A quantitative comparative surgical analysis of the endoscopic transorbital approach and frontotemporal-orbitozygomatic approach for extradural exposure of the cavernous sinus.

OBJECTIVE: Recently, the endoscopic superior eyelid transorbital approach (SETA) has emerged as a potential alternative to access the cavernous sinus (CS). Several previous studies have attempted to quantitatively compare the traditional open anterolateral skull base approaches with transorbital exposure; however, these comparisons have been limited to the area of exposure provided by the bone opening and trajectory, and fail to account for the main avenues of exposure provided by subsequent requisite surgical maneuvers. The authors quantitatively compare the surgical access provided by the frontotemporal-orbitozygomatic (FTOZ) approach and the SETA following applicable periclinoid surgical maneuvers, evaluate the surgical exposure of key structures in each, and discuss optimal approach selection. METHODS: SETA and FTOZ approaches were performed with subsequent applicable surgical maneuvers on 8 cadaveric heads. The lengths of exposure of cranial nerves (CNs) II-VI and the cavernous internal carotid artery; the areas of the space accessed within the supratrochlear, infratrochlear, and supramaxillary (anteromedial) triangles; the total area of exposure; and the angles of attack were measured and compared. RESULTS: Exposure of the extradural CS was comparable between approaches, whereas access was significantly greater in the FTOZ approach compared with the SETA. The lengths of extradural exposure of CN III, V1, V2, and V3 were comparable between approaches. The FTOZ approach provided marginally increased exposure of CNs IV (20.9 ± 2.36 mm vs 13.4 ± 3.97 mm, p = 0.023) and VI (14.1 ± 2.44 mm vs 9.22 ± 3.45 mm, p = 0.066). The FTOZ also provided significantly larger vertical (44.5° ± 6.15° vs 18.4° ± 1.65°, p = 0.002) and horizontal (41.5° ± 5.40° vs 15.3° ± 5.06°, p < 0.001) angles of attack, and thus significantly greater surgical freedom, and provided significantly greater access to the supratrochlear (p = 0.021) and infratrochlear (p = 0.007) triangles, and significantly greater exposure of the cavernous internal carotid artery (17.2 ± 1.70 mm vs 8.05 ± 2.37 mm, p = 0.001). Total area of exposure was also significantly larger in the FTOZ, which provided wide access to the lateral wall of the CS as well as the possibility for intradural access. CONCLUSIONS: This is the first study to quantitatively identify the relative advantages of the FTOZ and transorbital approaches at the target region following requisite surgical maneuvers. Understanding these data will aid in selecting an optimal approach and maneuver set based on target lesion size and location.

The complete anterior petrosectomy: an expanded extended-middle fossa approach with removal of the infratrigeminal petrous apex and drilling of the lateral clivus.

Intradural exposure in the extended middle fossa anterior transpetrosal approach is traditionally limited to the inferior petrosal sinus inferomedially. Expanding bone removal of the petrous apex around the petrous internal carotid artery (ICA), underneath the trigeminal ganglion/mandibular nerve, and into the lateral component of the clivus can significantly expand the limits of this approach beyond the inferior petrosal sinus and allows for exposure of the midline structures, aspects of the contralateral inferior clival region, and, when high riding, the vertebrobasilar junction. To date, no descriptive techniques for drilling into the lateral clivus in this approach have been published. The authors provide a detailed stepwise description of their complete anterior petrosectomy, in use at their institution, that involves skeletonization of the posteromedial petrous ICA, gentle elevation of the trigeminal ganglion/mandibular nerve, removal of the infratrigeminal petrous apex, and two techniques for drilling into the lateral clivus along the petroclival fissure. These techniques provide a direct and unobstructed corridor to the midpetroclival region and ventral brainstem with greater maneuverability and enhanced control of the midline structures, which is especially useful for resection of petroclival meningiomas, chondrosarcomas, and giant vascular lesions of the mid- and upper basilar artery and its proximal branches.

Quantitative analysis of external carotid artery bypass donor vessels by recipient and approach.

