented postoperatively in three patients (10.0%), and visual field function worsened in three patients (10.0%). Postoperative outcome was good recovery in all patients. No operation-related mortality occurred in the series.

CONCLUSION

Extradural anterior clinoidectomy via the modified extradural temporopolar approach is safe and may be recommended for surgical treatment of paraclinoid aneurysms to reduce the risk of intraoperative optic neurovascular injury.

Modified extradural temporopolar approach with mini-peeling of dura propria for paraclinoid and/or parasellar tumors: Operative technique and nuances

Background:

Modified extradural temporopolar approach (EDTPA) with mini-peeling of the dura propria can provide extensive exposure of the anterior clinoid process and early exposure, as well as complete mobilization and decompression of the optic nerve and internal carotid artery, which can prevent intraoperative neurovascular injury for paraclinoid and/or parasellar lesions. The present study investigated the usefulness of this modified technique and discusses the operative nuances.

Methods:

We retrospectively reviewed medical charts of 27 consecutive patients with neoplastic paraclinoid and/or parasellar lesions who underwent this modified approach between September 2009 and August 2016.

Results:

Preoperative visual acuity worsened in 2 patients (7.4%), and worsening of visual field function occurred in 2 patients (7.4%). Postoperative outcome was good recovery in 25 patients (92.6%) and moderate disability in 2 (7.4%). No operation-related mortality occurred in the series.

Conclusions:

The modified EDTPA is safe and recommended for surgical treatment of paraclinoid and/or parasellar tumors to reduce the risk of intraoperative optic neurovascular injury.

Modified extradural temporopolar approach with suction decompression for clipping of large paraclinoid aneurysm: Technical note

Background:

Surgical clipping of complicated large paraclinoid aneurysms are still challenging because strong adhesion of aneurysm itself may hinder the dissection of the perforators and the surrounding anatomical structures from the aneurysm dome.

Methods:

We describe 13 consecutive patients and the clipping of complicated, large-sized paraclinoid aneurysms using a modified extradural temporopolar approach combined with retrograde suction decompression and discuss its advantages and pitfalls.

Results:

Modified extradural temporopolar approach with suction decompression (SD) assistance was performed in all patients. There was no complication related to the surgical procedure. Postoperative outcome was good recovery in 7 patients, moderate disability in 4, and severe disability in 2 caused by severe subarachnoid hemorrhage. Favorable outcomes were achieved in 10 patients (84.6%).

Conclusion:

We recommend its less invasive, safe, and useful combined technique in the treatment of symptomatic paraclinoid aneurysms, which carry the risk of neurovascular injury caused by dissection from the aneurysm dome.

Quantitative Anterior and Posterior Clinoidectomy Analysis and Mobilization of the Oculomotor Nerve during Surgical Exposure of the Basilar Apex Using Frameless Stereotaxis

Background  Anterior and posterior clinoidectomies have been proposed to augment exposure of the basilar apex. A sequential quantitative benefit analysis offered by these maneuvers has not been reported. Methods  Fourteen datasets from eight cadaveric specimens were analyzed. A modified orbitozygomatic frontotemporal craniotomy was performed. The extent of proximal control of the basilar artery was determined through the exposed opticocarotid and carotidoculomotor triangles before and after clinoidectomies and mobilization of the third nerve at the porous oculomotarius. Results  Removal of the anterior and posterior clinoids significantly improved proximal basilar artery access ( p  < 0.012) and increased the opticocarotid triangle and carotidoculomotor triangle areas ( p  < 0.017). Surgical freedom increased inferosuperiorally in the opticocarotid triangle following anterior clinoidectomy ( p  < 0.047) and in carotidoculomotor triangle following posterior clinoidectomy ( p  < 0.047). Mobilization of the third nerve increased surgical freedom in the mediolateral projection of the carotidoculomotor triangle ( p  < 0.047). Conclusion  Anterior and posterior clinoidectomies significantly improved the area of exposure of the opticocarotid triangle, carotidoculomotor triangle, and the exposed length of the basilar artery available for proximal control. This improvement is extremely important for large or giant aneurysms of the upper basilar artery or aneurysms hidden by the posterior clinoid.

