The Inferolateral Transorbital Endoscopic Approach: A Preclinical Anatomic Study

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.

Inferior orbital fissure release to access the inferolateral orbital apex

OBJECTIVE

To describe release of the inferior orbital fissure (IOF) as a novel surgical technique that will improve access to the inferior and inferolateral orbital apex.

DESIGN

Laboratory investigation.

PARTICIPANTS

Human cadaver heads.

METHODS

Cadaveric dissection study whereby the technique of an IOF release was performed. A swinging eyelid preseptal approach was used to enable a subperiosteal dissection to the orbital floor without obstruction from orbital fat prolapse. A plane was dissected between periorbita and Muller's muscle, the smooth muscle that overlies the entire length of the IOF. Measurements were taken in the sagittal plane from a point on the inferior orbital rim directly above the infraorbital foramen to the most posterior aspect of the orbital floor.

RESULTS

Fifteen orbits from 8 cadaver heads were dissected with the aid of a rigid 0-degree endoscope and microsurgical instruments. This study demonstrated that an additional 10.93 ± 2.10 mm of access to the orbital apex was gained after the release of periorbita from the IOF.

CONCLUSION

We propose that the IOF release can be adopted as an adjunctive technique to orbital surgery of the inferior and inferolateral orbital apex.

Quantitative Anatomical Comparison of Surgical Approaches to Meckel's Cave

BACKGROUND

Meckel's cave is a challenging surgical target due to its deep location and proximity to vital neurovascular structures. Surgeons have developed various microsurgical transcranial approaches (MTAs) to access it, but there is no consensus on the best method. Newer endoscopic approaches have also emerged. This study seeks to quantitatively compare these surgical approaches to Meckel's cave, offering insights into surgical volumes and exposure areas.

METHODS

Fifteen surgical approaches were performed bilaterally in six specimens, including the pterional approach (PTA), fronto-temporal-orbito-zygomatic approach (FTOZA), subtemporal approach (STA), Kawase approach (KWA), retrosigmoid approach (RSA), retrosigmoid approach with suprameatal extension (RSAS), endoscopic endonasal transpterygoid approach (EETPA), inferolateral transorbital approach (ILTEA) and superior eyelid approach (SEYA). All the MTAs were performed both with 10 mm and 15 mm of brain retraction, to consider different percentages of surface exposure. A dedicated navigation system was used to quantify the surgical working volumes and exposure of different areas of Meckel's cave (ApproachViewer, part of GTx-Eyes II, University Health Network, Toronto, Canada). Microsurgical transcranial approaches were quantified with two different degrees of brain retraction (10 mm and 15 mm). Statistical analysis was performed using a mixed linear model with bootstrap resampling.

RESULTS

The RSAS with 15 mm of retraction offered the maximum exposure of the trigeminal stem (TS). If compared to the KWA, the RSA exposed more of the TS (69% vs. 46%; p = 0.01). The EETPA and ILTEA exposed the Gasserian ganglion (GG) mainly in the anteromedial portion, but with a significant 20% gain in exposure provided by the EETPA compared to ILTEA (42% vs. 22%; p = 0.06). The STA with 15 mm of retraction offered the maximum exposure of the GG, with a significant gain in exposure compared to the STA with 10 mm of retraction (50% vs. 35%; p = 0.03). The medial part of the three trigeminal branches was mainly exposed by the EETPA, particularly for the ophthalmic (66%) and maxillary (83%) nerves. The EETPA offered the maximum exposure of the medial part of the mandibular nerve, with a significant gain in exposure compared to the ILTEA (42% vs. 11%; p = 0.01) and the SEY (42% vs. 2%; p = 0.01). The FTOZA offered the maximum exposure of the lateral part of the ophthalmic nerve, with a significant gain of 67% (p = 0.03) and 48% (p = 0.04) in exposure compared to the PTA and STA, respectively. The STA with 15 mm of retraction offered the maximum exposure of the lateral part of the maxillary nerve, with a significant gain in exposure compared to the STA with 10 mm of retraction (58% vs. 45%; p = 0.04). The STA with 15 mm of retraction provided a significant exposure gain of 23% for the lateral part of the mandibular nerve compared to FTOZA with 15 mm of retraction (p = 0.03).

CONCLUSIONS

The endoscopic approaches, through the endonasal and transorbital routes, can provide adequate exposure of Meckel's cave, especially for its more medial portions, bypassing the impediment of major neurovascular structures and significant brain retraction. As far as the most lateral portion of Meckel's cave, MTA approaches still seem to be the gold standard in obtaining optimal exposure and adequate surgical volumes.

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.

Transorbital transposition of the temporoparietal fascia flap to reconstruct the skull base defects: A preclinical study with comparison to the transpterygoid transposition

BACKGROUND

Transpterygoid transposition of the temporoparietal fascia flap (TPFF) is a feasible selection for ventral skull base defect (VSBD) reconstruction, but not anterior skull base defect (ASBD) reconstruction, after expanded endoscopic endonasal approach (EEEA). The goal of this study is to introduce the transorbital transposition of the TPFF for skull base defects reconstruction after EEEA, and make quantitative comparison between the transpterygoid transposition and transorbital transposition.

METHODS

Cadaveric dissections were performed in five adult cadaveric heads with creating three transporting corridors bilaterally, encompassing superior transorbital corridor, inferior transorbital corridor, and transpterygoid corridor. For each transporting corridor, the minimum necessary length of the TPFF for skull base defects reconstruction was measured.

RESULTS

The areas of ASBD and VSBD were 1019.63 ± 176.32 mm2 and 572.99 ± 126.21 mm2 . The length of the harvested TPFF was 149.38 ± 6.21 mm. In contrast to the transpterygoid transposition with incomplete coverage, transorbital transposition of the TPFF allowed full coverage of ASBD with a minimum necessary length of 109.75 ± 8.31 mm. For VSBD reconstruction, transorbital transposition of the TPFF needs shorter minimum necessary length (123.88 ± 4.49 mm) than transpterygoid transposition (138.00 ± 6.28 mm).

CONCLUSIONS

Transorbital corridor is a novel pathway for transporting the TPFF into the sinonasal cavity for skull base defects reconstruction after EEEA. In comparison with transpterygoid transposition, transorbital transposition provides wider coverage of skull base defects with a fixed length of the TPFF.

Transuncal Selective Amygdalohippocampectomy by an Inferolateral Preseptal Endoscopic Approach Through Inferior Eyelid Conjunctival Incision: An Anatomic Study

BACKGROUND

Transorbital endoscopic approaches have been described for pathologies of anterior and middle fossae. Standard lateral orbitotomy gives access to mesial temporal lobe, but the axis of work is partially obscured by the temporal pole and working corridor is limited.

OBJECTIVE

To evaluate the usefulness of an inferolateral orbitotomy to provide a more direct corridor to perform a transuncal selective amygdalohippocampectomy.

METHODS

Three adult cadaveric specimens were used for a total of 6 dissections. A step-by-step description and illustration of the transuncal corridor for a selective amygdalohippocampectomy were performed using the inferolateral orbitotomy through an inferior eyelid conjunctival incision. The anatomic landmarks were demonstrated in detail. Orbitotomies and angles of work were measured from computed tomography scans, and the area of resection was illustrated by postdissection MRI.