INTRODUCTION: Utilization an in-situ pedicle of the external carotid artery (ECA) as an arterial donor can allow for the successful augmentation or replacement of flow to a large vascular territory. We propose a mathematical model for quantitatively analyzing and grading the suitability of donor and recipient bypass vessels based on a set of anatomical and surgical variables in order to predict which pair has the greatest possibility for success. Using this method, we analyze all of the potential donor-recipient pairs for each ECA donor vessel-including the superficial temporal (STA), middle meningeal (MMA), and occipital (OA) arteries. METHODS: The ECA pedicles were dissected in frontotemporal, middle fossa, subtemporal, retrosigmoid, far lateral, suboccipital, supracerebellar, and occipital transtentorial approaches. For each approach, every potential donor-recipient pair was identified, and donor length and diameter were measured as well as depth of field, angle of exposure, ease of proximal control, maneuverability, and length and diameter of the recipient segment. Anastomotic pair scores were determined by adding the weighted donor and recipient. RESULTS: The best overall anastomotic pairs were OA-vertebral artery (V3, 17.1) and STA-insular (M2, 16.3) and STA-sylvian (M3, 15.9) segments of the middle cerebral artery. Other strong anastomotic combinations were OA- telovelotonsillar (15) and OA- tonsilomedullary (14.9) segments of the posterior inferior cerebellar artery, and MMA-lateral pontomesencephalic segment of the superior cerebellar artery (14.2). CONCLUSIONS: This novel model for anastamotic pair scoring can serve as a useful clinical tool for selecting the optimal donor, recipient, and approach combination that can help facilitate a successful bypass.

Anterolateral Routes to the Skull Base-The Frontotemporal Approaches and Exposure of the Sellar and Parasellar Regions.

Surgical approaches to the sellar and parasellar regions are highly challenging due to the densely packed nature of the traversing neurovasculature. The frontotemporal-orbitozygomatic approach offers a wide angle of exposure for the management of lesions involving the cavernous sinus, parasellar region, upper clivus, and adjacent neurovascular structures. It combines the pterional approach with different osteotomies that remove the superior and lateral walls of the orbit and zygomatic arch. Extradural exposure and preparation of the periclinoid region, whether as initial preparation for a combined intraextradural approach to deep-seated skull base targets or as the main avenue of surgical exposure, can substantially enlarge surgical corridors and minimize the need for brain retraction in this very confined microsurgical space. We provide a stepwise description of how we perform the fronto-orbitozygomatic approach and an associated series of surgical maneuvers and techniques that can be utilized in a variety of anterior and anterolateral approaches, either alone or in combination, to tailor exposure to a given lesion. These techniques are not limited to traditional skull base approaches and represent a valuable addition to every neurosurgeon's armamentarium as enhancements to common surgical approaches.

Transpetrosal Routes to the Skull Base-Anterior and Posterior Transpetrosal Approaches.

The extended middle fossa approach with anterior petrosectomy, or anterior transpetrosal approach, is a highly effective and direct approach to difficult-to-access petroclival tumors and basilar artery aneurysms. This surgical approach exposes a significant window of the posterior fossa dura between the mandibular nerve, internal auditory canal, and petrous internal carotid artery, below the level of the petrous ridge, and provides an unobstructed view of the middle fossa floor to the upper half of the clivus and petrous apex, without requiring removal of the zygoma. The posterior transpetrosal approaches, including the perilabyrinthine, translabyrinthine, and transcochlear approaches, provide direct and wide exposure of the cerebellopontine angle and posterior petroclival region. The translabyrinthine approach is commonly used for the removal of acoustic neuromas and other lesions of the cerebellopontine angle. We provide a stepwise description of how we perform these approaches and how to combine and extend them in order to achieve transtentorial exposure.

Posterolateral Routes to the Skull Base, Craniocervical Junction, and Jugular Foramen-The Far Lateral Transcondylar Approach and Combined Transpetrosal Transcervical Approaches.

The far lateral approach provides wide surgical access to the lower third of the clivus, pontomedullary junction, and anterolateral foramen magnum and rarely requires craniovertebral fusion. The most common indications for this approach are posterior inferior cerebellar artery and vertebral arteryaneurysms, brainstem cavernous malformations, and tumors anterior to the lower pons and medulla, including meningiomas of the anterior foramen magnum, schwannomas of the lower cranial nerves, and intramedullary tumors at the craniocervical junction. We provide a stepwise description of how we perform the far lateral approach, as well as how to combine the far lateral approach with other skull base approaches, including the subtemporal transtentorial approach, for lesions involving the upper clivus; the posterior transpetrosal approach, for lesions involving the cerebellopontine angle and/or petroclival region; and/or lateral cervical approaches, for lesions involving the jugular foramen or carotid sheath regions.

