Quantitative analysis of surgical exposure and maneuverability associated with the endoscope and the microscope in the retrosigmoid and various posterior petrosectomy approaches to the petroclival region using computer tomograpy-based frameless stereotaxy. A cadaveric study

Pain Outcomes Following Endoscopic Microvascular Decompression for Trigeminal Neuralgia Based on Vascular Compression Type

Background  Arterial compression of the trigeminal nerve at the root entry zone has been the long-attributed cause of compressive trigeminal neuralgia despite numerous studies reporting distal and/or venous compression. The impact of compression type on patient outcomes has not been fully elucidated. Objective  We categorized vascular compression (VC) based on vessel and location of compression to correlate pain outcomes based on compression type. Methods  A retrospective video review of 217 patients undergoing endoscopic microvascular decompression for trigeminal neuralgia categorizing VC into five distinct types, proximal arterial compression (VC1), proximal venous compression (VC2), distal arterial compression (VC3), distal venous compression (VC4), and no VC (VC5). VC type was correlated with postoperative pain outcomes at 1 month ( n  = 179) and last follow-up (mean = 42.9 mo, n  = 134). Results  At 1 month and longest follow-up, respectively, pain was rated as "much improved" or "very much improved" in 89 69% of patients with VC1, 86.6 and 62.5% of patients with VC2, 100 and 87.5% of patients with VC3, 83 and 62.5% of patients with VC4, and 100 and 100% of patients with VC5. Multivariate analysis demonstrated VC4 as a significant negative of predictor pain outcomes at 1 month, but not longest follow-up, and advanced age as a significant positive predictor. Conclusion  The degree of clinical improvement in all types of VC was excellent, but at longest follow-up VC type was not a significant predictor out outcome. However distal venous compression was significantly associated with worse outcomes at 1 month.

The endoscopic transcanal approach to the internal auditory canal: an anatomic study

PURPOSE

The internal auditory canal (IAC) plays a key role in lateral skull base surgery. Although several approaches to the IAC have been proposed, endoscope-assisted transcanal corridors to the IAC have rarely been studied. We sought to provide a step-by-step description of the transcanal transpromontorial approach to the IAC and analyze anatomic relationships that might enhance predictability and safety of this approach.

METHODS

Ten cadaveric specimens were dissected and the extended transcanal transpromontorial approach to the IAC was established. Various morphometric measurements and anatomic landmarks were reviewed and analyzed.

RESULTS

The proposed technique proved feasible and safe in all specimens. There was no inadvertent injury to the jugular bulb or internal carotid artery. The chorda tympani, a key landmark for the mastoid segment of the facial nerve, was identified in all dissections. The spherical recess of the vestibule and middle turn of cochlea are important landmarks for identification of the labyrinthine segment of the facial nerve. Identification of all boundaries of the working area is also essential for safe access. Among various morphometric measurements, the modiolus-IAC angle (≈ 150°) proved particularly consistent; given its ease of use and low variability, we believe it could serve as a landmark for identification and subsequent dissection of the IAC.

CONCLUSIONS

The extended transcanal transpromontorial approach to the IAC is feasible and safe. Relying on anatomic landmarks to ensure preservation of the involved neurovascular structures is essential for a successful approach. The modiolus-IAC angle is a consistent, reproducible landmark for IAC identification and dissection.

Quantitative Anatomical Studies in Neurosurgery: A Systematic and Critical Review of Research Methods

BACKGROUND

The anatomy laboratory can provide the ideal setting for the preclinical phase of neurosurgical research. Our purpose is to comprehensively and critically review the preclinical anatomical quantification methods used in cranial neurosurgery.

METHODS

A systematic review was conducted following the PRISMA guidelines. The PubMed, Ovid MEDLINE, and Ovid EMBASE databases were searched, yielding 1667 papers. A statistical analysis was performed using R.

RESULTS

The included studies were published from 1996 to 2023. The risk of bias assessment indicated high-quality studies. Target exposure was the most studied feature (81.7%), mainly with area quantification (64.9%). The surgical corridor was quantified in 60.9% of studies, more commonly with the quantification of the angle of view (60%). Neuronavigation-based methods benefit from quantifying the surgical pyramid features that define a cranial neurosurgical approach and allowing post-dissection data analyses. Direct measurements might diminish the error that is inherent to navigation methods and are useful to collect a small amount of data.

