"Sagittal Crest": Definition, Stepwise Dissection, and Clinical Implications From a Transorbital Perspective

Is It Time for a Paradigm Shift in the Surgical Management of Trigeminal Schwannomas? Evaluating the Role of the Transorbital Approach: An Anatomo-Clinical Study and Systematic Literature Review

BACKGROUND

Endoscopic transorbital approach emerged in recent years as an effective, minimally invasive route to access Meckel's cave area. Several case series proved its effectiveness in the surgical treatment of trigeminal schwannomas. This route provides the advantages of a minimally invasive approach associated with low morbidity rates. In this anatomo-clinical study we illustrate the usefulness of the superior eyelid transorbital approach for the surgical treatment of trigeminal schwannoma guiding the clinical applicability of the anatomical findings into real surgical practice.

METHODS

Superior eyelid transorbital endoscopic approach was performed on 8 cadaveric specimens, and the surgical results were confirmed in a retrospective review of all the surgical cases of transorbital surgery performed by the senior authors providing an illustrative case. Finally, we performed a literature review of all the case series of trigeminal schwannomas operated through an endoscopic transorbital approach.

RESULTS

Stepwise dissection was divided in 3 phases: skin, endo-orbital, and endocranial. The illustrative case provided demonstrate gross total resection of a cavernous sinus type trigeminal schwannomas treated through this route. Literature review revealed 68 cases of trigeminal schwannomas that were successfully treated using the transorbital approach.

CONCLUSIONS

The endoscopic transorbital approach may offer a valuable alternative for the surgical treatment of trigeminal schwannomas. This technique provides a minimally invasive, direct and natural "interdural" route to the lateral wall of the cavernous sinus and Meckel's cave.

Neurophysiologic Monitoring of Oculomotor Nerves During Transorbital Surgery: Proof of Concept and Anatomic Demonstration

BACKGROUND AND OBJECTIVES

Transorbital neuroendoscopic surgery (TONES) is continuously evolving and gaining terrain in approaching different skull base pathologies. The objective of this study was to present our methodology for introducing recording electrodes, which includes a new transconjunctival pathway, to monitor the extraocular muscle function during TONES.

METHODS

A translational observational study was performed from an anatomic demonstration focused on the transconjunctival electrode placement technique to a descriptive analysis in our series of 6 patients operated using TONES in association with intraoperative neurophysiologic monitoring of the oculomotor nerves from 2017 to 2023. The stepwise anatomic demonstration for the electrode placement and correct positioning in the target muscle was realized through cadaveric dissection. The descriptive analysis evaluated viability (obtention of the electromyography in each cranial nerve [CN] monitored), security (complications), and compatibility (interference with TONES).

RESULTS

In our series of 6 patients, 16 CNs were correctly monitored: 6 (100%) CNs III, 5 (83.3%) CNs VI, and 5 (83.3%) CNs IV. Spontaneous electromyography was registered correctly, and compound muscle action potential using triggered electromyography was obtained for anatomic confirmation of structures (1 CN III and VI). No complications nor interference with the surgical procedure were detected.

CONCLUSION

The methodology for introducing the recording electrodes was viable, secure, and compatible with TONES.

Biportal Endoscopic TransOrbital and transMaxillary Approach to the Cranio-Orbital Region and Middle Cranial Fossa: A Preliminary Analysis of Maneuverability

BACKGROUND AND OBJECTIVES

Traditional and well-established transcranial approaches to the spheno-orbital region and middle cranial fossa guarantee optimal intracranial exposure, and additional orbital and zygomatic osteotomies provide further control over extracranial components to be resected; however, these techniques come at the cost of additional morbidity. The introduction of minimally invasive endoscopic approaches and the conceptualization of the so-called "multiportal" paradigm might provide an alternative route. This preliminary study investigates the feasibility of the combined Biportal Endoscopic TransOrbital and transMaxillary Approach (bETOMA) approach to the spheno-orbital and middle cranial fossa regions.

METHODS

Using 4 silicon-injected adult cadaver heads (8 sides; 16 approaches), we systematically dissected through superior eyelid ETOA and endoscopic TMA approaches. The analysis focused on pterygopalatine, infratemporal, anterior and middle cranial fossae, Meckel cave, and cavernous sinus access. We evaluated the feasibility of bETOMA using linear distances, angles of attack, and exposure areas. We also introduced volume of operative maneuverability, its standardized derivative (sVOM), target distance, visuo-operative angle, and working zone volume as novel metrics.

RESULTS

The analysis revealed comparable angles of attack between approaches. ETOA and TMA exposure areas were 918.38 ± 223.93 mm2 and 257.07 ± 86.07 mm2, respectively. TMA showed a larger VOM in the greater sphenoid wing, but ETOA offered superior distal maneuverability (sVOM: 5.39 ± 1.94 vs 2.54 ± 0.79 cm3) and closer intracranial space access (27.45 vs 50.83 mm). The combined approaches yielded a mean working zone volume of 13.75 ± 3.73 cm3 in the spheno-orbital interface.