Tailored Surgical Access to the Cavernous Sinus and Parasellar Region: Assessment of Cavernous Sinus Entry Corridors and the Periclinoid and Pericavernous Surgical Maneuvers.

BACKGROUND: Lesions involving the cavernous sinus (CS) represent some of the most challenging pathologies of the skull base owing to the dense traversing and surrounding neurovasculature. Extradural exposure and preparation of this region, whether as initial preparation for a combined intra-extradural approach or as the main avenue of surgical exposure, can enlarge surgical corridors and minimize the need for brain retraction in this very confined space. We provide a detailed assessment of the entry corridors to the CS that are available within each approach, the surgical exposure and freedom provided by each of these corridors, and demonstrate how extradural and intradural preparation of these corridors can be used to widen the available working space and facilitate surgery. METHODS: Pterional, frontotemporal-orbital, frontotemporal-orbitozygomatic, frontotemporal-zygomatic, perilabyrinthine transtentorial, and endoscopic transnasal transsphenoidal approaches were performed on cadaveric heads to access the perisellar and CS regions. Periclinoid maneuvers (extradural cutting of the meningo-orbital band, anterior clinoidectomy, unroofing of the optic canal, opening of the superior orbital fissure, displacement of the extra-annular structures, opening of the annulus of Zinn, and interdural dissection), pericavernous maneuvers (intradural cutting of the distal dural ring, mobilization of the supraclinoid internal carotid artery, opening of the oculomotor porus, and mobilization of cranial nerve (CN) III), peritrigeminal extensions (extradural mobilization of CN V2 [maxillary] and/or V3 [mandibular]), and other surgical maneuvers were performed and evaluated. The CS was divided into 8 anatomical compartments and 9 entry corridors were described, and exposure and freedom were assessed accordingly. RESULTS: Intradurally, the standard unextended pterional, frontotemporal-orbital, and frontotemporal orbitozygomatic transsylvian approaches provided access solely to the parasellar entry corridor into the superior wall of the CS. Expanding these approaches with extradural periclinoid maneuvers allowed for subsequent application of the intradural pericavernous maneuvers and enlargement of the parasellar corridor and exposure of the carotid cave. Extradurally, the frontotemporal-orbital approach could be expanded via application of periclinoid maneuvers, which provided access to the anterior portions of the main lateral wall entry corridors. The frontotemporal-orbitozygomatic approach could also be expanded with periclinoid maneuvers to provide extradural access to all 6 lateral wall entry corridors. The extradural frontotemporal-zygomatic approach only provided exposure following interdural dissection, which allowed for access to the inferolateral entry corridors into the lateral wall. Extradural peritrigeminal extension in the frontotemporal-orbitozygomatic and frontotemporal-zygomatic approaches allows for enlargement of the supramaxillary and pre- and postmandibular corridors. The perilabyrinthine approach to the posterior wall was enlarged with opening of Dorello's canal and the endoscopic transnasal transsphenoidal approach was enlarged with opening of the optic canal. CONCLUSIONS: Targeted extradural preparation optimizes exposure and significantly improves access to deep-seated targets by enhancing surgical maneuverability through the unlocking of neurovascular structures and widening of surgical corridors without the need for additional brain retraction.

A novel 3D surgical neuroanatomy course for medical students: Outcomes from a pilot 6-week elective.