CONCLUSION

Quantifying neurosurgical approaches in the anatomy laboratory provides an objective assessment of the surgical corridor and target exposure. There is currently limited comparability among quantitative neurosurgical anatomy studies; sharing common research methods will provide comparable data that might also be investigated with artificial intelligence methods.

Traditional analogue vs. three-dimensional digital visualization used in ophthalmic surgery

The visualization of the surgical process remains a topical issue in cataract surgery. The review presents the history of visualization technique in ophthalmic surgery and compares the main current analogue and 3D digital technologies. The advent of 3D imaging systems in clinical practice has helped solve many issues associated with the use of standard analogue microscopes. These issues include limited focus and field of vision, the need to use a large amount of light, which increases the risk of iatrogenic retinal phototoxicity, the surgeon's attachment to the microscope and, consequently, a high load on the surgeon's visual apparatus when using eyepieces, as well as on their back and neck muscles.

Microsurgical transcranial approaches to the posterior surface of petrosal portion of the temporal bone: quantitative analysis of surgical volumes and exposed areas

Different microsurgical transcranial approaches (MTAs) have been described to expose the posterior surface of the petrous bone (PPB). A quantitative, anatomical comparison of the most used MTAs, for specific areas of the PPB, is not available. Anatomical dissections were performed on five formalin-fixed, latex-injected cadaver heads (10 sides). Six MTAs were analyzed: Kawase approach (KWA), retrosigmoid approach (RSA), retrosigmoid approach with suprameatal extension (RSAS), retrolabyrinthine approach (RLA), translabyrinthine approach (TLA), and transcochlear approach (TCA). Surgical volumes and exposed areas of each approach were quantified with a dedicated neuronavigation system (ApproachViewer, part of GTx-Eyes II, University Health Network, Toronto, Canada) and adjuvant software (ITK-SNAP and Autodesk Meshmixer 3.5). Areas and volumes were compared using linear mixed models. TCA provided the best exposure of Trautmann's triangle and the retromeatal, suprameatal, meatal, and premeatal regions. RSAs provided the best exposure of the inframeatal region, with RSAS gaining significant exposure of the suprameatal region. KWA had the highest surgical volume, and RLA the lowest. Transpetrosal approaches offer the widest exposure of PPB proportionally to their invasiveness. Retrosigmoid approaches, which get to the studied region through a postero-lateral path, are paramount for the exposure of the inframeatal and suprameatal region and, given the adequate exposure of the remaining PPB, represent an effective approach for the cerebellopontine angle (CPA). These anatomical findings must be considered with approach-related morbidity and the pathological features in order to choose the most appropriate approach in clinical practice.

Tentorial peeling during combined petrosal approach: a cadaveric dissection

BACKGROUND

The combined petrosal approach is an excellent method to access the petroclival region but has the inherent risk of injury to the temporal lobe and Vein of Labbé. Tentorial peeling has the potential to largely eliminate these risks during the classic combined transpetrosal approach.

METHODS

Anatomical dissection of three adult injected non-formalin fixed cadaveric heads was performed. Combined petrosal approach with tentorial peeling was completed. A tentorial incision just superior and parallel to the superior petrosal sinus was made to enable peeling of the tentorium into two layers, the posterior fossa tentorial leaf (PFTL), and the temporal tentorial leaf (TTL).

RESULTS

Tentorial peeling clearly exposed the continuity between the temporal dura and the TTL as well as the continuity between the presigmoid dura and the PFTL. This enabled the creation of a large dural flap extending to the tentorial incisura, providing wide access to the petroclival region without any exposure of the temporal lobe and/or basal temporal veins. Techniques to create the dural flap without trochlear nerve injury were also explored.

CONCLUSION

The technique of tentorial peeling into two distinct layers has the potential to reduce the morbidity associated with temporal lobe retraction and venous injury. Further cadaveric studies and surgical case series are needed to validate this important surgical nuance in transpetrosal approaches.