Impact of optic canal decompression on visual outcome in subtotal resected skull base meningiomas

BACKGROUND

Visual impairment (VI) due to neoplastic infiltration of the optic canal (OC) is frequently seen in skull base meningiomas representing a significant restriction in patients` quality of life. However, the delicate anatomy of this region often prevents gross total tumor resection. The aim of the present study was to evaluate the impact of intradural OC decompression and postoperative oncological procedure on preservation of visual acuity in subtotal resected skull base meningiomas.

METHODS

A retrospective analysis of 31 consecutive patients (19 females, 12 males; mean age 53 [range 18-78]), treated in our institution between 01/2011- 09/2014 was performed. Patients` charts were analyzed with special respect to operative procedure, postoperative treatment and procedural impact on late visual function.

RESULTS

Most patients (74.2%) had VI prior to surgery. A pterional craniotomy (97%) facilitated subtotal tumor removal in 71% of the patients with no intraoperative and a low rate (6.4%) of postoperative complications. Adjunctive radiotherapy was performed in 19.3% of the patients. Preoperative visual acuity was preserved or improved in 92% of the patients. Substantial tumor regrowth occurred in only 11.2% of the patients.

CONCLUSIONS

Intradural decompression of the OC stabilizes visual function in subtotally resected skull base meningiomas. Moreover, adjuvant radiotherapy seems to further benefit visual outcome which has to be evaluated in further prospective studies.

Endoscopic endonasal management of cerebrospinal fluid rhinorrhea after anterior clinoidectomy for aneurysm surgery: changing the paradigm of complication management

Resection of the anterior clinoid process results in the creation of the clinoid space, an important surgical step in the exposure and clipping of clinoidal and supraclinoidal internal carotid artery aneurysms. Cerebrospinal fluid rhinorrhea is an undesired and potentially serious complication. Conservative measures may be unsuccesful, and there is no consensus on the most appropriate surgical treatment. Two patients with persistent transclinoidal CSF rhinorrhea after aneurysm surgery were successfully treated with a combined endoscopic transnasal/transeptal binostril approach using a fat graft and ipsilateral mucosal nasal septal flap. Anatomical considerations and details of the surgical technique employed are discussed, and a management plan is proposed.

The Extended Lateral Supraorbital Approach and Extradural Anterior Clinoidectomy Through a Frontopterio-Orbital Window: Technical Note and Pilot Surgical Series

BACKGROUND

Lateral approaches to treat anterior cranial fossa lesions have evolved since the first frontotemporal approach described by Dandy in 1918. We describe a less invasive approach to perform extradural anterior clinoidectomy through a lateral supraorbital (LSO) approach for anterior circulation aneurysms and anterolateral skull base lesions.

METHODS

The extended LSO approach involves performing a standard lateral supraorbital craniotomy followed by drilling of the sphenoid wing and lateral wall of the orbit through the frontal bony opening of the LSO approach, without any temporal extension of the craniotomy. This creates a frontopterio-orbital window exposing the periorbita; superior, medial, and anterior aspect of the temporal dura mater; and superior orbital fissure. After unroofing the superior orbital fissure, the meningo-orbital fold is cut, and the temporal dura mater is peeled from the lateral wall of the cavernous sinus to expose the anterior clinoid process allowing a standard opening of the optic canal and anterior clinoidectomy.

RESULTS

The extended LSO approach and extradural anterior clinoidectomy allowed access to 4 sphenoid wing/anterior clinoidal meningiomas, 5 anterior circulation aneurysms, 2 temporomesial lesions, and 1 orbital/cavernous sinus abscess. Postoperatively, 2 patients had transient hemiparesis, 2 patients had transient third nerve palsy, and 1 patient had minimal visual field deterioration. All patients had a modified Rankin Scale score ≤1 at 8-week follow-up.