CONCLUSION

The bETOMA approach provides adequate neurovascular exposure and maneuverability to the spheno-orbital region, infratemporal, and anterior and middle cranial fossae, addressing significant limitations of previously investigated monoportal techniques (ie, optic nerve decompression, hyperostotic bone resection, and infratemporal exposure). This combined minimally invasive approach might help manage lesions harbored within the cranio-orbital interface region invading the extracranial space.

Navigating the Intersection Between the Orbit and the Skull Base: The "Mirror" McCarty Keyhole During Transorbital Approach: An Anatomic Study With Surgical Implications

BACKGROUND AND OBJECTIVES

McCarty keyhole (MCK) is the most important entry point during orbitocranial and cranio-orbital approaches; nevertheless, its anatomic coordinates have never been detailedly described from transorbital perspective. To provide the spatial coordinates for intraorbital projection of the "mirror" MCK by using the well-established main anatomic-surgical bony landmarks met along transorbital corridor.

METHODS

MCK was identified in 15 adult dry skulls (30 sides) on exocranial surface of pterional region based on the well-defined external bony landmarks: on the frontosphenoid suture, 5 to 6 mm behind the joining point (JP) of frontozygomatic suture (FZS), frontosphenoid suture (FSS), and sphenozygomatic suture (SZS). A 1-mm burr hole was performed and progressively enlarged to identify the intracranial and intraorbital compartments. Exit site of the intraorbital part of burr hole was referenced to the FZS on the orbital rim, the superior orbital fissure, and the inferior orbital fissure and to the JP of FZS, FSS, and SZS. To electronically validate the results, 3-dimensional photorealistic and interactive models were reconstructed with photogrammetry. Finally, for a further validation, McCarty mirror keyhole was also exposed, based on results achieved, through endoscopic transorbital approach in 10 head specimens (20 sides).

RESULTS

Intraorbital projection of MCK was identified on the FSS on intraorbital surface, 1.5 ± 0.5 mm posterior to JP, 11.5 ± 1.1 mm posterior to the FZS on orbital rim following the suture, 13.0 ± 1.2 mm from most anterior end of superior orbital fissure, 15.5 ± 1.4 mm from the most anterior end of the inferior orbital fissure in vertical line, on measurements under direct macroscopic visualization (mean ± SD). These values were electronically confirmed on the photogrammetric models with mean difference within 1 mm.

CONCLUSION

To be aware of exact position of intraorbital projection of MCK during an early stage of transorbital approaches provides several surgical, clinical, and aesthetic advantages.

Endoscopic Transorbital Resection of Temporal Pole Cavernoma: 2-Dimensional Operative Video

An endoscopic transorbital approach has been recently included in the neurosurgical armamentarium.1 We present a case of a 31-year-old female patient with a history of recent-onset refractory epilepsy related to a left temporal pole cavernoma operated through a superior eyelid endoscopic transorbital approach. The operative video shows the key surgical steps to ensure optimal surgical freedom, adequate exposure, and complete tumor resection.2 The postoperative course was uneventful, and the patient obtained seizure control and good cosmetic results without postoperative complications. The brain computed tomography and MRI showed the size of bone removal and confirmed the complete removal of the lesion, respectively. At 3-month follow-up, the patient is epileptic seizures-free without medications. An endoscopic transorbital approach provides adequate exposure of the temporal pole, allowing safe tumor resection. Complication avoidance encompasses careful dissection of palpebral muscles, dynamic orbital retraction, and neuronavigation guidance; sphenoidal drilling according to key anatomic landmarks (eg, sagittal crest3); and anatomic knowledge of the cavernous sinus and internal carotid artery and its tributaries course from a transorbital perspective4 and reconstruction filling the empty spaces using fat, fascia lata, or dural substitutes. All procedures performed were approved by the ethics committee of both centers and in accordance with Declaration of Helsinki and its later amendments. The patient consented to the procedure and to the publication of her images, and appropriate consent was obtained for publication of cadaveric images.

The Transorbital Approach: A Comprehensive Review of Targets, Surgical Techniques, and Multiportal Variants

The transorbital approach (TOA) is gaining popularity in skull base surgery scenarios. This approach represents a valuable surgical corridor to access various compartments and safely address several intracranial pathologies, both intradurally and extradurally, including tumors of the olfactory groove in the anterior cranial fossa (ACF), cavernous sinus in the middle cranial fossa (MCF), and the cerebellopontine angle in the posterior cranial fossa (PCF). The TOA exists in many variants, both from the point of view of invasiveness and from that of the entry point to the orbit, corresponding to the four orbital quadrants: the superior eyelid crease (SLC), the precaruncular (PC), the lateral retrocanthal (LRC), and the preseptal lower eyelid (PS). Moreover, multiportal variants, consisting of the combination of the transorbital approach with others, exist and are relevant to reach peculiar surgical territories. The significance of the TOA in neurosurgery, coupled with the dearth of thorough studies assessing its various applications and adaptations, underscores the necessity for this research. This extensive review delineates the multitude of target lesions reachable through the transorbital route, categorizing them based on surgical complexity. Furthermore, it provides an overview of the different transorbital variations, both standalone and in conjunction with other techniques. By offering a comprehensive understanding, this study aims to enhance awareness and knowledge regarding the current utility of the transorbital approach in neurosurgery. Additionally, it aims to steer future investigations toward deeper exploration, refinement, and exploration of additional perspectives concerning this surgical method.