RESULTS

Inferior eyelid conjunctival incision was made for exposure of the inferior orbital rim. Inferolateral transorbital approach was performed to access the transuncal corridor. Endoscopic selective amygdalohippocampectomy was performed through the entorhinal cortex without damage to the temporal neocortex or Meyer's loop. The mean horizontal diameter of the osteotomy was 14.4 mm, and the vertical one was 13.6 mm. The mean angles of work were 65° and 35.5° in the axial and sagittal planes, respectively. Complete amygdalohippocampectomy was achieved in all 6 dissections.

CONCLUSION

Transuncal selective amygdalohippocampectomy was feasible in cadaveric specimens using the inferolateral transorbital endoscopic approach avoiding damage to the temporal neocortex and Meyer's loop. The inferior eyelid conjunctival incision may result in an excellent cosmetic outcome.

Endoscopic transorbital approach for skull base lesions: a report of 16 clinical cases

Due to the deep location, complex anatomy, and adjacent vital neurovascular structures, skull base surgery is challenging and requires specific approaches. The emerging endoscopic transorbital approach (eTOA) technique provides a new approach to the orbital content, spheno-orbital region, lateral cavernous sinus, and Meckel's cave. In this study, the clinical utility and effectiveness of the eTOA are reported. Sixteen cases who underwent the eTOA were included in the current study. The patients were divided into 3 groups according to tumor location: Group A (intraorbital, 6 cases), group B (spheno-orbital, 7 cases), and group C (cavernous sinus, and Meckel's cave, 3 cases). The clinical data and surgical results were analyzed. Eight meningiomas, 2 hemangiomas, 1 low-grade glioma, 1 instance of inflammatory hyperplasia tissue, 1 Langerhans cell histiocytosis, 1 epidermoid cyst, 1 trigeminal schwannoma, and 1 bone fibrosis hyperplasia were observed. The mean tumor diameter was 2.4 cm. A single case in Group A and Group C underwent biopsy (12.5%), and 1 case of fibrous dysplasia in Group B underwent sufficient orbit decompression (6.25%). The remaining 13 cases underwent gross total tumor resection (81.25%). No cerebral-spinal fluid leak or infection occurred. And no cosmetic problems or significant complications were observed during the follow-up. As a minimally invasive technique, the eTOA has unique advantages for carefully selected skull base lesions because of its direct route, short working distance, and distinct attack angle.

Endoscopic Transorbital Approach to the Middle Fossa: Qualitative and Quantitative Anatomic Study

BACKGROUND

The endoscopic superior eyelid transorbital route to the skull base is gaining progressive popularity in the neurosurgical community.

OBJECTIVE

To evaluate the anatomy of the middle cranial fossa from this novel ventral perspective to reach the skull base through the transorbital route and to show limits for possible safe middle fossa drilling from the transorbital route.

METHODS

Anatomic study was performed; 5 cadaveric specimens (ie, 10 sides) and 2 dry skulls (ie, 4 sides) were dissected.

RESULTS

To obtain a functional result, there are boundaries that correspond to neurovascular structures that traverse, enter, or leave the middle fossa that must be respected: inferiorly, the lateral pterygoid muscle; medially, the Gasserian ganglion and the lateral border of the foramen rotundum; laterally, the foramen spinosum with the middle meningeal artery; superiorly, the lesser sphenoid wing; posteriorly, the anterior border of the foramen ovale. Average bone resected was 6.49 ± 0.80 cm3 which is the 63% of total middle fossa floor. The mean axial surgical length calculated was 3.85 cm (3.18-5.19 cm) while the mean sagittal surgical length was 5.23 cm (4.87-6.55 cm). The mean horizontal angle of approach was 38.14° (32.87°-45.63°), while the mean vertical angle of approach was 18.56° (10.81°-26.76°).

CONCLUSION

Detailed anatomy of the middle cranial fossa is presented, and herewith we demonstrated that from the endoscopic superior eyelid transorbital approach removal of middle cranial fossa floor is possible when anatomic landmarks are respected.

Combined endoscopic endonasal and transorbital multiportal approach for complex skull base lesions involving multiple compartments

PURPOSE

This study defines the specific areas that connect the surgical corridors of the endoscopic endonasal (EEA) and transorbital approach (TOA) to identify adequate clinical applications and perspectives of this combined multiportal approach.

METHODS

Consecutive patients who underwent combined EEA and TOA procedures for various pathologies involving multiple compartments of the skull base were enrolled.

RESULTS

A total of eight patients (2 chondrosarcomas, 2 meningiomas, 2 schwannomas, 1 glioma, and 1 traumatic optic neuropathy) were included between August 2016 and April 2021. The cavernous sinus (CS) was targeted as the connection area of the combined approach in four patients with tumors infiltrating the middle cranial fossa (MCF) and central skull base through the CS. For two patients with MCF tumors extending into the infratemporal fossa (ITF), the horizontal portion of the greater sphenoid wing and the foramen ovale were utilized as the connection area. In the remaining 2 patients, connection was achieved through the optic canal (OC). Gross total and near total resection was achieved in 5 patients with tumors, and circumferential removal of bone composing the OC was performed in one patient with traumatic compressive optic neuropathy. Postoperative complications included one cardiac arrest due to underlying cardiovascular disease and one case of oculomotor nerve palsy.

CONCLUSIONS

The combined EEA and TOA procedure is a useful strategy for complex lesions involving multiple compartments of the skull base. Herein, we identified the specific areas connecting the two surgical approaches, allowing a common path for EEA and TOA procedures.

Eyebrow incision with a crescent-shaped orbital rim craniotomy for microscopic and endoscopic transorbital approach to the anterior and middle cranial fossa: A cadaveric study and case presentation

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The transorbital approach combining eyebrow incision and crescent-shaped craniotomy increases the surgical freedom to access the anterior and middle skull-base.

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The technic allows the use of both endoscope and microscope.

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The concept is at the crossroad between the supraorbital keyhole and endoscopic trans-orbital approach.

Resection of the internal carotid artery in selected patients affected by cancer of the skull base

Invasion of the internal carotid artery (ICA) has been historically considered a criterion of non-resectability of skull base cancer (SBC). Patients affected by SBC who underwent surgery including resection of ICA at two tertiary institutions were included. Demographics, oncologic, and surgical information, complications, and survival outcomes were retrospectively reviewed. Survival outcomes were calculated. Ten patients were included. Three surgical approaches (transnasal endoscopic, transorbital, and transpetrosal) were employed to resect the invaded/abutted tract(s) of the ICA. All patients underwent ICA temporary balloon occlusion test. In two patients, an extracranial-to-intracranial arterial bypass was harvested. Major neuromorbidity was observed in two patients. Perioperative mortality of the series was 10.0%. Mean overall survival was 27.2 months, with 2-year overall and progression-free survival rate of 88.9%. ICA resection is feasible as part of the ablation performed for very advanced SBCs. Survival outcomes are acceptable in adequately selected patients.

Endoscopic Transorbital Approach to Mesial Temporal Lobe for Intra-Axial Lesions: Cadaveric Study and Case Series (SevEN-008)

BACKGROUND

Endoscopic transorbital approach (ETOA) has been proposed as a minimally invasive technique for the treatment of skull base lesions located around mesial temporal lobe (MTL), mostly extra-axial pathology.