CONCLUSION

The extended LSO approach opens a new route (frontopterio-orbital window) to perform extradural anterior clinoidectomy safely and increases surgical exposure, angles, and operability of a less invasive keyhole craniotomy (LSO approach) to treat anterior cranial fossa lesions.

Surgically Clipping a Posterolaterally Projecting Posterior Communicating Artery Aneurysm With Anterior Petroclinoid Fold Fenestration

The anterior petroclinoid fold (APF) is a ligamentous structure consisting of collagen fiber and extends from the petrous apex to the anterior clinoid process. During the surgical clipping of some posterolaterally projecting posterior communicating artery aneurysms, it may pose a technical challenge due to obscuration of the aneurismal neck by the APF. Herein, the authors describe a simple and effective technique utilizing fenestration of the APF to facilitate visualization and surgical clipping of these aneurysms. To the best knowledge of us, this technique of the APF fenestration has been reported in only a few patients.

Operative surgical nuances of modified extradural temporopolar approach with mini-peeling of dura propria based on cadaveric anatomical study of lateral cavernous structures

Background:

Extradural temporopolar approach (ETA) has been modified as less invasive manner and named as trans-superior orbital fissure (SOF) approach with mini-peeling technique. The present study discusses the operative nuances of this modified technique on the basis of cadaveric study of lateral cavernous structures.

Methods:

In five consecutive cadaveric specimens, we performed an extradural anterior clinoidectomy with mini-peeling of the dura propria to expose the anterior clinoid process entirely. We also investigated the histological characteristics of the lateral cavernous sinus (CS) between the dura propria and periosteal dura at the SOF, foramen rotundum (FR), and foramen ovale (FO) levels, and of each trigeminal nerve division.

Results:

Coronal histological examination of the lateral wall of the CS showed invagination of the dura propria and periosteal dura into the SOF. In contrast, no such invagination was observed at the levels of the FR and FO. This finding supports the technical rationale of the only skeletonization of the SOF for peeling of the dura propria but not FR. In addition, our modified ETA method needs only minimal dural incision between the SOF and FR where no cranial nerves are present.

Conclusion:

Our technical modification of ETA may be recommended for surgical treatment of paraclinoid lesions to reduce the risk of intraoperative neurovascular injury.

Usefulness of Extradural Optic Nerve Decompression via Trans-Superior Orbital Fissure Approach for Treatment of Traumatic Optic Nerve Injury: Surgical Procedures and Techniques from Experience with 8 Consecutive Patients

OBJECTIVE

To describe our experience of extradural optic nerve decompression via the trans-superior orbital fissure approach for traumatic optic neuropathy (TON) and retrospectively analyze its advantages and pitfalls.

METHODS

Between September 2009 and August 2014, 8 consecutive patients with TON underwent extradural optic canal decompression via the trans-superior orbital fissure approach. We retrospectively reviewed medical charts, radiologic findings, surgical techniques, complications, and final surgical results.

RESULTS

All 8 patients presented with visual disturbance caused by head injury; 2 patients had no light perception, 6 had light perception, and 2 had ophthalmoplegia. All patients underwent extradural optic canal decompression and high-dose steroid administration within 24 hours after injury. Postoperative visual acuity on discharge was improved in 6 patients and unchanged in 2. The 2 patients with ophthalmoplegia gradually recovered by 3 months after operation. The postoperative outcome was good recovery in 7 patients and moderate disability in 1 patient. There were no complications related to the surgical procedure.

CONCLUSIONS

Emergent optic canal release has been recommended in patients with TON. The advantage of the extradural optic canal decompression via the trans-superior orbital fissure approach is easy identification of the optic canal after partial removal of the anterior clinoid process, resulting in fewer surgical complications. In addition, this procedure can achieve intraorbital decompression if necessary. We recommend this modified approach with mini-peeling as a safe and reliable procedure in patients with TON.

Anterior clinoid process and the surrounding structures

BACKGROUND

The anterior clinoid process (ACP) is located close to the optic nerve, internal carotid artery, ophthalmic artery, and can be easily injured in an ACP-related surgery. An anatomical study clearly defining the ACP is of great importance. In addition, computed tomographic (CT) images may be a new tool for the anatomical analysis of ACP compared with the use of a cadaver and skull study, and more data related to ACP can be measured by CT images.