Transorbital approach to the cavernous sinus: an anatomical study of the related cranial nerves

Background

The cavernous sinus (CS) is a demanding surgical territory, given its deep location and the involvement of multiple neurovascular structures. Subjected to recurrent discussion on the optimal surgical access, the endoscopic transorbital approach has been recently proposed as a feasible route for selected lesions in the lateral CS. Still, for this technique to safely evolve and consolidate, a comprehensive anatomical description of involved cranial nerves, dural ligaments, and arterial relations is needed.

Objective

Detailed anatomical description of the CS, the course of III, IV, VI, and V cranial nerves, and C3-C7 segments of the carotid artery, all described from the ventrolateral endoscopic transorbital perspective.

Methods

Five embalmed human cadaveric heads (10 sides) were dissected. An endoscopic transorbital approach with lateral orbital rim removal, anterior clinoidectomy, and petrosectomy was performed. The course of the upper cranial nerves was followed from their apparent origin in the brainstem, through the middle fossa or cavernous sinus, and up to their entrance to the orbit. Neuronavigation was used to follow the course of the nerves and to measure their length of surgical exposure.

Results

The transorbital approach allowed us to visualize the lateral wall of the CS, with cranial nerves III, IV, V1-3, and VI. Anterior clinoidectomy and opening of the frontal dura and the oculomotor triangle revealed the complete course of the III nerve, an average of 37 (±2) mm in length. Opening the trigeminal pore and cutting the tentorium permitted to follow the IV nerve from its course around the cerebral peduncle up to the orbit, an average of 54 (±4) mm. Opening the infratrochlear triangle revealed the VI nerve intracavernously and under Gruber's ligament, and the extended petrosectomy allowed us to see its cisternal portion (27 ± 6 mm). The trigeminal root was completely visible and so were its three branches (46 ± 2, 34 ± 3, and 31 ± 1 mm, respectively).

Conclusion

Comprehensive anatomic knowledge and extensive surgical expertise are required when addressing the CS. The transorbital corridor exposes most of the cisternal and the complete cavernous course of involved cranial nerves. This anatomical article helps understanding relations of neural, vascular, and dural structures involved in the CS approach, essential to culminating the learning process of transorbital surgery.

Endoscopic transorbital decompression for traumatic superior orbital fissure syndrome: from cadaveric study to clinical application

PURPOSE

The endoscopic endonasal approach (EEA) is a minimally invasive and promising modality for treating traumatic superior orbital fissure (SOF) syndrome (tSOFS). Recently, the endoscopic transorbital approach (ETOA) has been considered an alternative method for reaching the anterolateral skull base. This study accessed the practicality of using the ETOA to treat SOF decompression using both cadaveric dissection and clinical application.

METHODS

Bilateral anatomic dissections were performed on four adult cadaveric heads using the ETOA and EEA to address SOF decompression. The ETOA procedure for SOF decompression is described, and the extent of SOF decompression was compared between the ETOA and EEA. The clinical feasibility of the ETOA for treating SOF decompression was performed in two patients diagnosed with tSOFS.

RESULTS

ETOA allowed for decompression over the lateral aspect of the SOF, from the meningo-orbital band superolaterally to the maxillary strut inferomedially. By contrast, the EEA allowed for decompression over the medial aspect of the SOF, from the lateral opticocarotid recess superiorly to the maxillary strut inferiorly. In both patients treated using the ETOA and SOF decompression, the severity of ophthalmoplegia got obvious improvement.

CONCLUSIONS

Based on the cadaveric findings, ETOA provided a feasible access pathway for SOF decompression with reliable outcomes, and our patients confirmed the clinical efficacy of the ETOA for managing tSOFS.

Transorbital Exposure of the Internal Carotid Artery: A Detailed Anatomic and Quantitative Roadmap for Safe Successful Surgery

BACKGROUND AND OBJECTIVES

The superior eyelid endoscopic transorbital approach has rapidly gained popularity among neurosurgeons for its advantages in the treatment, in a minimally invasive fashion, of a large variety of skull base pathologies. In this study, an anatomic description of the internal carotid artery (ICA) is provided to identify risky zones related to lesions that may be approached using this technique. In this framework, a practical roadmap can help the surgeon to avoid potentially life-threatening iatrogenic vascular injuries.