Clinical Application of Augmented Reality in Computerized Skull Base Surgery

Cranial base tactics comprise the regulation of tiny and complicated structures in the domains of otology, rhinology, neurosurgery, and maxillofacial medical procedure. Basic nerves and veins are in the nearness of these buildings. Increased the truth is a coming innovation that may reform the cerebral basis approach by supplying vital physical and navigational facts brought together in a solitary presentation. In any case, the awareness and acknowledgment of prospective results of expanding reality frameworks in the cerebral base region are really poor. This article targets examining the handiness of expanded reality frameworks in cranial foundation medical procedures and emphasizes the obstacles that present innovation encounters and their prospective adjustments. A specialized perspective on distinct strategies used being produced of an improved realty framework is furthermore offered. The newest item offers an expansion in interest in expanded reality frameworks that may motivate more secure and practical procedures. In any case, a couple of concerns have to be cared to before that can be for the vast part fused into normal practice.

Comprehensive review of surgical microscopes: technology development and medical applications

SIGNIFICANCE

Surgical microscopes provide adjustable magnification, bright illumination, and clear visualization of the surgical field and have been increasingly used in operating rooms. State-of-the-art surgical microscopes are integrated with various imaging modalities, such as optical coherence tomography (OCT), fluorescence imaging, and augmented reality (AR) for image-guided surgery.

AIM

This comprehensive review is based on the literature of over 500 papers that cover the technology development and applications of surgical microscopy over the past century. The aim of this review is threefold: (i) providing a comprehensive technical overview of surgical microscopes, (ii) providing critical references for microscope selection and system development, and (iii) providing an overview of various medical applications.

APPROACH

More than 500 references were collected and reviewed. A timeline of important milestones during the evolution of surgical microscope is provided in this study. An in-depth technical overview of the optical system, mechanical system, illumination, visualization, and integration with advanced imaging modalities is provided. Various medical applications of surgical microscopes in neurosurgery and spine surgery, ophthalmic surgery, ear-nose-throat (ENT) surgery, endodontics, and plastic and reconstructive surgery are described.

RESULTS

Surgical microscopy has been significantly advanced in the technical aspects of high-end optics, bright and shadow-free illumination, stable and flexible mechanical design, and versatile visualization. New imaging modalities, such as hyperspectral imaging, OCT, fluorescence imaging, photoacoustic microscopy, and laser speckle contrast imaging, are being integrated with surgical microscopes. Advanced visualization and AR are being added to surgical microscopes as new features that are changing clinical practices in the operating room.

CONCLUSIONS

The combination of new imaging technologies and surgical microscopy will enable surgeons to perform challenging procedures and improve surgical outcomes. With advanced visualization and improved ergonomics, the surgical microscope has become a powerful tool in neurosurgery, spinal, ENT, ophthalmic, plastic and reconstructive surgeries.

Morphometric Study of the Posterior Fossa: Identification of Practical Parameters for Tailored Selection of Surgical Routes to the Petroclival Region

Introduction The petroclival region is an integral part of the skull base. It can harbor different pathologies and provides access to the petroclival junction and cerebellopontine angle. We present the results of the morphometric analysis of the posterior fossa and a prediction model to enable skull base surgeons to choose an optimal surgical corridor considering patient's bony anatomy.

Methods Ninety patients (14 to assess interobserver reliability) with temporal bone computed tomography were selected. Exclusion criteria included patients <18 years of age, radiographic evidence of trauma, infection, or previous surgery. The images were analyzed using OsiriX MD (Bernex, Switzerland). We recorded clival length, vertical angle, and surface area, and petroclival angle, petrous apex, and translabyrinthine corridors volume.

Results The average age was 49.5 years (55%) for males. The mean clival length and surface areas were 44.2 mm (standard deviation [SD] ± 4.1) and 8.1 cm2 (SD ± 1.3). The mean petrous apex and translabyrinthine corridors volumes were 2.2 cm3 (SD ± 0.6) and 10.1 cm3 (SD ± 3.7). The mean petroclival angle at the internal auditory canal (IAC) was 154.9 degrees (SD ± 9). The clival length correlated positively with clival surface area (rho = 0.6, p <0.05), petrous apex volume (rho = 0.3, p < 0.05), and translabyrinthine volume (rho = 0.3, p < 0.05).

Conclusion The petroclival region is complex and with high variability of surgical significance. The use of preoperative measurements of the clival length and petroclival angle as part of surgical planning that could help the surgeon to choose an optimal surgical corridor by overcoming the anatomical variability elements.