BACKGROUND: Developing and maintaining a three-dimensional working knowledge of neuroanatomy is an essential skill in neurosurgery. However, conventional 2D head, neck, and neuroanatomy education is typically characterized by the separate rote learning of constituent tissues and often fails to provide learners with a contextual understanding of the relationships between these highly complex and interconnected structures. This can pose a significant challenge to medical students entering neurosurgery who lack a topographic understanding of intracranial anatomy. METHODS: We report on the design and efficacy of a novel 6-part 3D surgical neuroanatomy pilot elective for medical students that utilized a navigation-based pedagogical technique with the goal of providing students with a framework for developing a 3D mental map of the skull base, neurovasculature, ventricular system, and associated brain regions. Students took on the perspective of physically traveling along the paths of key structures with a 360-degree view of surrounding anatomy such that they could appreciate the integration and relative spatial relationships of the varying tissues within the cranium. Mental navigation exercises and pre- and post-course surveys were used to assess students' baseline and learned familiarity with the different anatomical regions covered. RESULTS: At the conclusion of the course, all students were able to successfully complete all of the multifaceted mental navigation exercises. Post-course survey data indicated that respondents perceived significant increases in their knowledge of cranial nerves; anterior, middle, and posterior skull base anatomy; anterior and posterior cranial circulation; and the ventricular system. CONCLUSION: 3D navigation-based fly-through instruction is a novel and effective technique for teaching complex anatomy and can provide learners with the foundational skills for developing and maintaining a 3D mental map of intracranial anatomy.

Characteristics and management of hydrocephalus associated with vestibular schwannomas: a systematic review.

Hydrocephalus (HC) can be associated with vestibular schwannoma (VS) at presentation. Although spontaneous resolution of HC after VS removal is reported, first-line treatment is varied including preoperative ventriculoperitoneal (VP) shunt, external ventricular drainage (EVD), or lumbar drainage (LD). We performed a systematic review to clarify optimal management of HC associated with VS at presentation, as well as characteristics of patients with initial and persistent HC after VS removal, and prevalence of HC associated with VS. Fourteen studies were included. Patients were grouped according to the timing of HC treatment. The overall rate of VP shunts was 19.4%. Among patients who received VS removal as first-line treatment, 6.9% underwent permanent shunts. In a subgroup of 132 patients (studies with no-aggregate data), t test analysis for mean tumor size (P = 0.02) and mean CSF protein level (P < 0.001) demonstrated statistically significant differences between patients with resolved HC (3.48 cm and 201 mg/dL) and patients with persistent HC (2.46 cm and 76.8 mg/dL) after VS resection. Transient treatment of HC using EVD or LD further resolved the HC in 87.5% and 82.9% of patients, respectively, before and after VS removal. The overall prevalence of HC associated with VS in a population of 2336 patients was 9.3%. Schwannoma removal as first-line treatment is justified by its low rate of persistent HC requiring VP shunt (roughly 7%). Patients with smaller VS and lower CSF proteins present higher risk of persistent HC after schwannoma removal. Temporary treatment of HC contributes to its resolution, both before and after VS removal.

Anterior Clinoidal Meningiomas: Meningeal Anatomical Considerations and Surgical Implications.

Objective: Surgical removal of anterior clinoidal meningiomas (ACMs) remains a challenge because of its complicated relationship with surrounding meninges, major arteries and cranial nerves. This study aims to define the meningeal structures around the anterior clinoid process (ACP) and its surgical implications. Methods: Five dry skulls and 19 cadavers were used in the anatomical study. Cadavers were prepared as transverse, coronal, and sagittal plastinated sections, and the meningeal architecture around the ACP was studied with dissecting and confocal microscopies. The database of meningiomas in one single center was retrospectively reviewed, and the patients with ACMs were collected for clinical analysis. Results: The superior, lateral, medial surfaces, and the tip of ACP were covered by different layers and types of meninges. The ACMs were classified into four main types based on the sites of origin, possible extending pathways following meningeal dura. In the retrospective cohort of 131 ACMs, the percentage of types I, IIa, IIb, III, and IV were 42.0% (55/131), 19.8% (26/131), 9.2% (12/131), 16.8% (22/131), and 12.2% (16/131), respectively. We found that types IIa and I had higher chances for achieving Simpson grade 1-2 resection (92.3 and 85.4%, respectively), followed by type III (54.5%) and type IV (31.3%), while type IIb showed little chance of Simpson grade 1-2 resection. Univariate and multivariate analyses revealed ACM classification and tumor size (<3 cm) to be independent risk factors for achieving more extensive resection. Conclusion: The meningeal architecture around the ACP may guide and determine the origin and extension of ACMs. The classification based on the meningeal architecture helps to understand surgical anatomy as well as predicting surgical outcomes.

Surgical Management of Posterior Communicating Artery Aneurysms in the Presence of a Low-Coursing Internal Carotid Artery and Narrowed Retrocarotid Window.