METHODS

Eight embalmed adult cadaveric specimens (16 sides) injected with a mixture of red latex and iodinate contrast underwent superior eyelid transorbital endoscopic approach, followed by interdural dissection of the cavernous sinus, extradural anterior clinoidectomy, and anterior petrosectomy, to expose the entire "transorbital" pathway of the ICA. Furthermore, the distance of each segment of the ICA explored by means of the superior eyelid endoscopic transorbital approach was quantitatively analyzed using a neuronavigation system.

RESULTS

We exposed 4 distinct ICA segments and named the anatomic window in which they are displayed in accordance with the cavernous sinus triangles distribution of the middle cranial fossa: (1) clinoidal (Dolenc), (2) infratrochlear (Parkinson), (3) anteromedial (Mullan), and (4) petrous (Kawase). Critical anatomy and key surgical landmarks were defined to further identify the main danger zones during the different steps of the approach.

CONCLUSION

A detailed knowledge of the reliable surgical landmarks of the course of the ICA as seen through an endoscopic transorbital route and its relationship with the cranial nerves are essential to perform a safe and successful surgery.

The Endoscopic Lateral Transorbital Approach for the Removal of Select Sphenoid Wing and Middle Fossa Meningiomas. Surgical Technique and Short-Term Outcomes

BACKGROUND AND OBJECTIVE

The endoscopic lateral transorbital approach (eLTOA) is a relatively new approach to the skull base that has only recently been applied in vivo in the management of complex skull base pathology. Most meningiomas removed with this approach have been in the spheno-orbital location. We present a series of select purely sphenoid wing and middle fossa meningiomas removed through eLTOA. The objective here was to describe the selection criteria and results of eLTOA for a subset of sphenoid wing and middle fossa meningiomas.

METHODS

This is a retrospective study based on a prospectively maintained database of consecutive cases of eLTOA operated on at our institution by the lead author. The cohort's clinical and radiographic characteristics and outcome are presented.

RESULTS

Five patients underwent eLTOA to remove 3 sphenoid wing and 2 middle fossa meningiomas. The mean tumor volume was 11.9 cm 3 . Gross total resection was achieved in all cases. There were no intraoperative complications. Postoperatively, there was one case of subretinal hemorrhage, which was corrected by open vitrectomy repair, and one case of cerebrospinal fluid leak, which resolved with lumbar drainage. Three patients presented with visual impairment, 1 improved, 1 remained stable, and 1 worsened, but returned to stable after vitrectomy repair. All patients have been free of disease at a median follow-up of 8.9 months.

CONCLUSION

eLTOA provides a direct minimal access corridor to certain well-selected sphenoid wing and middle fossa meningiomas. eLTOA minimizes brain retraction and provides a high rate of gross total resection. Meningiomas appropriately selected based on size, type, and location of dural attachment, and the eLTOA is a safe, rapid, and highly effective procedure with acceptable morbidity.

Transorbital Route to Intracranial Space

The endoscopic superior eyelid transorbital approach has emerged as a notable and increasingly utilized surgical technique in recent years. This chapter presents an overview of the approach, tracing its historical development and highlighting its growing acceptance within the skull base community.Beginning with an introduction and historical perspective, the chapter outlines the evolution of the transorbital approach, shedding light on its origins and the factors driving its adoption. Subsequently, a comprehensive exploration of the anatomic bone pillars and intracranial spaces accessible via this approach is provided. Hence, five bone pillars of the transorbital approach were identified, namely the lesser sphenoid wing, the anterior clinoid, the sagittal crest, the middle cranial fossa, and the petrous apex. A detailed correlation of those bone targets with respective intracranial areas has been reported.Furthermore, the chapter delves into the practical application of the technique through a case example, offering insights into its clinical utility, indications, and limitations.

Transorbital and supraorbital uniportal multicorridor approach to the orbit, anterior, middle and posterior cranial fossa: Anatomic study

Introduction

The transorbital route has been proposed for addressing orbital and paramedian skull base lesions. It can be complemented by further marginotomies, as per "extended-transorbital approach" and combined with others ventro-basal approaches featuring the concept of "multiportal surgery". Nevertheless, it cannot address some anatomical regions like the clinoid, carotid bifurcation and the Sylvian fissure. Therefore, we propose a combined transorbital and a supraorbital approach, attainable by a single infra-brow incision, and we called it "Uniportal multicorridor" approach.

Research question

The aim of our study is to verify its feasibility and deep anatomical targets through a cadaveric study.

Materials and methods

Anatomic dissections were performed at the Laboratory of ICLO Teaching and Research Center (Verona, Italy) on four formalin-fixed cadaveric heads injected with colored neoprene latex (8 sides). A stepwise dissection of the supraorbital and transorbital approaches (with an infra-brow skin incision) to the anterior tentorial incisura, clinoid area, lateral wall of the cavernous sinus, middle temporal fossa, posterior fossa, and Sylvian fissure is described.

Results

We analyzed the anatomic areas reached by the transorbital corridor dividing them as follow: lateral wall of the cavernous sinus, middle temporal fossa, posterior fossa, and Sylvian fissure; while the anatomic areas addressed by the supraorbital craniotomy were the clinoid area and the anterior tentorial incisura.