PURPOSE

We studied the anatomical structure of ACP and the structures surrounding it to provide information to surgeons for ACP-related surgery.

METHODS

Computed tomography angiographic images of 102 individuals were reviewed. The measurement was performed on coronal, sagittal, and axis planes after multiplanar reformation. The length of ACP and the distance between apex of ACP and sagittal midline were measured in the axial plane; the classification of ACP and the occurrence rate of bone bridge were also viewed in axial plane. The thickness of ACP was measured in sagittal plane.

RESULT

In Chinese population, 12.3% of the ACP is gasified, and the pneumatization of ACP has a relationship with the pneumatization of sphenoid sinus. The length and thickness of ACP are similar to that in previous studies in cadaver. The apex of ACP is relatively stationary to the C3 and C4 segments of the internal carotid artery. The occurrence rate of anterior and middle clinoid bone bridge was 7.8%; the occurrence rate of anterior and posterior clinoid bone bridge was 9.3%.

CONCLUSIONS

The anatomical structure of ACP can be studied effectively in CT images. Recognizing the anatomical characteristics of the ACP and optic strut is important in decreasing the incidence of surgical complications of an anterior clinoidectomy and in the proper intraoperative management to prevent these complications.

Quantitative analysis of variable extent of anterior clinoidectomy with intradural and extradural approaches: 3-dimensional analysis and cadaver dissection

BACKGROUND

Drilling of the anterior clinoid process (ACP) is an integral component of surgical approaches for central and paracentral skull base lesions. The technique to drill ACP has evolved from pure intradural to extradural and combined techniques.

OBJECTIVE

To describe the computerized morphometric evaluation of exposure of optic nerve and internal carotid artery with proposed tailored intradural (IDAC) and complete extradural (EDAC) anterior clinoidectomy.

METHODS

We describe a morphometric subdivision of ACP into 4 quadrangles and 1 triangle on the basis of fixed bony landmarks. Computerized volumetric analysis with 3-dimensional laser scanning of dry-drilled bones for respective tailored IDAC and EDAC was performed. Both approaches were compared for the area and length of the optic nerve and internal carotid artery. Five cadaver heads were dissected on alternate sides with intradural and extradural techniques to evaluate exposure, surgical freedom, and angulation of approach.

RESULTS

Complete anterior clinoidectomy provides a 2.5-times larger area and 2.7-times larger volume of ACP. Complete clinoidectomy deroofed the optic nerve to an equal extent as by proposed the partial tailored clinoidectomy approach. Tailored IDAC exposes only the distal dural ring, whereas complete EDAC exposes both the proximal and distal dural rings with complete exposure of the carotid cave.

CONCLUSION

Quantitative comparative evaluation provides details of exposure and surgical ease with both techniques. We promote hybrid/EDAC technique for vascular pathologies because of better anatomic orientation. Extradural clinoidectomy is the preferred technique for midline cranial neoplasia. An awareness of different variations of clinoidectomy can prevent dependency on any particular approach and facilitate flexibility.

Japanese neurosurgeons and microsurgical anatomy: a historical review

Research in microneurosurgical anatomy has contributed to great advances in neurosurgery in the last 40 years. Many Japanese neurosurgeons have traveled abroad to study microsurgical anatomy and played major roles in advancing and spreading the knowledge of anatomy, overcoming their disadvantage that the cadaver study has been strictly limited inside Japan. In Japan, they initiated an educational system for surgical anatomy that has contributed to the development and standardization of Japanese neurosurgery. For example, the Japanese Society for Microsurgical Anatomy started an annual educational meeting in the middle of 1980s and published its proceedings in Japanese every year for approximately 20 years. These are some of the achievements that bring worldwide credit to Japanese neurosurgeons. Not only should Japanese neurosurgeons improve their educational system but they should also contribute to the international education in this field, particularly in Asia.