BACKGROUND: Anatomical variations of the course of the internal carotid artery (ICA) may complicate surgical clipping of posterior communicating artery (PCoA) aneurysms by narrowing the retrocarotid window. We evaluated the efficacy of the periclinoid surgical maneuvers for expanding the retrocarotid window and analyzed computed tomography angiography (CTA) data from patients with PCoA aneurysms to define parameters for low-coursing ICAs. METHODS: Using cadaveric specimens, standard pterional craniotomies were fashioned and extradural or intradural periclinoid surgical maneuvers-cutting of the meningo-orbital band, anterior clinoidectomy, and cutting of the distal dural ring (DDR)-were performed, and their relative advantages for expanding the retrocarotid window were assessed. Additionally, preoperative CTA data from 24 patients with PCoA aneurysms used to calculate the angles of the ICA relative to the skull base. RESULTS: Periclinoid maneuvers, especially the anterior clinoidectomy, provided additional exposure of the retrocarotid space. Cutting of the DDR allowed for partial mobilization of the ICA and widened the retrocarotid surgical window, enhancing maneuverability. The anterior clinoidectomy with cutting of the DDR allowed for enhanced exposure of the medial, middle, and posterolateral aspects of the retrocarotid space. Cutting the anterior petroclinoid fold and mobilizing cranial nerve III provided wide exposure of the lateral aspect of retrocarotid space. CONCLUSION: When clipping PCoA aneurysms in the presence of normal-coursing ICAs (approximately ≥30° ICA angle), a standard pterional craniotomy with anterior clinoidectomy and cutting of the DDR allows for substantial expansion of the retrocarotid window.

Shunt-dependent hydrocephalus after aneurysmal subarachnoid hemorrhage.

INTRODUCTION: Shunt-dependent hydrocephalus (SDHC) after aneurysmal subarachnoid hemorrhage (aSAH) is the occurrence of symptomatic ventriculomegaly requiring permanent shunt diversion. Although several studies investigated the predictors of SDHC, the role of many of these factors, as well as the prevalence of SDHC and patients' clinical outcome, remain a matter of controversy. EVIDENCE ACQUISITION: According to PRISMA guidelines we performed a systematic search looking into four databases with the purpose of clarifying the prevalence of SDHC after aSAH, the predictors of SDHC, the mortality rate and clinical outcome of patients with and without SDHC. EVIDENCE SYNTHESIS: Our analysis included 23 studies involving 22,264 patients. The overall prevalence of SDHC was 22.3% (95% CI: 17.9-26.6%). The predictors of SDHC included radiological hydrocephalus at presentation (OR 6.3, 95% CI: 2.27-17.51%), external ventricular drainage insertion (OR 5.7, 95% CI: 3.77-8.61%), high Hunt and Hess scale score (HHS 3-5: OR 3.3, 95% CI: 2.64-4.15%; HHS 4-5: OR 3.2, 95% CI: 2.4-4.2%), high Fisher grade (OR 3.1, 95% CI: 2.58-3.72%), intraventricular blood (OR 3.1, 95% CI: 2.60-3.71%), vasospasm (OR 1.9, 95% CI: 1.30-2.81%), intraparenchymal hemorrhage (OR 1.8, 95% CI: 1.2-2.78%), female gender (OR 1.3, 95% CI: 1.14-1.65%) and posterior circulation aneurysms (OR 1.4, 95% CI: 1.11-1.71%). The modality of aneurysm repair did not affect the rate of permanent shunt diversion. Patients with SDHC were more likely to be associated with a poor clinical outcome (mRS 3-6) (OR 4.3), even if mortality rate was similar between shunted and non-shunted patients (9%, 95% CI: 2-16% vs. 10.8%, 95% CI: 3.2-18.5%) (P=0.09). CONCLUSIONS: The prevalence of SDHC is 22.3%. Our analysis identified several predictors of SDHC that can assist clinicians in monitoring patients with an aSAH. Shunt dependency is not related to the treatment modality of the ruptured aneurysm, whereas the occurrence of SDHC is a predictor of poor clinical outcome.

Developing a 3D composite training model for cranial remodeling.