Conclusions

The described uniportal multi-corridor approach combines a transorbital corridor and a supraorbital craniotomy, providing a unique intra and extradural control over the anterior, middle, and posterior fossa, tentorial incisura and the Sylvian fissure, via an infra-brow skin incision.

The Transorbital Approach, A Game-Changer in Neurosurgery: A Guide to Safe and Reliable Surgery Based on Anatomical Principles

During the last few years, the superior eyelid endoscopic transorbital approach has been proposed as a new minimally invasive pathway to access skull base lesions, mostly in ophthalmologic, otolaryngologic, and maxillofacial surgeries. However, most neurosurgeons performing minimally invasive endoscopic neurosurgery do not usually employ the orbit as a surgical corridor. The authors undertook this technical and anatomical study to contribute a neurosurgical perspective, exploring the different possibilities of this novel route. Ten dissections were performed on ten formalin-fixed specimens to further refine the transorbital technique. As part of the study, the authors also report an illustrative transorbital surgery case to further detail key surgical landmarks. Herein, we would like to discuss equipment, key anatomical landmarks, and surgical skills and stress the steps and details to ensure a safe and successful procedure. We believe it could be critical to promote and encourage the neurosurgical community to overcome difficulties and ensure a successful surgery by following these key recommendations.

Lateral Transorbital Endoscope-Assisted Approach to the Cavernous Sinus

BACKGROUND AND OBJECTIVES

Surgical access to the cavernous sinus (CS) poses a unique challenge to the neurosurgeon given the concentration of delicate structures in the confines of a very small anatomic space. The lateral transorbital approach (LTOA) is a minimally invasive, keyhole approach that can provide direct access to the lateral CS.

METHODS

A retrospective review of CS lesions treated by a LTOA at a single institution was performed between 2020 and 2023. Patient indications, surgical outcomes, and complications are described.

RESULTS

Six patients underwent a LTOA for a variety of pathologies including a dermoid cyst, schwannoma, prolactinoma, craniopharyngioma, and solitary fibrous tumor. The goals of surgery (ie, drainage of cyst, debulking, and pathological diagnosis) were achieved in all cases. The mean extent of resection was 64.6% (±34%). Half of the patients with preoperative cranial neuropathies (n = 4) improved postoperatively. There were no new permanent cranial neuropathies. One patient had a vascular injury repaired endovascularly with no neurological deficits.

CONCLUSION

The LTOA provides a minimal access corridor to the lateral CS. Careful case selection and reasonable goals of surgery are critical to successful outcome.

Endoscopic transorbital resection of the temporal lobe: anatomic qualitative and quantitative study

Objective

Starting from an anatomic study describing the possibility of reaching the temporal region through an endoscopic transorbital approach, many clinical reports have now demonstrated the applicability of this strategy when dealing with intra-axial lesions. The study aimed to provide both a qualitative anatomic description of the temporal region, as seen through a transorbital perspective, and a quantitative analysis of the amount of temporal lobe resection achievable via this route.

Material and methods

A total of four cadaveric heads (eight sides) were dissected at the Laboratory of Surgical Neuroanatomy (LSNA) of the University of Barcelona, Spain. A stepwise description of the resection of the temporal lobe through a transorbital perspective is provided. Qualitative anatomical descriptions and quantitative analysis of the amount of the resection were evaluated by means of pre- and post-dissection CT and MRI scans, and three-dimensional reconstructions were made by means of BrainLab®Software.

Results

The transorbital route gives easy access to the temporal region, without the need for extensive bone removal. The resection of the temporal lobe proceeded in a subpial fashion, mimicking what happens in a surgical scenario. According to our quantitative analysis, the mean volume removed was 51.26%, with the most superior and lateral portion of the temporal lobe being the most difficult to reach.

Conclusion

This anatomic study provides qualitative and quantitative details about the resection of the temporal lobe via an endoscopic transorbital approach. Our results showed that the resection of more than half of the temporal lobe is possible through this surgical corridor. While the anterior, inferior, and mesial portions of the temporal lobe were easily accessible, the most superior and lateral segment was more difficult to reach and resect. Our study serves as an integration to the current anatomic knowledge and clinical practice knowledge highlighting and also as a starting point for further anatomic studies addressing more selected segments of the temporal lobe, i.e., the mesial temporal region.

Surgical Anatomy of the Microscopic and Endoscopic Transorbital Approach to the Middle Fossa and Cavernous Sinus: Anatomo-Radiological Study with Clinical Applications

BACKGROUND

The transorbital approaches (TOAs) have acquired growing notoriety, thanks to their ability to offer alternative corridors to the skull base. However, the limited access and the unfamiliarity with this surgical perspective make recognition of key landmarks difficult, especially for less experienced surgeons. The study wants to offer a detailed description of the anatomy to comprehend the potential and limitations of TOAs.