Complication Rates During Endoscopic Microvascular Decompression Surgery Are Low With or Without Petrosal Vein Sacrifice

OBJECTIVE

Endoscopic-microvascular decompression (E-MVD) is a well-described treatment for trigeminal neuralgia (TGN), but there has been debate on the safety of intraoperative sacrifice of the petrosal vein (PV) due to concern for subsequent venous insufficiency. Our objective was to investigate the risk of PV sacrifice during E-MVD in TGN and subsequent postoperative complications and pain outcomes.

METHODS

5 five-year review yielded 201 patients who underwent MVD for TGN. PV sacrifice, vascular compressive anatomy, and postoperative complications attributable to venous insufficiency were analyzed. Preoperative and postoperative pain outcomes were analyzed.

RESULTS

PV was sacrificed in 118 of 201 (59%) of patients, with 43 of 201 (21%) patients undergoing partial sacrifice versus 75 of 201 (37%) with complete sacrifice. No cases of venous infarction, cerebellar swelling, or fatal complications were noted in either cohort. Non-neurologic complications occurred in 1.69% (2 of 118) of patients with PV sacrifice and 0% (0 of 83) of patients with PV preservation. Neurologic deficits (facial palsy, conductive hearing loss, gait instability, memory deficit) occurred in equal proportions in PV preservation and sacrifice groups (2.41% vs. 1.69%) Overall, 87.3% (145 of 166) patients reported their pain as "very much improved" or "much improved" at 1 month, and no difference between groups was identified.

CONCLUSIONS

This study did not find higher complication rates in patients undergoing petrosal vein sacrifice during E-MVD for trigeminal neuralgia. In this series where petrosal vein was sacrificed only 59% of the time, it appears to be a safe technique, but larger studies will be needed to determine true incidence of complications after PV sacrifice.

Transcanal Transpromontorial Approach to Lateral Skull Base: Maximal Area of Exposure and Surgical Extensions

OBJECTIVE

To determine the possible surgical extensions and maximal area of exposure (AOE) achievable through the transcanal transpromontorial approach (TTA) to the internal auditory canal (IAC) and cerebellopontine angle. We hypothesize a possible extension of indication for this minimally invasive approach to the lateral skull base.

METHODS

In this experimental anatomic study, the expanded TTA was first carried out in 4 temporal bones to define the anatomic boundaries of the maximal exposure, from 2 perspectives, the middle ear and the porus of the IAC. Consecutively, these identified boundaries were translated on segmented 3-dimensional (3D) surface models of 32 temporal bone high-resolution computed tomography scans.

RESULTS

The dissections performed were the basis followed during the determination of the AOE on the 3D surface models. The measurements revealed that the AOE at the middle ear was 152.9 ± 33.6 mm², whereas it was 151.9 ± 24.8 mm² at the porus of the IAC. The mean superoinferior and anteroposterior extensions at the middle ear were 14.7 ± 2.5 mm and 16.9 ± 2.5 mm, respectively. On the other hand, the mean superoinferior and anteroposterior extensions at the IAC porus were 10.3 ± 1.3 mm and 18.5 ± 1.9 mm, respectively.

CONCLUSIONS

Consistent with the minimally invasive approaches, the AOE is limited; however, if compared with traditional approaches, it appears of considerable size. Our results may assist the surgeon in the selection process of the appropriate candidates for the TTA and to tailor the approach to the disease.

Quantitative Analysis of Surgical Freedom and Area of Exposure in Minimal-Invasive Transcanal Approaches to the Lateral Skull Base

HYPOTHESIS

We aim to provide objective data regarding the area of exposure (AOE) and the surgical freedom (SF) offered by the transcanal approaches to the lateral skull base.

BACKGROUND

Minimal-invasive transcanal lateral skull base procedures have been recently developed and their clinical feasibility demonstrated. The reduced access size requires careful analysis and selection of suitable cases, qualifying for a minimal-invasive approach.

METHODS

We performed the mentioned approaches in standardized dissection using human whole heads. Surgical freedom is defined as the degree of movement liberty of the surgical instrument at predefined landmarks. We assessed SF at anatomical landmarks throughout the lateral skull base. Moreover, we measured the AOE, defined as the surface on the lateral skull base reached by every approach.

RESULTS

We performed a total of 48 dissections under stereotactic image guidance in a total of 12 sides. The mean SF was assessed for the inferior petrous apex 602 mm, for the geniculate ganglion 1,916 mm, and for the fundus of internal auditory canal 1,337 mm. The AOE was measured for the infracochlear approach 55 mm, suprageniculate approach 67 mm, transpromontorial approach 11 mm, and for the expanded transpromontorial approach 93 mm at the fundus and 108 mm at the porus of the internal auditory canal.