OBJECTIVE: Craniosynostosis correction, including cranial vault remodeling, fronto-orbital advancement (FOA), and endoscopic suturectomy, requires practical experience with complex anatomy and tools. The infrequent exposure to complex neurosurgical procedures such as these during residency limits extraoperative training. Lack of cadaveric teaching tools given the pediatric nature of synostosis compounds this challenge. The authors sought to create lifelike 3D printed models based on actual cases of craniosynostosis in infants and incorporate them into a practical course for endoscopic and open correction. The authors hypothesized that this training tool would increase extraoperative facility and familiarity with cranial vault reconstruction to better prepare surgeons for in vivo procedures. METHODS: The authors utilized representative craniosynostosis patient scans to create 3D printed models of the calvaria, soft tissues, and cranial contents. Two annual courses implementing these models were held, and surveys were completed by participants (n = 18, 5 attending physicians, 4 fellows, 9 residents) on the day of the course. These participants were surveyed during the course and 1 year later to assess the impact of this training tool. A comparable cohort of trainees who did not participate in the course (n = 11) was also surveyed at the time of the 1-year follow-up to assess their preparation and confidence with performing craniosynostosis surgeries. RESULTS: An iterative process using multiple materials and the various printing parameters was used to create representative models. Participants performed all major surgical steps, and we quantified the fidelity and utility of the model through surveys. All attendees reported that the model was a valuable training tool for open reconstruction (n = 18/18 [100%]) and endoscopic suturectomy (n = 17/18 [94%]). In the first year, 83% of course participants (n = 14/17) agreed or strongly agreed that the skin and bone materials were realistic and appropriately detailed; the second year, 100% (n = 16/16) agreed or strongly agreed that the skin material was realistic and appropriately detailed, and 88% (n = 14/16) agreed or strongly agreed that the bone material was realistic and appropriately detailed. All participants responded that they would use the models for their own personal training and the training of residents and fellows in their programs. CONCLUSIONS: The authors have developed realistic 3D printed models of craniosynostosis including soft tissues that allow for surgical practice simulation. The use of these models in surgical simulation provides a level of preparedness that exceeds what currently exists through traditional resident training experience. Employing practical modules using such models as part of a standardized resident curriculum is a logical evolution in neurosurgical education and training.

The Intracranial and Intracanalicular Optic Nerve as Seen Through Different Surgical Windows: Endoscopic Versus Transcranial.

BACKGROUND: Surgically manageable lesions involving the intracranial or intracanalicular portions of the optic nerve (cranial nerve II) can be approached through several different operative windows. Given the complex anatomy of the optic nerve and its surrounding neurovascular structures, it is essential to understand the conventional and topographic anatomy of the optic nerve from different surgical perspectives as well as its relationship with surrounding structures. We describe the intracranial and intracanalicular course of the optic nerve and present an analytical evaluation of the degree of exposure provided by several different transcranial and endoscopic surgical approaches. METHODS: Using 12 cadaveric specimens (24 sides), pterional, frontotemporal-orbital, supraorbital, unilateral subfrontal, and extended endonasal approaches were performed. The transcranial approaches were extended by removing the anterior clinoid process, unroofing the optic canal, and/or cutting the falciform ligament. The endonasal approach was extended using the transplanum transtuberculum, transmedial optic carotid recess, and transcanalicular modifications. The optic nerve was divided into proximal intracranial, distal intracranial, and intracanalicular segments, which were each divided coronally into quadrants and subquadrants, to evaluate their degree of exposure in each approach. RESULTS: The pterional approach provided 135° of exposure along the superolateral aspects of the entire intracranial optic nerve, and 225° of exposure of the intracanalicular optic nerve. The supraorbital and subfrontal approaches provided similar degrees of exposure, with 225°-270° of superolateral and superomedial exposure of the nerve along its intracranial and intracanalicular segments, depending on the approach extension used, with the subfrontal approach allowing for more medial control of the nerve. The endoscopic endonasal approach provided access to the inferior and medial quadrants of the optic nerve, allowing for 180° of exposure. CONCLUSIONS: Although the pterional approach provides the widest degree of surgical exposure of all optic nerve segments, the inferior and medial quadrants of the nerve can be adequately exposed only through an endoscopic endonasal approach. Optimal approach selection based on the intended target quadrant is essential for safe surgical exposure of the optic nerve.