METHODS

Measurements of the orbit region and the surrounding areas were performed on two hundred high-resolution CT scans and thirty-nine dry skulls. Five specimens were dissected to illustrate the TOA, and one was used to perform the extradural clinoidectomy. Three clinical cases highlighted the surgical applications.

RESULTS

A step-by-step description of the key steps of the TOA was proposed and a comparison with the transcranial anterior clinoidectomy was discussed. The mean work distance was 6.1 ± 0.4 cm, and the lateral working angle increased 20 ± 5.4° after removing the lateral orbital rim.

CONCLUSIONS

TOAs are indicated in selected cases when tumor involves the lateral portion of the cavernous sinus or the middle skull base, obtaining a direct decompression of the optic nerve and avoiding excessive manipulation of the neurovascular structures. Comprehension of surgical anatomy of the orbit and its surrounding structures is essential to safely perform these approaches.

The anterolateral triangle as window on the foramen lacerum from transorbital corridor: anatomical study and technical nuances

OBJECTIVE

Neurosurgical indications for the superior eyelid transorbital endoscopic approach (SETOA) are rapidly expanding over the last years. Nevertheless, as any new technique, a detailed knowledge of the anatomy of the surgical target area, the operative corridor, and the specific surgical landmark from this different perspective is required for a safest and successful surgery. Therefore, the aim of this study is to provide, through anatomical dissections, a detailed investigation of the surgical anatomy revealed by SETOA via anterolateral triangle of the middle cranial fossa. We also sought to define the relevant surgical landmarks of this operative corridor.

METHODS

Eight embalmed and injected adult cadaveric specimens (16 sides) underwent dissection and exposure of the cavernous sinus and middle cranial fossa via superior eyelid endoscopic transorbital approach. The anterolateral triangle was opened and its content exposed. An extended endoscopic endonasal trans-clival approach (EEEA) with exposure of the cavernous sinus content and skeletonization of the paraclival and parasellar segments of the internal carotid artery (ICA) was also performed, and the anterolateral triangle was exposed. Measurements of the surface area of this triangle from both surgical corridors were calculated in three head specimens using coordinates of its borders under image-guide navigation.

RESULTS

The drilling of the anterolateral triangle via SETOA unfolds a space that can be divided by the course of the vidian nerve into two windows, a wider "supravidian" and a narrower "infravidian," which reveal different anatomical corridors: a "medial supravidian" and a "lateral supravidian," divided by the lacerum segment of the ICA, leading to the lower clivus, and to the medial aspect of the Meckel's cave and terminal part of the horizontal petrous ICA, respectively. The infravidian corridor leads medially into the sphenoid sinus. The arithmetic means of the accessible surface area of the anterolateral triangle were 45.48 ± 3.31 and 42.32 ± 2.17 mm2 through transorbital approach and endonasal approach, respectively.

CONCLUSION

SETOA can be considered a minimally invasive route complementary to the extended endoscopic endonasal approach to the anteromedial aspect of the Meckel's cave and the foramen lacerum. The lateral loop of the trigeminal nerve represents a reliable surgical landmark to localize the lacerum segment of the ICA from this corridor. Nevertheless, as any new technique, a learning curve is needed, and the clinical feasibility should be proven.

Through the orbit and beyond: Current state and future perspectives in endoscopic orbital surgery on behalf of the EANS frontiers committee in orbital tumors and the EANS skull base section

Introduction

Orbital surgery has always been disputed among specialists, mainly neurosurgeons, otorhinolaryngologists, maxillofacial surgeons and ophthalmologists. The orbit is a borderland between intra- and extracranial compartments; Krönlein's lateral orbitotomy and the orbitozygomatic infratemporal approach are the historical milestones of modern orbital-cranial surgery.

Research question

Since its first implementation, endoscopy has significantly impacted neurosurgery, changing perspectives and approaches to the skull base. Since its first application in 2009, transorbital endoscopic surgery opened the way for new surgical scenario, previously feasible only with extensive tissue dissection.

Material and methods

A PRISMA based literature search was performed to select the most relevant papers on the topic.

Results

Here, we provide a narrative review on the current state and future trends in endoscopic orbital surgery.

Discussion and conclusion

This manuscript is a joint effort of the EANS frontiers committee in orbital tumors and the EANS skull base section.

A New Perspective on the Cavernous Sinus as Seen through Multiple Surgical Corridors: Anatomical Study Comparing the Transorbital, Endonasal, and Transcranial Routes and the Relative Coterminous Spatial Regions