OBJECTIVE

To explore the feasibility of ETOA in accessing intraparenchymal MTL with cadaveric specimens and describe our initial clinical experience of ETOA for intra-axial lesions in MTL.

METHODS

Anatomic dissections were performed in 4 adult cadaveric heads using a 0° endoscope. First, a stepwise anatomical investigation of ETOA to intraparenchymal MTL was explored. Then, ETOA was applied clinically for 7 patients with intra-axial lesions in MTL, predominantly high-grade gliomas (HGGs) and low-grade gliomas (LGGs).

RESULTS

The extradural stage of ETOA entailed a superior eyelid incision followed by orbital retraction, drilling of orbital roof, greater and lesser wing of sphenoid bone, and cutting of the meningo-orbital band. For the intradural stage, the brain tissue medial to the occipito-temporal gyrus was aspirated until the temporal horn was opened. The structures of MTL could be aspirated selectively in a subpial manner without injury to the neurovascular structures of the ambient and sylvian cisterns, and the lateral neocortex. After cadaveric validation, ETOA was successfully performed for 4 patients with HGGs and 3 patients with LGGs. Gross total resection was achieved in 6 patients (85.7%) without significant surgical morbidities including visual field deficits.

CONCLUSION

ETOA provides a logical line of access for intra-axial lesions in MTL. The safe and natural surgical trajectory of ETOA can spare brain retraction, neurovascular injury, and disruption of the lateral neocortex.

Quantitative Anatomic Comparison of Microsurgical Transcranial, Endoscopic Endonasal, and Transorbital Approaches to the Spheno-Orbital Region

BACKGROUND

The spheno-orbital region (SOR) is a complex anatomic area that can be accessed with different surgical approaches.

OBJECTIVE

To quantitatively compare, in a preclinical setting, microsurgical transcranial approaches (MTAs), endoscopic endonasal transpterygoid approach (EEA), and endoscopic transorbital approaches (ETOAs) to the SOR.

METHODS

These approaches were performed in 5 specimens: EEA, ETOAs (superior eyelid and inferolateral), anterolateral MTAs (supraorbital, minipterional, pterional, pterional-transzygomatic, and frontotemporal-orbitozygomatic), and lateral MTAs (subtemporal and subtemporal transzygomatic). All specimens underwent high-resolution computed tomography; an optic neuronavigation system with dedicated software was used to quantify working volume and exposed area for each approach. Mixed linear models with random intercepts were used for statistical analyses.

RESULTS

Anterolateral MTAs offer a direct route to the greater wings (GWs) and lesser wings (LWs); only they guarantee exposure of the anterior clinoid. Lateral MTAs provide access to a large area corresponding to the GW, up to the superior orbital fissure (SOF) anteriorly and the foramen rotundum medially. ETOAs also access the GW, close to the lateral portion of SOF, but with a different angle of view as compared to lateral MTAs. Access to deep and medial structures, such as the lamina papyracea and the medial SOF, is offered only by EEA, which exposes the LW and GW only to a limited extent.

CONCLUSION

This is the first study that offers a quantitative comparison of the most used approaches to SOR. A detailed knowledge of their advantages and limitations is paramount to choose the ideal one, or their combination, in the clinical setting.

Endoscopic endonasal and transorbital approaches to petrous apex lesions

OBJECTIVE

The petrous apex (PA) is one of the most challenging areas in skull base surgery because it is surrounded by numerous critical neurovascular structures. The authors analyzed the clinical outcomes of patients who underwent endoscopic endonasal approach (EEA) and transorbital approach (TOA) procedures for lesions involving PA to determine the perspectives and proper applications of these two approaches.

METHODS

The authors included patients younger than 80 years with lesions involving PA who were treated between May 2015 and December 2019 and had regular follow-up MR images available for analysis. Patients with meningioma involving petroclival regions were excluded. The authors classified PA into three regions: superior to the petrous segment of the internal carotid artery (p-ICA) (zone 1); posterior to p-ICA (zone 2); and inferior to p-ICA (zone 3). Demographic data, preoperative clinical and radiological findings, surgical outcomes, and morbidities were reviewed.

RESULTS

A total of 19 patients with lesions involving PA were included. Ten patients had malignant tumor (chondrosarcoma, chordoma, and osteosarcoma), and 6 had benign tumor (schwannoma, Cushing's disease, teratoma, etc.). Three patients had PA cephalocele (PAC). Thirteen patients underwent EEA, and 5 underwent TOA. Simultaneous combined EEA and TOA was performed on 1 patient. Thirteen of 16 patients (81.3%) had gross- or near-total resection. Tumors within PA were completely resected from 13 of 16 patients using a view limited to only the PA. Complete obliteration of PAC was achieved in all patients. Postoperative complications included 2 cases of CSF leak, 1 case of injury to ICA, 1 fatality due to sudden herniation of the brainstem, and 1 case of postoperative diplopia.

CONCLUSIONS

EEA is a versatile surgical approach for lesions involving all three zones of PA. Clival tumor spreading to PA in a medial-to-lateral direction is a good indication for EEA. TOA provided a direct surgical corridor to the superior portion of PA (zone 1). Patients with disease with cystic nature are good candidates for TOA. TOA may be a reasonable alternative surgical treatment for select pathologies involving PA.

Inferolateral Transorbital Endoscopic Approach for Spheno-Orbital Meningiomas

ABSTRACT

Spheno-orbital meningiomas (SOM) are slow growing tumors that often cause proptosis and visual deficits, due to direct compression of adjacent structures or hyperostosis of surrounding bones.Traditionally, these lesions are approached via a lateral transcranial route. Recent interest in mini-invasive surgery and endoscopy brought many authors to study different trans-nasal or trans-orbital approaches.The authors report a surgical case series with 3 patients with proptosis due to SOM who underwent surgery in our institution via an inferolateral trans-orbital endoscopic approach. The authors described our surgical technique and the authorsretrospectively reviewed the clinical and radiological outcomes of the patients.All 3 patients had an effective orbital decompression with improvement of the proptosis and pain relief. Histological examination was possible and no intraoperative nor postoperative complications were observed.Therefore, the authors consider inferolateral trans-orbital endoscopic approach as a feasible approach for lesions involving the lateral orbit compartment arising from middle cranial fossa or from orbit itself.

Endoscopic Subtemporal Epidural Key-Hole Approach: Quantitative Anatomic Analysis of Three Surgical Corridors

BACKGROUND

The endoscope-assisted subtemporal key-hole epidural approach (ESKEA) has been recently described. The aim of this study was to measure working volumes and exposure of key areas of the middle cranial fossa provided by this approach.

METHODS

Four fresh frozen cadaver heads were dissected to analyze 3 modular corridors (1A, 1B, and 2) harvested through ESKEA. A step-by-step dissection was performed, and key anatomic landmarks were recorded. A GTxEyesII-ApproachViewer was used to quantify the working volume and exposure of 4 different regions (sphenoorbital, parasellar, superior petrous apex, and squamopetrous). For each corridor, 3 incremental degrees of temporal dural retraction (5, 10, and 15 mm) were tested.

RESULTS

The working volume of all corridors progressively increased with degree of retraction: Corridors 1A, 1B, and 2 showed a gain in working volume of 21%, 27%, and 19% from 5 mm to 10 mm retraction, respectively, and a gain of 40%, 45%, and 44% from 5 mm to 15 mm retraction, respectively. The sphenoorbital area was exposed (27%-45%) through corridor 1A, and exposure significantly increased with the degree of retraction. Corridor 1B provided optimal exposure of parasellar areas (86%-100%) and superior petrous apex (70%-87%) regardless of the degree of retraction. The squamopetrous area was satisfactorily addressed through corridor 2 (88%) only with the highest degree of retraction.