CONCLUSION

This study provides a quantitative description of minimal-invasive transcanal approaches to the lateral skull base. The AOE offered by the expanded transcanal transpromontorial approach is inferior but comparable to the reported AOE of transmastoidal approaches. The reported objective measurements may provide important information for future preoperative planning and patient counseling.

Minimally Invasive Endoscopic Retrosigmoid Approach to the Cerebellopontine Angle Using a Novel Surgical Instrument: A Cadaveric Study

OBJECTIVES

In this study, we aimed to describe how endoscopes show the neural and vascular structures at the cerebellopontine angle (CPA) through a minimal craniotomy in a well-described anatomic point in the retrosigmoid region and at the same time, evaluate the endoscopic anatomic exposure and maneuverability. We planned to use the new surgical instrument (endoscope cannula), which we designed on fresh frozen cadavers to simulate a real surgical procedure.

MATERIALS AND METHODS

The surgical procedure was planned to be performed on 20 sides of 10 fresh cadaver heads. The distance between the asterion and mastoid process was determined, and the midpoint was then marked. From this midpoint, a craniotomy 2 cm in size was posteriorly made. The endoscope cannula together with 0° or 30° endoscopes was inserted to capture the panoramic views of the neurovascular structures in CPA. Endoscopic anatomic exposure and maneuverability were evaluated using 0° and 30° endoscopes with/without the endoscope cannula.

RESULTS

The surgeon could easily use both hands during the surgical simulation, and maneuverability was seen to increase in CPA with the use of the endoscope cannula.

CONCLUSION

The surgeon can work actively with both hands when the endoscopes and the endoscope cannula are used together. We believe that owing to this, the surgeon's maneuverability would increase and a more effective minimally invasive endoscopic retrosigmoid surgery would ensue.

Laboratory Evaluation of a Robotic Operative Microscope - Visualization Platform for Neurosurgery

Background We assessed a new robotic visualization platform with novel user-control features and compared its performance to the previous model of operative microscope. Methods In a neurosurgery research laboratory, we performed anatomical dissections and assessed robotic, exoscopic, endoscopic, fluorescence functionality. Usability and functionality were tested in the operating room over 1 year. Results The robotic microscope showed higher sensitivity for fluorescein sodium, higher detail in non-fluorescent background, and recorded/presented pictures with color quality similar to observation through the oculars. PpIX visualization was comparable to the previous microscope. Near-infrared indocyanine green imaging 3-step replay allowed for more convenient accurate assessment of blood flow. Point lock and pivot point functions were used in dissections to create 3D virtual reality microsurgical anatomy demonstrations. Pivot point control was particularly useful in deep surgical corridors with dynamic retraction. 3D exoscopic function was successfully used in brain tumor and spine cases. Endoscopic assistance was used for around-the-corner views in minimally invasive approaches. We present illustrative cases highlighting utility and new ways to control the operative microscope. Conclusion Improvements of the robotic visualization platform include intraoperative fluorescence visualization using FNa, integrated micro-inspection tool, improved ocular imaging clarity, and exoscopic mode. New robotic movements positively assist the surgeon and provide improved ergonomics and a greater level of intraoperative comfort, with the potential to increase the viewing quality. New operational modes also allow significant impact for anatomy instruction. With the increasing number and complexity of functions, surgeons should receive additional training in order to avail themselves of the advantages of the numerous novel features.

Quantification of Working Volumes, Exposure, and Target-Specific Maneuverability of the Pterional Craniotomy and Its Minimally Invasive Variants

OBJECTIVE

Quantitative comparison of minimally invasive and standard cranial approaches remains a methodologic challenge. The aim of this study was to apply a new digital, navigation-based method to quantify multiple parameters of the pterional, supraorbital, lateral supraorbital and mini-pterional approaches and to describe a target-specific maneuverability score.

METHODS

Supraorbital, lateral supraorbital, mini-pterional, and standard pterional craniotomies were performed on 8 sides in 4 cadaver heads. The limits of superficial and deep exposure and surgical target points were registered with image-guidance (Medtronic Stealth). A custom software (Guided Therapeutics Eyes II Software [GTxEyesII]) calculated superficial and deep surface areas, working volumes, and target distances. Volumes were reconstructed digitally and visualized with GTxEyesII. Finally, we defined for each approach a target-specific maneuverability score based on surface exposure, target distance, target position, and anatomical obstacles.