Internal carotid artery reconstruction using multiple fenestrated clips for complete occlusion of large paraclinoid aneurysms

Objective

Although surgical techniques for clipping paraclinoid aneurysms have evolved significantly in recent times, direct microsurgical clipping of large and giant paraclinoid aneurysms remains a formidable surgical challenge. We review here our surgical experiences in direct surgical clipping of large and giant paraclinoid aneurysms, especially in dealing with anterior clinoidectomy, distal dural ring resection, optic canal unroofing, clipping techniques, and surgical complications.

Methods

Between September 2001 and February 2012, we directly obliterated ten large and giant paraclinoid aneurysms. In all cases, tailored orbito-zygomatic craniotomies with extradural and/or intradural clinoidectomy were performed. The efficacy of surgical clipping was evaluated with postoperative digital subtraction angiography and computed tomographic angiography.

Results

Of the ten cases reported, five each were of ruptured and unruptured aneurysms. Five aneurysms occurred in the carotid cave, two in the superior hypophyseal artery, two in the intracavernous, and one in the posterior wall. The mean diameter of the aneurysms sac was 18.8 mm in the greatest dimension. All large and giant paraclinoid aneurysms were obliterated with direct neck clipping without bypass. With the exception of the one intracavenous aneurysm, all large and giant paraclinoid aneurysms were occluded completely.

Conclusion

The key features of successful surgical clipping of large and giant paraclinoid aneurysms include enhancing exposure of proximal neck of aneurysms, establishing proximal control, and completely obliterating aneurysms with minimal manipulation of the optic nerve. Our results suggest that internal carotid artery reconstruction using multiple fenestrated clips without bypass may potentially achieve complete occlusion of large paraclinoid aneurysms.

The Meningo-Orbital Band: Microsurgical Anatomy and Surgical Detachment of the Membranous Structures through a Frontotemporal Craniotomy with Removal of the Anterior Clinoid Process

Objective To describe the microanatomy of the meningo-orbital band (MOB) and its associated membranes, and propose a stepwise method for their detachment while minimizing potential complications. Design Cadaveric and prospective clinical. Setting Microneurosurgery Skull Base Laboratory, Weill Cornell Medical College (New York, NY) and Shiroyama Hospital (Osaka, Japan). Participants Five preserved cadaveric heads (10 sides) and five patients requiring surgical detachment of the MOB in 2012. Results MOB detachment and subsequent extradural anterior clinoidectomies were successfully performed on five clinical cases. Detachment of the MOB was accomplished using a four-step dissection based on the structure's detailed microanatomy and included (1) partial removal of the lateral wall of the superior orbital fissure, (2) incising of the lateral periosteal dura of the superior orbital fissure, (3) peeling off the dura propria of the temporal lobe from the inner cavernous membrane, and (4) fully detaching the exposed MOB from the periorbita. Conclusion Understanding the complex microanatomy of these structures enabled a safe and effective stepwise detachment of the MOB. We recommend that surgeons possess sufficient anatomical knowledge before surgically manipulating this structure.

Measurement of Critical Structures around Paraclinoidal Area : A Cadaveric Morphometric Study

OBJECTIVE

Although removal of the anterior clinoid process (ACP) is essential surgical technique, studies about quantitative measurements of the space broadening by the anterior clinoidectomy are rare. The purposes of this study are to investigate the dimension of the ACP, to quantify the improved exposure of the parasellar space after extradural anterior clinoidectomy and to measure the correlation of each structure around the paraclinoidal area.

METHODS

Eleven formalin-fixed Korean adult cadaveric heads were used and frontotemporal craniotomies were done bilaterally. The length of C6 segment of the internal carotid artery on its lateral and medial side and optic nerve length were checked before and after anterior clinoidectomy. The basal width and height of the ACP were measured. The relationships among the paraclinoidal structures were assessed. The origin and projection of the ophthalmic artery (OA) were investigated.