CONCLUSIONS

ESKEA can be conceived as a modular approach: the 3 surgical corridors have specific working volumes, which are clearly influenced by the degree of temporal lobe retraction, and provide exposure of different middle cranial fossa areas.

Transorbital Neuroendoscopic Surgery as a Mainstream Neurosurgical Corridor: A Systematic Review

BACKGROUND

Transorbital neuroendoscopic surgery (TONES) offers a new level of minimally invasive, minimally disfiguring skull base surgery with maximal surgical visualization.

METHODS

This review systematically assesses the body of published anatomic (cadaveric) and clinical evidence for the approach. PubMed, Cochrane Library, Ovid MEDLINE, and Embase were systematically searched for articles in which the TONES surgical technique was used in an anatomic, clinical, or combined study. The outcomes of interest included identification of the diseases, operative outcomes, and complication rates.

RESULTS

Twenty-three articles were selected for this systematic review: 10 were purely anatomic, 10 were clinical, and 3 had both clinical and cadaveric components. The articles reported 69 patients undergoing transorbital or combined transorbital and transnasal intervention. A total of 30 cases of cerebrospinal fluid leak were documented; of these, 28 (93%) had successful resolution, 2 (7%) had recurrence, and 5 (15%) experienced complications. A total of 31 tumors were biopsied (n = 1), resected (n = 22), or debulked (n = 8). Meningiomas were the most common lesion managed via TONES, with 5 of 7 patients with meningioma who reported preoperative neurologic deficits experiencing an improvement in extraocular movement impairment, visual acuity, proptosis, and ptosis. Transient postoperative clinical sequelae, including diplopia and ptosis, were increasingly associated with the superior lid crease incision and the sole transorbital approach.

CONCLUSIONS

TONES is a significant development in transorbital skull base surgery. However, comprehensive, robust, comparative analyses and increasing use and generalizability of this technique in skull base surgery are awaited.

Endoscopic transorbital ligation of the maxillary artery through the inferior orbital fissure

OBJECTIVE

Determine the feasibility of accessing the internal maxillary artery (IMA) through a transorbital endoscopic assisted approach through the inferior orbital fissure (IOF).

MATERIALS AND METHODS

Six adult cadaveric specimens were injected intravascularly with colored latex and dissected on 12 sides. A transorbital endoscopic approach was used to expose the IOF and reach the IMA.

RESULTS

The average length and width of the anterolateral segment of the IOF were 7.3 and 4 mm, respectively, on the right side and 6.7 and 3.8 mm, respectively, on the left side. Surgical exposure and modification of the IOF allowed the exposure and control of the IMA in all 12 sides.

CONCLUSIONS

The IOF is a feasible portal to the IMA. The benefits of this approach include vascular control of the distal segment of the maxillary artery. It may provide access in clinical scenarios where endonasal access is not possible (e.g., extensive tumors) or serve as an alternative or complementary surgical route (e.g., control during a total or radical maxillectomy).

Endoscopic Transorbital Approaches to Anterior and Middle Cranial Fossa: Exploring the Potentialities of a Modified Lateral Retrocanthal Approach

BACKGROUND

Among the new perspectives to revolutionize skull base surgery, there are the transorbital neuroendoscopic (TONES) approaches to reach the anterior and middle cranial fossa (ACF and MCF). We conceived to explore the potentialities of a modified superiorly and medially extended lateral retrocanthal (LRC) approach.

METHODS

Six head specimens were dissected. Applying the established conic model and the key surgical landmark of sphenofrontal suture, we tested the feasibility of a modified LRC to reach ACF and MCF; computed tomography (CT) scans were performed before and after dissection to obtain a morphometric analysis of the surgical corridors using a polygonal surfaces model.

RESULTS

Through our anatomical study, we were able to identify and explore 3 different surgical corridors to reach the ACF and MCF: the superomedial, the superolateral, and the inferolateral. The superomedial corridor appeared most suitable to reach the medial part of the ACF and the optic-carotid region, whereas through the superolateral and inferolateral corridors it was possible to reach and explore the lateral part of ACF and MCF. The mean volumes of the 3 surgical corridors calculated on post-dissection CT scans were: 12.72 ± 1.99, 5.69 ± 0.34, and 6.24 ± 0.47 cm³, respectively.

CONCLUSIONS

The development of TONES approaches has not replaced the traditional open or endoscopic approach; nonetheless, identification of surgical corridors and the possibility to combine them represent a major breakthrough. Clinical studies are necessary to demonstrate their validity and test the effectiveness, safety, and reproducibility of TONES approaches in managing lesions harboring in the ACF and MCF.

Access to Meckel's cave for biopsies of indeterminate lesions: a systematic review

Accessing Meckel's cave (MC) is surgically challenging. Open approaches are complex and often correlated with high morbidity. Endoscopic approaches emerged in the last decade as feasible alternatives to open approaches, especially for sampling indeterminate lesions. This article first analyses available routes to approach Meckel's cave and presents furthermore an illustrative case. We conducted a systematic review and reported according to the guidelines for preferred reporting items for systematic reviews and meta-analyses (PRISMA). Various surgical approaches identified through the search are evaluated and discussed in detail. Additionally, we report on a case of woman with a lesion in MC, which was accessed through an endoscopic transpterygoid approach subsequently diagnosed as a diffuse large B cell lymphoma. Our search delivered 75 articles that included case reports (n = 21), cadaveric studies (n = 32), clinical articles (n = 16), review of the literatures (n = 3), as well as technical notes (n = 2) and a radiological manuscript (n = 1). Open routes included lateral approaches with many variations, mainly intra- and extradural pterional approaches and anterior petrosal, as well as a retrosigmoid intradural suprameatal and a lateral transorbital approach. Endoscopically, MC was reached via approaches that included transpterygoid, transorbital or infraorbital fissure routes. Percutaneous approaches, e.g. through the foramen ovale, were also described. Multiple surgical approaches to MC are currently available. Their different characteristics as well as individual patient factors, such as clinical history and the localization of the disease, have to be considered when choosing a surgical corridor. Studies included in this review highlight the endonasal endoscopic transpterygoidal technique as an excellent corridor for biopsies in the ventral MC.

Transorbital endoscopic approaches to the skull base: a systematic literature review and anatomical description

Transorbital endoscopic approaches are increasing in popularity as they provide corridors to reach various areas of the ventral skull base through the orbit. They can be used either alone or in combination with different approaches when dealing with the pathologies of the skull base. The objective of the current study is to evaluate the surgical anatomy of transorbital endoscopic approaches by cadaver dissections as well as providing objective clinical data on their actual employment and morbidity through a systematic review of the current literature. Four cadaveric specimens were dissected, and step-by-step dissection of each endoscopic transorbital approach was performed to identify the main anatomic landmarks and corridors. A systematic review with pooled analysis of the current literature from January 2000 to April 2020 was performed and the related studies were analyzed. Main anatomical landmarks are presented based on the anatomical study and systematic review of the literature. With emphasis on the specific transorbital approach used, indications, surgical technique, and complications are reviewed through the systematic review of 42 studies (19 in vivo and 23 anatomical dissections) including 193 patients. In conclusion, transorbital endoscopic approaches are promising and appear as feasible techniques for the surgical treatment of skull base lesions. Surgical anatomy of transorbital endoscopic approaches can be mastered through knowledge of a number of anatomical landmarks. Based on data available in the literature, transorbital endoscopic approaches represent an important complementary that should be included in the armamentarium of a skull base team.