RESULTS

Surface exposure and volumes were significantly smaller for keyhole approaches compared with standard pterional craniotomy (P < 0.01). Maneuverability index scores showed the greatest values for standard pterional craniotomies, but nearly equally high scores could be achieved by one or several of the less-invasive approaches for most of the targets.

CONCLUSIONS

The combination of a navigation-based measurement method with custom software (GTxEyesII) provides a powerful tool for visualization and quantification of surgical approaches. Compared with standard pterional craniotomy, alternative keyhole craniotomies offer comparable deep exposure with smaller working volumes and relatively high maneuverability for specific targets.

Quantitative analysis of surgical exposure and surgical freedom to the anterosuperior pons: comparison of pterional transtentorial, orbitozygomatic, and anterior petrosal approaches

Surgical approaches to the pons lump together different areas of the pons, such as the anterosuperior and the anteroinferior pons. These areas are topographically different, and different approaches may be best suited for one or the other area. We evaluated the exposure of the anterosuperior pons using different surgical approaches. We quantify the surgical exposure and surgical freedom to the anterosuperior pons afforded by the pterional transtentorial (PT), the orbitozygomatic with anterior clinoidectomy (OZ), and the anterior petrosal (AP) approaches. Five embalmed cadaver heads were used. The three approaches were executed on each side, for a total of 30 approaches. The area of maximal exposure of the anterosuperior pons was measured with the aid of neuronavigation. We also evaluated the feasible angles of approach in the vertical and horizontal planes. We were able to successfully expose the anterosuperior pons using all the selected approaches. In the PT and OZ approaches, mobilization of the sphenoparietal sinus can prevent over-retraction of the temporal bridging veins, while use of the endoscope can help in preserving the integrity of the fourth nerve while cutting the tentorium. The mean exposure area was largest for the AP and smallest for the PT; the surgical freedom was similar among all the approaches. However, there was no statistically significant difference among all the approaches in the exposure area or in the surgical freedom. There is no significant difference among the three evaluated approaches in exposure of the anterosuperior pons.

Comparison of surgical exposure and maneuverability associated with microscopy and endoscopy in the retrolabyrinthine and transcrusal approaches to the retrochiasmatic region: a cadaveric study

BACKGROUND

The retrolabyrinthine and transcrusal approaches (RLA and TCA, respectively) are the two most often used posterior transpetrosal approaches that are used to treat lesions in the retrochiasmatic region. Endoscopes are increasingly used in neurosurgical practice. To determine whether a difference exists between the two transpetrosal approaches in the retrochiasmatic region, we evaluated and compared the exposure and maneuverability associated with the microscope and the endoscope in these approaches.

METHODS

Seven formalin-fixed cadaveric heads were dissected bilaterally through the two approaches: four for evaluation and three injected with colored latex for photography. The retrochiasmatic region was divided into four sub-compartments: the compartment before the infundibulum, which was further divided into two parts, (1) the ipsilateral and (2) the contralateral compartments; (3) the retroinfundibulum compartment; (4) the third ventricle. After each approach, exposure and maneuverability of the structures in these four compartments obtained by microscopy and endoscopy were scored under a guidance of a numerical grading system for further comparison.

RESULTS

The TCA provided better exposure and maneuverability at the retrochiasmatic region than the RLA in both the microscopy model [scores of 39.75 ± 2.12 and 32.38 ± 2.56 respectively (p < 0.05)] and the endoscopy model [scores of 82.13 ± 3.40 and 43.75 ± 1.67 respectively (p < 0.05)].

CONCLUSIONS

The TCA is better than the RLA at offering exposure and manipulation to structures in the retrochiasmatic region, especially in patients whose lesion is located high into the third ventricle and/or expanded into the contralateral part. Endoscopes may be helpful in TCA in terms of exposing and maneuvering structures in the contralateral and interpeduncle fossa areas. However, in RLA, not enough room is available for simultaneously maneuvering an endoscope and a surgical instrument.