Background: The cavernous sinus (CS) is a highly vulnerable anatomical space, mainly due to the neurovascular structures that it contains; therefore, a detailed knowledge of its anatomy is mandatory for surgical unlocking. In this study, we compared the anatomy of this region from different endoscopic and microsurgical operative corridors, further focusing on the corresponding anatomic landmarks encountered along these routes. Furthermore, we tried to define the safe entry zones to this venous space from these three different operative corridors, and to provide indications regarding the optimal approach according to the lesion's location. Methods: Five embalmed and injected adult cadaveric specimens (10 sides) separately underwent dissection and exposure of the CS via superior eyelid endoscopic transorbital (SETOA), extended endoscopic endonasal transsphenoidal-transethmoidal (EEEA), and microsurgical transcranial fronto-temporo-orbito-zygomatic (FTOZ) approaches. The anatomical landmarks and the content of this venous space were described and compared from these surgical perspectives. Results: The oculomotor triangle can be clearly exposed only by the FTOZ approach. Unlike EEEA, for the exposure of the clinoid triangle content, the anterior clinoid process removal is required for FTOZ and SETOA. The supra- and infratrochlear as well as the anteromedial and anterolateral triangles can be exposed by all three corridors. The most recently introduced SETOA allowed for the exposure of the entire lateral wall of the CS without entering its neurovascular structures and part of the posterior wall; furthermore, thanks to its anteroposterior trajectory, it allowed for the disclosure of the posterior ascending segment of the cavernous ICA with the related sympathetic plexus through the Mullan's triangle, in a minimally invasive fashion. Through the anterolateral triangle, the transorbital corridor allowed us to expose the lateral 180 degrees of the Vidian nerve and artery in the homonymous canal, the anterolateral aspect of the lacerum segment of the ICA at the transition zone from the petrous horizontal to the ascending posterior cavernous segment, surrounded by the carotid sympathetic plexus, and the medial Meckel's cave. Conclusions: Different regions of the cavernous sinus are better exposed by different surgical corridors. The relationship of the tumor with cranial nerves in the lateral wall guides the selection of the approach to cavernous sinus lesions. The transorbital endoscopic approach can be considered to be a safe and minimally invasive complementary surgical corridor to the well-established transcranial and endoscopic endonasal routes for the exposure of selected lesions of the cavernous sinus. Nevertheless, peer knowledge of the anatomy and a surgical learning curve are required.

Endoscopic Transorbital Approach for the Management of Spheno-Orbital Meningiomas: Literature Review and Preliminary Experience

OBJECTIVE

The endoscopic transorbital approach (ETOA) is a minimally invasive approach that could be particularly appropriate for management of spheno-orbital meningiomas. The aim of this study was to perform a systematic review of the literature on the management of spheno-orbital meningiomas via the minimally invasive ETOA, searching for clinical scenarios in which this approach could be best indicated. A secondary aim was to describe 4 illustrative cases.

METHODS

A systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Data including patient demographics, tumor features, and surgical and postoperative outcomes were collected. Cases from our initial experience with ETOA were included in the data.

RESULTS

Data of 58 patients from 9 selected records and from our surgical series were collected. Subtotal, near-total, and gross total resection rates were 44.8%, 10.3%, and 32.7%, respectively. Symptom improvement after surgery was 100% for proptosis, 93% for visual impairment, and 87% for ophthalmoplegia. The most common postoperative complications were transient ophthalmoplegia and maxillary nerve hypoesthesia. Cerebrospinal fluid leak was reported in 2 patients.

CONCLUSIONS

Our findings support the use of the ETOA for management of spheno-orbital meningiomas, particularly in at least 3 clinical scenarios: 1) when predominant hyperostotic bone is present; 2) when a globular tumor not showing excessive medial or inferior infiltration is being treated; 3) as part of a multistage treatment for diffuse lesions.

TransOrbital NeuroEndoscopic Surgery for Biopsy of the Left Cavernous Sinus: A Literature Review, Case Report, and Cadaveric Proof of Concept

The aim of this report is to describe TransOrbital NeuroEndoscopic Surgery (TONES) as a safe alternative for obtaining a cavernous sinus (CS) biopsy. We describe this technique in a patient with a diffuse large B cell lymphoma mimicking Tolosa-Hunt's syndrome. Articles were gathered querying PubMed, Embase, and Scopus databases with terms related to a "transorbital neuroendoscopic approach." The literature search was performed by two independent authors (N.L.F. and J.R.), with inconsistencies resolved by the senior author (M.M.D.V.). After screening abstracts for relevance, full-length articles were reviewed for pertinent variables. A comparison was conducted with the illustrative case of a 69-year-old woman who presented to the emergency department with vertigo, ophthalmoplegia, and diplopia for 2 months. A brain magnetic resonance imaging revealed an infiltrative lesion at the left CS. A presumptive diagnosis of Tolosa-Hunt syndrome was made, but a confirmatory biopsy was performed using TONES. Based on our cadaveric study, literature review, and case report, the TONES approach was safe, effective for tissue diagnosis, and associated with minor morbidity and reduced hospital stay. Additional prospective studies are required to study its viability and safety in a larger group of patients.

The feasibility of three port endonasal, transorbital, and sublabial approach to the petroclival region: neurosurgical audit and multiportal anatomic quantitative investigation

PURPOSE

The petroclival region represents the "Achille's heel" for the neurosurgeons. Many ventral endoscopic routes to this region, mainly performed as isolated, have been described. The aim of the present study is to verify the feasibility of a modular, combined, multiportal approach to the petroclival region to overcome the limits of a single approach, in terms of exposure and working areas, brain retraction and manipulation of neurovascular structures.