Endoscopic transorbital approach to the infratemporal fossa and parapharyngeal space: a cadaveric study

OBJECTIVE

The infratemporal fossa (ITF) and parapharyngeal space are anatomical regions that can be challenging to access without the use of complex, cosmetically disfiguring approaches. With advances in endoscopic techniques, a new group of surgical approaches to access the intracranial space through the orbit has been recently referred to as transorbital neuroendoscopic surgery (TONES). The objective of this study was to establish a transorbital endoscopic approach utilizing the inferior orbital fissure (IOF) to gain access to the ITF and parapharyngeal space and provide a detailed endoscopic anatomical description of this approach.

METHODS

Four cadaveric heads (8 sides) were dissected using a TONES approach through the IOF to reach the ITF and parapharyngeal space, providing stepwise dissection with detailed anatomical findings and a description of each step.

RESULTS

An inferior eyelid approach was made with subperiosteal periorbital dissection to the IOF. The zygomatic and greater wing of the sphenoid were drilled, forming the boundaries of the IOF. The upper head of the lateral pterygoid muscle in the ITF and parapharyngeal space was removed, and 7 distinct planes were described, each with its own anatomical contents. The second part of the maxillary artery was mainly found in plane 1 between the temporalis laterally and the lateral pterygoid muscle in plane 2. The branches of the mandibular nerve (V3) and middle meningeal artery (MMA) were identified in plane 3. Plane 4 was formed by the fascia of the medial pterygoid muscle (MTM) and the tensor veli palatini muscle. The prestyloid segment, found in plane 5, was composed mainly of fat and lymph nodes. The parapharyngeal carotid artery in the poststyloid segment, found in plane 7, was identified after laterally dissecting the styloid diaphragm, found in plane 6. V3 and the origin of the levator and tensor veli palatini muscles serve as landmarks for identification of the parapharyngeal carotid artery.

CONCLUSIONS

The transorbital endoscopic approach provides excellent access to the ITF and parapharyngeal space compared to previously described complex and morbid transfacial or transcranial approaches. Using the IOF is an important and useful landmark that permits a wide exposure.

Morphometric and Volumetric Measurements of Orbit With Cone-Beam Computed Tomography

PURPOSE

The purpose of this study was to determine cone-beam computed tomography (CBCT) as a tool for measuring morphometric and volumetric measurements of the orbit. Also, to assess gender and age variations and compare traditional methods of measurements in dry-skull, cadaveric, and other imaging modalities.

PATIENTS AND METHODS

Morphometric and volumetric values of 98 orbits (49 subjects, 21 men/28 women) were measured using CBCT. Their mean and standard deviation were measured and analyzed. The gender and age variability older and younger than 40 years were evaluated. They were compared with other dry-skull and imaging studies done among different populations.

RESULTS

CBCT could accurately measure the various morphometric and volumetric parameters of the orbit. From the reference point infraorbital foramen (I) to lacrimal fossa (F1), inferior orbital fissure (F2), inferior orbital rim (F3), and the optic canal (F4) were (in mm) (mean ± SD) 22.88 ± 1.08, 32.53 ± 0.88, 7.44 ± 0.71, and 51.45 ± 1.28, respectively. From the reference point, superior orbital notch/foramen (S) to superior orbital fissure (S1), lacrimal fossa (S2), and the optic canal (S3) were 49.29 ± 2.1, 26.39 ± 1.58, and 46.82 ± 0.88, respectively. From the reference point frontozygomatic suture (L) to lacrimal fossa (L1), superior orbital fissure (L2), the optic canal (L3), and inferior orbital fissure (L4) were 18.19 ± 0.88, 39.91 ± 1.44, 47.63 ± 1.11, and 35.19 ± 1.02, respectively. Orbital volume was found to show a significant difference between older and younger than 40 years of age, though not significant compared between men and women.

CONCLUSION

CBCT is a viable tool for morphometric and volumetric measurements of the orbit and other orocraniofacial structures. It can also assess age and gender variability. The low cost, high accuracy, low radiation, and ease of use can help in reproducibility among the different living populations.

Quantitative comparison of endoscopically assisted endonasal, sublabial and transorbital transmaxillary approaches to the anterolateral skull base

OBJECTIVES

The aim of this anatomical study is to make quantitative comparison among three endoscopic approaches, encompassing contralateral endonasal transseptal transmaxillary transpterygoid approach (contralateral EEA), endoscopic sublabial transmaxillary transalisphenoid (Caldwell-Luc) approach and endoscopic transorbital transmaxillary approach through inferior orbital fissure (ETOA), to the anterolateral skull base for assisting preoperative planning.

DESIGN & PARTICIPANTS

Anatomical dissections were performed in four adult cadaveric heads bilaterally using three endoscopic transmaxillary approaches described above.

SETTING

Skull Base Laboratory at the National Defense Medical Center.

MAIN OUTCOME MEASURES

The area of exposure, angles of attack and depth of surgical corridor of each approach were measured and obtained for statistical comparison.

RESULTS

The ETOA had significantly larger exposure over middle cranial fossa (731.40 ± 80.08 mm² ) than contralateral EEA (266.60 ± 46.74 mm² ) and Caldwell-Luc approach (468.40 ± 59.67 mm² ). In comparison with contralateral EEA and Caldwell-Luc approach, the ETOA offered significantly greater angles of attack and shorter depth of surgical corridor (P < .05 for all comparisons).

CONCLUSIONS

The ETOA is the superior choice for target lesion occupying multiple compartments with its epicentre located in the middle cranial fossa or superior portion of infratemporal fossa.

Minimally Invasive Approaches to the Lateral Cavernous Sinus and Meckel's Cave: Comparison of Transorbital and Subtemporal Endoscopic Techniques

BACKGROUND

Transorbital and subtemporal keyhole approaches have recently been proposed to approach lesions in the lateral wall of the cavernous sinus (CS) and Meckel's cave (MC). Our goal was to compare these approaches and suggest indications for each of them.

METHODS

Five cadaver heads (10 sides, 40 procedures) were used. The lateral transorbital approaches were carried out without and with the removal of the lateral orbital rim, herein referred to as the lateral transorbital approach (LTOA) and the lateral orbital wall approach (LOWA). The subtemporal approaches were performed without and with the removal of the zygomatic arch, referred to as the subtemporal approach (STA) and the subtemporozygomatic approach (STZA). Five targets were chosen and 2 triangles were created representing the lateral wall of the CS and MC. Stereotactic measurements were quantified to calculate angles of attack, surgical freedom, and temporal lobe retraction for each approach.

RESULTS

LTOA presented the smaller horizontal angles of attack. LOWA increased the angles to the same level of STA and STZA. STA and STZA presented larger vertical angles of attack. The surgical freedom presented gradual increase from LTOA to LOWA, STA, and STZA. STA and STZA needed greater temporal lobe retraction for most targets.