Quantification and comparison of neurosurgical approaches in the preclinical setting: literature review

There is a growing awareness of the need for evidence-based surgery and of the issues that are specific to research in surgery. Well-conducted anatomical studies can represent the first, preclinical step for evidence-based surgical innovation and evaluation. In the last two decades, various reports have quantified and compared neurosurgical approaches in the anatomy laboratory using different methods and technology. The aim of this study was to critically review these papers. A PubMed and Scopus search was performed to select articles that quantified and compared different neurosurgical approaches in the preclinical setting. The basic characteristics that anatomically define a surgical approach were defined. Each study was analyzed for measured features and quantification method and technique. Ninety-nine papers, published from 1990 to 2013, were included in this review. A heterogeneous use of terms to define the features of a surgical approach was evident. Different methods to study these features have been reported; they are generally based on quantification of distances, angles, and areas. Measuring tools have evolved from the simple ruler to frameless stereotactic devices. The reported methods have each specific advantages and limits; a common limitation is the lack of 3D visualization and surgical volume quantification. There is a need for a uniform nomenclature in anatomical studies. Frameless stereotactic devices provide a powerful tool for anatomical studies. Volume quantification and 3D visualization of the surgical approach is not provided with most available methods.

Comparison of surgical freedom and area of exposure in three endoscopic transmaxillary approaches to the anterolateral cranial base

Objective Endoscopic ipsilateral endonasal transmaxillary, contralateral endonasal transseptal transmaxillary, and Caldwell-Luc approaches can access lesions within the retromaxillary space and pterygopalatine fossa. We compared the exposure and surgical freedom of these transmaxillary approaches to assist with surgical decision making. Design Four cadaveric heads were dissected bilaterally using the three approaches just described. Prior to dissection, stereotactic computed tomography (CT) scans were obtained on each head to obtain anatomical measurements. Surgical freedom and area of exposure were determined by stereotaxis. Main Outcome Measures Area of exposure was calculated as the extent of the orbital floor, maxillary sinus floor, nasal floor, and mandibular ramus exposed through each approach. Surgical freedom was the area through which the proximal end of the endoscope could be freely moved while moving the tip of the endoscope to the edges of the exposed area. Results The mean exposed area was similar: 9.9 ± 2.5 cm(2) (Caldwell-Luc), 10.4 ± 2.6 cm(2) (ipsilateral endonasal), and 10.1 ± 2.1 cm(2) (contralateral transseptal) (p > 0.05). The surgical freedom of the Caldwell-Luc approach (113 ± 7 cm(2)) was greater than for either endonasal approach, 76 cm(2 )± 15 (p = 0.001) (ipsilateral endonasal) and 83 cm(2) ± 15 (p = 0.003) contralateral transseptal. Conclusions Our work demonstrates that the Caldwell-Luc endonasal approach offers greater surgical freedom than either approach for anterolateral skull base targets, although these approaches offer similar exposure.

Anatomical and computed tomographic analysis of the transcochlear and endoscopic transclival approaches to the petroclival region

OBJECTIVES/HYPOTHESIS

Advances in the field of skull base surgery aim to maximize anatomical exposure while minimizing patient morbidity. The petroclival region of the skull base presents numerous challenges for surgical access due to the complex anatomy. The transcochlear approach to the region provides adequate access; however, the resection involved sacrifices hearing and results in at least a grade 3 facial palsy. An endoscopic endonasal approach could potentially avoid negative patient outcomes while providing a desirable surgical window in a select patient population.

STUDY DESIGN

Cadaveric study.

METHODS

Endoscopic access to the petroclival region was achieved through an endonasal approach. For comparison, a transcochlear approach to the clivus was performed. Different facets of the dissections, such as bone removal volume and exposed surface area, were computed using computed tomography analysis.

RESULTS

The endoscopic endonasal approach provided a sufficient corridor to the petroclival region with significantly less bone removal and nearly equivalent exposure of the surgical target, thus facilitating the identification of the relevant anatomy. The lateral approach allowed for better exposure from a posterolateral direction until the inferior petrosal sinus; however, the endonasal approach avoided labyrinthine/cochlear destruction and facial nerve manipulation while providing an anteromedial viewpoint. The endonasal approach also avoided external incisions and cosmetic deficits. The endonasal approach required significant sinonasal resection.

CONCLUSIONS

Endoscopic access to the petroclival region is a feasible approach. It potentially avoids hearing loss, facial nerve manipulation, and cosmetic damage.