RESULTS

The mean values of intradural basal width and height of the ACP were 10.82 mm and 7.61 mm respectively. The mean length of the C6 lateral and medial side increased 49%. The mean length of optic nerve increased 97%. At the parasellar area, the lengths from the optic strut to the falciform liament, distal dural ring, origin of OA were 6.69 mm, 9.36 mm and 5.99 mm, respectively. The distance between CN III and IV was 11.06 mm.

CONCLUSION

With the removal of ACP, exposure of the C6 segments and optic nerve can expand 49% and 97%, respectively. This technique should be among a surgeon's essential skills for treating lesions around the parasellar area.

How I do it : anterior clinoidectomy and optic canal unroofing for microneurosurgical management of ophthalmic segment aneurysms

BACKGROUND

Power drilling commonly used for anterior clinoidectomy and optic canal unroofing can result in thermal injury to the optic nerve.

METHODS

The authors describe an intradural "limited drill" technique of anterior clinoidectomy and optic canal unroofing for microneurosurgical management of ophthalmic segment aneurysms, where optic canal unroofing is done with 1 mm Kerrison punch and the use of the power drill is restricted to anterior clinoidectomy to avoid thermal injury to the optic nerve. The optic nerve, internal carotid artery (ICA), and aneurysm are covered with wet gelfoam pieces to prevent any inadvertent contact with the drill.

CONCLUSION

"Limited drill technique" is a safe and effective technique of anterior clinoidectomy and optic canal unroofing.

KEY POINTS

• Anterior clinoidectomy and optic canal unroofing is an important skull base technique required for safe clipping of the majority of ophthalmic segment aneurysms • Power drilling commonly used for optic canal unroofing can cause thermal injury to optic nerve • More than 2 mm free space is available around the optic nerve in the optic canal • Foot plate of 1 mm Kerrison punch can be safely introduced within a normal optic canal without causing mechanical injury to the optic nerve • Reflection of posteriorly based dural flap acts as a dural barrier, preventing direct contact of drill bit to optic nerve, internal carotid artery and aneurysm during drilling • Entanglement of cottonoids to rotating drill bit is a major problem in intradural anterior clinoidectomy • Wet gelfoam pieces do not get entangled to the rotating drill bit • Structures surrounding the area of drilling can be covered with wet gel foam pieces to prevent direct contact of the drill to neurovascular structures • Opened cisterns can be covered with wet gelfoam pieces during drilling to prevent deposition of bone dust in the subarachnoid space • "Limited drill technique" of anterior clinoidectomy and optic canal unroofing is a safe and effective technique for the exposure of ophthalmic segment aneurysms.

Safety of drilling for clinoidectomy and optic canal unroofing in anterior skull base surgery

BACKGROUND

Skull base drilling is a necessary and important element of skull base surgery; however, drilling around vulnerable neurovascular structures has certain risks. We aimed to assess the frequency of complications related to drilling the anterior skull base in the area of the optic nerve (ON) and internal carotid artery (ICA), in a large series of patients.

METHODS

We included anterior skull base surgeries performed from 2000 to 2012 that demanded unroofing of the optic canal, with extra- or intradural clinoidectomy and/or drilling of the clinoidal process and lateral aspect of the tuberculum sella. Data was retrieved from a prospective database and supplementary retrospective file review. Our IRB waived the requirement for informed consent. The nature and location of pathology, clinical presentation, surgical techniques, surgical morbidity and mortality, pre- and postoperative vision, and neurological outcomes were reviewed.

RESULTS

There were 205 surgeries, including 22 procedures with bilateral optic canal unroofing (227 optic canals unroofed). There was no mortality, drilling-related vascular damage, or brain trauma. Complications possibly related to drilling included CSF leak (6 patients, 2.9 %), new ipsilateral blindness (3 patients, 1.5 %), visual deterioration (3 patients, 1.5 %), and transient oculomotor palsy (5 patients, 2.4 %). In all patients with new neuropathies, the optic and oculomotor nerves were manipulated during tumor removal; thus, new deficits could have resulted from drilling, or tumor dissection, or both.

CONCLUSION

Drilling of the clinoid process and tuberculum sella, and optic canal unroofing are important surgical techniques, which may be performed relatively safely by a skilled neurosurgeon.