Preoperative identification of the initial burr hole site in retrosigmoid craniotomies: A teaching and technical note.

BACKGROUND: When fashioning a retrosigmoid craniotomy, precise placement of the initial burr hole is crucial to avoid iatrogenic sinusal injury and to facilitate a corridor that allows for minimal cerebellar retraction. METHODS: 3D CT reconstructions of 16 cadaveric sides were used to identify and measure three discrete anatomical points. These three points and distances between them were plotted onto the surface of the skull using a digital caliper to identify the optimal burr hole location. This technique was subsequently applied in 20 clinical cases. RESULTS: Optimal burr hole placement was achieved in 87.5% of specimens and, with minor refinement, 100% of clinical cases with no significant increase in operative time. Preoperative planning took an average of 10 minutes. CONCLUSION: This technique for localizing the location of the initial retrosigmoid burr hole is a simple, safe, reliable, rapid, and inexpensive solution for surgeons who do not have regular access to neuronavigation.

On the Surgical Implications of Peritrigeminal Perforating Vessels in Microvascular Decompression.

BACKGROUND: Perforating branches arising from the superior cerebellar artery (SCA) or anterior inferior cerebellar artery (AICA) that pierces the brainstem within 5 mm of the trigeminal root may limit offending vessel transposition during microvascular decompression for trigeminal neuralgia. OBJECTIVE: To investigate the microsurgical anatomy of peritrigeminal perforators and evaluate their effect on the mobility of the SCA and AICA. Additionally, we propose strategies for mitigating the potential complications caused by the presence of short peritrigeminal perforators. METHODS: Retrosigmoid approaches and exposure of the upper cerebellopontine angle were performed on 11 cadaveric heads (22 sides). The number, origin, and course of perforators were recorded and each was classified as either type I, short straight (<3 mm); type II, long straight perforators (>3 mm); or type III, long circumflex (>3 mm). Transposition of each SCA and AICA away from trigeminal nerve was performed, and degree of mobilization was evaluated and graded. RESULTS: A total of 123 perforators were identified, of which 44 were considered peritrigeminal. Of these, 19 arose from the AICA, 18 from the SCA, and 7 from the basilar artery. Type I peritrigeminal perforators were the most common at 77.3%. Transposition or interposition of the parent vessel was not possible in 8 (47.1%) instances. CONCLUSION: Identification of inhibiting perforators is essential before performing microvascular decompression to avoid ischemic injury to the brainstem. The presence of type I perforators may necessitate extensive arachnoid dissection and use of an interpositioning technique with minimal repositioning of the offending vessel.

On-Demand Intraoperative 3-Dimensional Printing of Custom Cranioplastic Prostheses.

BACKGROUND: Currently, implantation of patient-specific cranial prostheses requires reoperation after a period for design and formulation by a third-party manufacturer. Recently, 3-dimensional (3D) printing via fused deposition modeling has demonstrated increased ease of use, rapid production time, and significantly reduced costs, enabling expanded potential for surgical application. Three-dimensional printing may allow neurosurgeons to remove bone, perform a rapid intraoperative scan of the opening, and 3D print custom cranioplastic prostheses during the remainder of the procedure. OBJECTIVE: To evaluate the feasibility of using a commercially available 3D printer to develop and produce on-demand intraoperative patient-specific cranioplastic prostheses in real time and assess the associated costs, fabrication time, and technical difficulty. METHODS: Five different craniectomies were each fashioned on 3 cadaveric specimens (6 sides) to sample regions with varying topography, size, thickness, curvature, and complexity. Computed tomography-based cranioplastic implants were designed, formulated, and implanted. Accuracy of development and fabrication, as well as implantation ability and fit, integration with exiting fixation devices, and incorporation of integrated seamless fixation plates were qualitatively evaluated. RESULTS: All cranioprostheses were successfully designed and printed. Average time for design, from importation of scan data to initiation of printing, was 14.6 min and average print time for all cranioprostheses was 108.6 min. CONCLUSION: On-demand 3D printing of cranial prostheses is a simple, feasible, inexpensive, and rapid solution that may help improve cosmetic outcomes; significantly reduce production time and cost-expanding availability; eliminate the need for reoperation in select cases, reducing morbidity; and has the potential to decrease perioperative complications including infection and resorption.