CONCLUSIONS

LTOA is a good option to biopsy a lesion in the lateral wall of the CS and LOWA increased the surgical corridor to work with microsurgical techniques. STA and STZA could be better options when wide exposure is necessary, but temporal lobe retraction should be taken into consideration.

Quantitative anatomical comparison of transnasal and transcranial approaches to the clivus

BACKGROUND AND OBJECTIVE

The clivus was defined as "no man's land" in the early 1990s, but since then, multiple approaches have been described to access it. This study is aimed at quantitatively comparing endoscopic transnasal and microsurgical transcranial approaches to the clivus in a preclinical setting, using a recently developed research method.

METHODS

Multiple approaches were performed in 5 head and neck specimens that underwent high-resolution computed tomography (CT): endoscopic transnasal (transclival, with hypophysiopexy and with far-medial extension), microsurgical anterolateral (supraorbital, mini-pterional, pterional, pterional transzygomatic, fronto-temporal-orbito-zygomatic), lateral (subtemporal and subtemporal transzygomatic), and posterolateral (retrosigmoid, far-lateral, retrolabyrinthine, translabyrinthine, and transcochlear). An optic neuronavigation system and dedicated software were used to quantify the working volume of each approach and calculate the exposure of different clival regions. Mixed linear models with random intersections were used for statistical analyses.

RESULTS

Endoscopic transnasal approaches showed higher working volume and larger exposure compared with microsurgical transcranial approaches. Increased exposure of the upper clivus was achieved by the transnasal endoscopic transclival approach with intradural hypophysiopexy. Anterolateral microsurgical transcranial approaches provided a direct route to the anterior surface of the posterior clinoid process. The transnasal endoscopic approach with far-medial extension ensured a statistically larger exposure of jugular tubercles as compared with other approaches. Presigmoid approaches provided a relatively limited exposure of the ipsilateral clivus, which increased in proportion to their invasiveness.

CONCLUSIONS

This is the first anatomical study that quantitatively compares in a holistic way exposure and working volumes offered by the most used modern approaches to the clivus.

Quantitative Anatomical Comparison of Anterior, Anterolateral and Lateral, Microsurgical and Endoscopic Approaches to the Middle Cranial Fossa

OBJECTIVE

To quantitatively compare different microsurgical and endoscopic approaches to the middle cranial fossa in a preclinical setting with a novel, computer-based research method.

METHODS

Different approaches were performed bilaterally in 5 head and neck specimens that underwent high-resolution computed tomography scans: 5 transcranial anterolateral (supraorbital, mini-pterional, pterional, pterional-transzygomatic, fronto-temporal-orbito-zygomatic) without and with anterior clinoidectomy; 2 transcranial lateral (subtemporal and subtemporal-transzygomatic); 2 endoscopic transnasal (transpterygoid, transpterygoid to infratemporal fossa); 2 endoscopic transorbital (superior eyelid and inferolateral), and endoscopic transmaxillary. A dedicated navigation system was used to quantify surgical working volumes and exposure of different areas of the middle cranial fossa (ApproachViewer, part of GTx-Eyes II, University Health Network, Toronto, Canada). Statistical analysis was performed using a mixed linear model with bootstrap resampling.

RESULTS

Endoscopic transnasal and fronto-temporal-orbito-zygomatic approaches with anterior clinoidectomy showed the largest surgical volumes. Endoscopic approaches allowed a wider exposure of medial anatomical surfaces (e.g., the petrous apex) compared with transcranial ones. Transcranial approaches with larger craniotomies allowed the widest exposure of superomedial anatomical structures (e.g., roof of cavernous sinus). The resection of the zygomatic arch allowed exposure of more medial surfaces with an inferior to superior trajectory.

CONCLUSIONS

This study implemented a novel neuronavigation-based research method to quantitatively compare different approaches to the middle cranial fossa; its results might guide, after consideration of clinical implications, the choice of the neurosurgical approach to different areas of this complex skull base region.

Endoscopic transorbital surgery for Meckel's cave and middle cranial fossa tumors: surgical technique and early results

OBJECTIVE

Tumors involving Meckel's cave remain extremely challenging because of the surrounding complex neurovascular structures and deep-seated location. The authors investigated a new minimal-access technique using the endoscopic transorbital approach (eTOA) through the superior eyelid crease to Meckel's cave and middle cranial fossa lesions and reviewed the most useful surgical procedures and pitfalls of this approach.

METHODS

Between September 2016 and January 2018, the authors performed eTOA in 9 patients with tumors involving Meckel's cave and the middle cranial fossa. The lesions included trigeminal schwannoma in 4 patients, meningioma in 2 patients, metastatic brain tumor in 1 patient, chondrosarcoma in 1 patient, and dermoid cyst in 1 patient. In 7 of the 9 patients, eTOA alone was performed, while the other 2 patients underwent a combined eTOA and endoscopic endonasal approach or retrosigmoid craniotomy. Data including details of surgical techniques and clinical outcomes were recorded.

RESULTS

Gross-total resection was performed in 7 of the 9 patients (77.8%). Four patients underwent extended eTOA (with lateral orbital rim osteotomy). Drilling of the trapezoid sphenoid floor, a middle fossa "peeling" technique, and full visualization of Meckel's cave were applied to approach the lesions. Tumors were exposed and removed extradurally in 3 patients and intradurally in 6 patients. There was no postoperative CSF leak.

CONCLUSIONS

The eTOA affords a direct route to access Meckel's cave and middle cranial fossa lesions. With experience, this novel approach can be successfully applied to selected skull base lesions. To achieve successful removal of the tumor, emphasis should be placed on the importance of adequately removing the greater sphenoid wing and vertical crest. However, because of limited working space eTOA may not be an ideal approach for posterior fossa lesions.

Endoscopic transorbital approach to anterolateral skull base through inferior orbital fissure: a cadaveric study

BACKGROUND

Endoscopic transorbital approach (eTOA) has been announced as an alternative minimally invasive surgery to skull base. Owing to the inferior orbital fissure (IOF) connecting the orbit with surrounding pterygopalatine fossa (PPF), infratemporal fossa (ITF), and temporal fossa, the idea of eTOA to anterolateral skull base through IOF is postulated. The aim of this study is to access its practical feasibility.

METHODS

Anatomical dissections were performed in five human cadaveric heads (10 sides) using 0-degree and 30-degree endoscopes. A stepwise description of eTOA to anterolateral skull base through IOF was documented. The anterosuperior corner of the maxillary sinus in the horizontal plane of the upper edge of zygomatic arch was defined as reference point (RP). The distances between the RP to the foramen rotundum (FR), foramen ovale (FO), and Gasserian ganglion (GG) were measured. The exposed area of anterolateral skull base in the coronal plane of the posterior wall of the maxillary sinus was quantified.

RESULTS

The surgical procedure consisted of six steps: (1) lateral canthotomy with cantholysis and preseptal lower eyelid approach with periorbita dissection; (2) drilling of the ocular surface of greater sphenoid wing and lateral orbital rim osteotomy; (3) entry into the maxillary sinus and exposure of PPF and ITF; (4) mobilization of infraorbital nerve with drilling of the infratemporal surface of the greater sphenoid wing and pterygoid process; (5) exposure of middle cranial fossa, Meckel's cave, and lateral wall of cavernous sinus; and (6) reconstruction of orbital floor and lateral orbital rim. The distances measured were as follows: RP-FR = 45.0 ± 1.9 mm, RP-FO = 55.7 ± 0.5 mm, and RP-GG = 61.0 ± 1.6 mm. In comparison with the horizontal portion of greater sphenoid wing, the superior and inferior axes of the exposed area were 22.3 ± 2.1 mm and 20.5 ± 1.8 mm, respectively. With reference to the FR, the medial and lateral axes of the exposed area were 11.6 ± 1.1 mm and 15.8 ± 1.6 mm, respectively.