METHODS

Four cadaver heads (8 sides) underwent endoscopic endonasal transclival, transorbital superior eyelid and contralateral sublabial transmaxillary-Caldwell-Luc approaches, to the petroclival region. CT scans were obtained before and after each approach to rigorously separate the contribution of each osteotomy and subsequentially to build a comprehensive 3D model of the progressively enlarged working area after each step.

RESULTS

The addition of the contralateral transmaxillary and transorbital corridors to the extended endoscopic endonasal transclival in a combined multiportal approach provides complementary paramedian trajectories to overcome the natural barrier represented by the parasellar and paraclival segments of the internal carotid artery, resulting in significantly greater area of exposure than a pure endonasal midline route (8,77 cm² and 11,14 cm² vs 4,68 cm² and 5,83cm², extradural and intradural, respectively).

CONCLUSION

The use of different endoscopic "head-on" trajectories can be combined in a wider multiportal extended approach to improve the ventral route to the most inaccessible petroclival regions. Finally, by combining these approaches and reiterating the importance of multiportal strategy, we quantitatively demonstrate the possibility to reach "far away" paramedian petroclival targets while preserving the neurovascular structures.

Multiportal Combined Endoscopic Endonasal and Transorbital Pathways: Qualitative and Quantitative Anatomic Studies of the "Connection" Skull Base Areas

BACKGROUND

Combined endonasal and transorbital multiportal surgery has been recently described for selected skull base pathologies. Nevertheless, a detailed anatomic description and a quantitative comprehensive anatomic study of the skull base areas where these 2 endoscopic routes converge, a so-called connection areas, are missing in the scientific literature.

OBJECTIVE

To identify all the skull base areas and anatomic structures where endonasal and transorbital endoscopic avenues could be connected and combined.

METHODS

Five cadaveric specimens (10 sides) were used for dissection. Qualitative description and quantitative analysis of each connection areas were performed.

RESULTS

At the anterior cranial fossa, the connection area was found at the level of the sphenoid planum; in the middle cranial fossa, it was at the Mullan triangle; finally, in the posterior cranial fossa, the connection area was just behind the medial portion of the petrous apex. The average extradural working areas through the transorbital approach were 4.93, 12.93, and 1.93 cm 2 and from the endonasal corridor were 7.75, 10.45, and 7.48 cm 2 at the level of anterior, middle, and posterior cranial fossae, respectively.

CONCLUSION

The combined endonasal and transorbital endoscopic approach is an innovative entity of skull base neurosurgery. From the anatomic point of view, our study demonstrated the feasibility of this combined approach to access the entire skull base, by both corridors, identifying a working connection area in each cranial fossa. These data could be extremely useful during the surgical planning to predict which portion of a lesion could be removed through each route and to optimize patients' care.

Superior eyelid endoscopic transorbital approach to the tentorial area: A qualitative and quantitative anatomic study

Objective

Superior eyelid endoscopic transorbital approach (SETOA) is nowadays gaining progressive application in neurosurgical scenarios. Both anatomic and clinical reports have demonstrated the possibility of taking advantage of the orbital corridor as a minimally invasive route to reach anterior and middle cranial fossae and manage selected surgical lesions developing in these areas. The aim of this paper is to further shed light on other anatomic regions of the skull base as seen from a transorbital perspective, namely, the posterior cranial fossa and tentorial area, describing technical feasibility and steps in reaching this area through an extradural-transtentorial approach and providing quantitative evaluations of the "working area" obtained through this route.

Material and methods

Four cadaveric heads (eight sides) were dissected at the Laboratory of Surgical Neuroanatomy (LSNA) of the University of Barcelona, Spain. A stepwise dissection of the transorbital approach to the tentorial area was described. Qualitative anatomical descriptions and quantitative analyses of working were evaluated by using pre- and postdissections CT and MRI scans, and three-dimensional reconstructions were made using Amira software.

Results

With the endoscopic transorbital approach, posterior cranial fossa dura was reached by an extradural middle cranial fossa approach and drilling of the petrous apex. After clipping the superior petrosal sinus, the tentorium was divided and cut. An endoscope was then introduced in the posterior cranial fossa at the level of the tentorial incisura. Qualitative analysis provided a description of the tentorial and petrosal surfaces of the cerebellum, middle tentorial incisura, cerebellopontine fissures, and, after arachnoid dissection, by a 30° endoscopic visualization, the posterior aspect of the cerebellomesencephalic fissure. Quantitative analysis of the "working area" obtained after bone removal was also provided.

Conclusions

This anatomic qualitative and quantitative study sheds light on the anatomy of the posterior cranial fossa contents, such as the tentorial area and incisura, as seen through a transorbital perspective. The first aim of the article is to enrich the anatomical knowledge as seen through this relatively new corridor and to provide quantitative details and insights into the technical feasibility of reaching these regions in a surgical scenario.