CONCLUSIONS

The eTOA through IOF can be used as a minimally invasive surgery to access whole anterolateral skull base. It provides a possible resolution to target lesion involving multiple compartments of anterolateral skull base.

Clinical and ophthalmological outcome of endoscopic transorbital surgery for cranioorbital tumors

OBJECTIVE

Cranioorbital tumors are complex lesions that involve the deep orbit, floor of the frontal bone, and lesser and greater wing of the sphenoid bone. The purpose of this study was to describe the clinical and ophthalmological outcomes with an endoscopic transorbital approach (TOA) in the management of cranioorbital tumors involving the deep orbit and intracranial compartment.

METHODS

The authors performed endoscopic TOAs via the superior eyelid crease incision in 18 patients (16 TOA alone and 2 TOA combined with a simultaneous endonasal endoscopic resection) with cranioorbital tumors from September 2016 to November 2017. There were 12 patients with sphenoorbital meningiomas. Other lesions included osteosarcoma, plasmacytoma, sebaceous gland carcinoma, intraconal schwannoma, cystic teratoma, and fibrous dysplasia. Ten patients had primary lesions and 8 patients had recurrent tumors. Thirteen patients had intradural lesions, while 5 had only extradural lesions.

RESULTS

Of 18 patients, 7 patients underwent gross-total resection of the tumor and 7 patients underwent planned near-total resection of the tumor, leaving the cavernous sinus lesion. Subtotal resection was performed in 4 patients with recurrent tumors. There was no postoperative CSF leak requiring reconstruction surgery. Fourteen of 18 patients (77.8%) had preoperative proptosis on the ipsilateral side, and all 14 patients had improvement in exophthalmos; the mean proptosis reduced from 5.7 ± 2.7 mm to 1.5 ± 1.4 mm. However, some residual proptosis was evident in 9 of the 14 (64%). Ten of 18 patients (55.6%) had preoperative optic neuropathy, and 6 of them (60.0%) had improvement; the median best-corrected visual acuity improved from 20/100 to 20/40. Thirteen of 18 patients showed mild ptosis at an immediate postoperative examination, all of whom had a spontaneous and complete recovery of their ptosis during the follow-up period. Three of 7 patients showed improvement in extraocular motility after surgery.

CONCLUSIONS

Endoscopic TOA can be considered as an option in the management of cranioorbital tumors involving complex anatomical areas, with acceptable sequelae and morbidity.

Endoscopic transorbital transtentorial approach to middle incisural space: preclinical cadaveric study

BACKGROUND

Endoscopic transorbital approach is a novel development of minimally invasive skull base surgery. Recently, anatomical studies have started to discuss the expanded utilization of endoscopic transorbital route for intracranial intradural lesions. The goal of this cadaveric study is to assess the feasibility of endoscopic transorbital transtentorial approach for exposure of middle incisural space.

METHODS

Anatomical dissections were performed in four human cadaveric heads (8 sides) using 0- and 30-degree endoscopes. A stepwise description of endoscopic transorbital transtentorial approach to middle incisural space and related anatomy was provided.

RESULTS

Orbital manipulation following superior eyelid crease incision with lateral canthotomy and cantholysis established space for bone drilling. Extradural stage consisted of extensive drilling of orbital roof of frontal bone, lessor, and greater wings of sphenoid bone. Intradural stage was composed of dissection of sphenoidal compartment of Sylvian fissure, lateral mobilization of mesial temporal lobe, and penetration of tentorium. A cross-shaped incision of tentorium provided direct visualization of crural cistern with anterolateral aspect of cerebral peduncle and upper pons. Interpeduncular cistern, prepontine cistern, and anterior portions of ambient and cerebellopontine cisterns were exposed by 30-degree endoscope.

CONCLUSION

The endoscopic transorbital transtentorial approach can be used as a minimally invasive surgery for exposure of middle incisural space. Extensive drilling of sphenoid wing and lateral mobilization of mesial temporal lobe are the main determinants of successful dissection. Further studies are needed to confirm the clinical feasibility of this novel approach.

Pure Endoscopic Lateral Orbitotomy Approach to the Cavernous Sinus, Posterior, and Infratemporal Fossae: Anatomic Study

Objective  The aim of this anatomic study is to describe a fully endoscopic lateral orbitotomy extradural approach to the cavernous sinus, posterior, and infratemporal fossae. Material and Methods  Three prefixed latex-injected head specimens (six orbital exposures) were used in the study. Before and after dissection, a computed tomography scan was performed on each cadaver head and a neuronavigation system was used to guide the approach. The extent of bone removal and the area of exposure of the targeted corridor were evaluated with the aid of OsiriX software (Pixmeo, Bernex, Switzerland). Results  The lateral orbital approach offers four main endoscopic extradural routes: the anteromedial, posteromedial, posterior, and inferior. The anteromedial route allows a direct route to the optic canal by removal of the anterior clinoid process, whereas the posteromedial route allows for exposure of the lateral wall of the cavernous sinus. The posterior route is targeted to Meckel's cave and provides access to the posterior cranial fossa by exposure and drilling of the petrous apex, whereas the inferior route gives access to the pterygopalatine and infratemporal fossae by drilling the floor of the middle cranial fossa and the bone between the second and third branches of the trigeminal nerve. Conclusion  The lateral orbitotomy endoscopic approach provides direct access to the cavernous sinus, posterior, and infratemporal fossae. Advantages of the approach include a favorable angle of attack, minimal brain retraction, and the possibility of dissection within the two dural layers of the cavernous sinus without entering its neurovascular compartment.

Endoscopic transorbital route to the petrous apex: a feasibility anatomic study

BACKGROUND

While the subtemporal approach represents the surgical module milestone designed to reach the petrous apex, a novel ventral route, which is the superior eyelid endoscopic transorbital approach, has been proposed to access the skull base. Accordingly, we aimed to evaluate the feasibility of this route to the petrous apex, providing a qualitative and quantitative analysis of this relatively novel pathway.

METHODS

Five human cadaveric heads were dissected at the Laboratory of Surgical NeuroAnatomy of the University of Barcelona. After proper dissection planning, anterior petrosectomy via the endoscopic transorbital route was performed. Specific quantitative analysis, as well as dedicated three-dimensional reconstruction, was done.

RESULTS

Using the endoscopic transorbital approach, it was possible to reach the petrous apex with an average volume bone removal of 1.33 ± 0.21 cm³. Three main intradural spaces were exposed: cerebellopontine angle, middle tentorial incisura, and ventral brainstem. The first one was bounded by the origin of the trigeminal nerve medially and the facial and vestibulocochlear nerves laterally, the second extended from the origin of the oculomotor nerve to the entrance of the trochlear nerve into the tentorium free edge while the ventral brainstem area was hardly accessible through the straight, ventral endoscopic transorbital trajectory.

CONCLUSION

This is the first qualitative and quantitative anatomic study concerning details of the lateral aspect of the incisura and ventrolateral posterior fossa reached via the transorbital window. This manuscript is intended as a feasibility anatomic study, and further clinical contributions are mandatory to confirm the effectiveness of this approach, defining its possible role in the neurosurgical armamentarium.

Transnasal Endoscopic and Lateral Approaches to the Clivus: A Quantitative Anatomic Study

BACKGROUND

Transnasal endoscopic approaches to the clivus have been established recently. Comparative analyses with classic lateral approaches are limited. In this study, we compared transnasal endoscopic and lateral approaches to the clivus, quantifying the exposure and working volume of each approach in the anatomy laboratory.

METHODS

High-resolution computed tomography scans were performed on 5 injected specimens (10 sides). In each specimen, transnasal endoscopic approaches (i.e., paraseptal, transrostral, extended transrostral, transethmoidal, and extended transclival without and with intradural hypophysiopexy) and lateral approaches (i.e., retrosigmoid, far-lateral, presigmoid retrolabyrinthine and translabyrinthine) to the clivus were performed. An optic neuronavigation system and dedicated software (ApproachViewer; Guided Therapeutics Program, University Health Network, Toronto, Ontario, Canada) were used to quantify the working volume and exposed clival area of each approach. Statistical evaluation was performed with the Kruskal-Wallis test and Steel-Dwass-Critchlow-Fligner post hoc test.

RESULTS

Endoscopic transnasal transclival approaches showed higher working volume and larger clival exposure compared with lateral approaches. Incremental volumetric values were evident for transnasal approaches; presigmoid approaches provided less working volume than retrosigmoid approaches. A transnasal transclival approach with hypophysiopexy provided significant exposure of the upper clivus (84.4%). The transrostral approach was the first transnasal approach providing satisfactory access to the midclivus (66%); retrosigmoid and far-lateral approaches provided exposure of approximately one half of the midclivus. The lower clivus was optimally exposed with endoscopic transclival approaches (83%), whereas access to this region was limited with lateral approaches.

CONCLUSIONS

This quantitative anatomic study shows that endoscopic transnasal approaches to the clivus provide a larger working volume and wider exposure of the clivus compared with lateral approaches.

Quantitative comparison of cranial approaches in the anatomy laboratory: A neuronavigation based research method

AIM

To describe the development and validation of a novel neuronavigation-based method, which allows the quantification of the anatomical features that define an approach, as well as real-time visualization of the surgical pyramid.

METHODS

The method was initially developed with commercially-available hardware for coordinate collection (a digitizer and a frameless navigation system) and software for volume rendering; dedicated neuronavigation software (ApproachViewer, part of GTx-UHN) was then developed. The accuracy of measurements and the possibility of volumetric rendering of surgical approaches simulated in a phantom were compared among three different methods and commercially-available radiological software. In the anatomy laboratory, ApproachViewer was applied to the comparative quantitative analysis of multiple neurosurgical approaches and was used by many surgeons who were untrained for the research method.

RESULTS

The accuracy of ApproachViewer is comparable to commercially-available radiological software. In the anatomy laboratory, the method appears versatile. The system can be easily used after brief training. ApproachViewer allows for real-time evaluation and comparison of surgical approaches, as well as post-dissection analyses of collected data. The accuracy of the method depends on the navigation registration: with a 1-2 mm registration error, it is adequate for evaluation and comparison of most neurosurgical approaches.

CONCLUSION

This new research method and software allows semi-automated visualization, quantification, and comparison of neurosurgical approaches in the anatomy laboratory.

Transorbital endoscopic approach for exposure of the sylvian fissure, middle cerebral artery and crural cistern: an anatomical study

BACKGROUND

The availability of minimal access instrumentation and endoscopic visualization has revolutionized the field of minimally invasive skull base surgery. The transorbital endoscopic approach using an eyelid incision has been proposed as a new minimally invasive technique for the treatment of skull base pathology, mostly extradural tumors. Our study aims to evaluate the anatomical aspects and potential role of the transorbital endoscopic approach for exposure of the sylvian fissure, middle cerebral artery and crural cistern.

METHODS

An anatomical dissection was performed in four freshly injected cadaver heads (8 orbits) using 0- and 30-degree endoscopes. First, an endoscopic endonasal medial orbital decompression was done to facilitate medial retraction of the orbit. An endoscopic transorbital approach through an eyelid incision, with drilling of the posterior wall of the orbit and lesser sphenoidal wing, was then performed to expose the sylvian fissure and crural cisterns. A stepwise anatomical description of the approach and visualized anatomy is detailed.

RESULTS

A superior eyelid incision followed by orbital retraction provided a surgical window of approximately 1.2 cm (range 1.0-1.5 cm) for endoscopic transorbital dissection. The superior (SOF) and inferior (IOF) orbital fissures represent the medial limits of the approach and are identified in the initial part of the procedure. Drilling of the orbital roof (lateral and superior to the SOF), greater sphenoidal wing (lateral to the SOF and IOF) and lesser sphenoidal wing exposed the anterior and middle fossa dura. A square-shaped dural opening provided visualization of the posterior orbital gyri, sylvian fissure and temporal pole. Intradural dissection allowed exposure of the sphenoidal portion of the sylvian fissure, M1, MCA bifurcation and M2 branches and lenticulostriate perforators. Dissection of the medial aspect of the sylvian and carotid cisterns with a 30-degree endoscope allowed exposure of the mesial temporal lobe and crural cistern.

CONCLUSIONS

The transorbital endoscopic approach allows successful exposure of the sphenoidal portion of the sylvian fissure and M1 and M2 segments of the middle cerebral artery. Angled endoscopes may provide visualization of the mesial temporal lobe and crural cistern. Although our anatomical study demonstrates the feasibility of intradural dissection and closure via an endoscopic transorbital approach, further studies are necessary to evaluate its role in the clinical scenario.

A Side Door to Meckel's Cave: Anatomic Feasibility Study for the Lateral Transorbital Approach

BACKGROUND: In the last decade, endoscopic skull base surgery has significantly developed and generated a plethora of techniques and approaches for access to the cranial ventral floor. However, the exploration for the least-aggressive, maximally efficient approach continues.

OBJECTIVE: To describe in detail an anatomical study, along with the technical nuances of a novel endoscopic approach to Meckel's Cave (MC) using a lateral transorbital (LTO) route.

METHODS: Eighteen orbits of injected cadaveric specimens were operated on, using an endoscopic LTO approach to MC, middle cranial fossa, and paramedian skull base preserving the orbital rim. Surgical navigation and an after-the-fact infratemporal craniectomy were utilized to identify the limits of the approach.

RESULTS: Following a transorbital approach opening a trapezoid window at the superolateral aspect (average 166.7 mm2), a middle fossa “peeling” and full visualization of MC was accomplished with no difficulties in all specimens. The entire approach was performed extradurally without the need to expose the temporal lobe.

CONCLUSION: In a cadaveric model, the endoscopic LTO approach affords a direct route to access MC. Its main advantage is that it is minimally disruptive in nature, less brain retraction is required, and it reaches the middle fossa in an anterolateral perspective. It also requires no manipulation of the temporalis muscle, limited cosmetic incision, and rapid recovery. It seems a viable alternative to traditional approaches for lesions lateral to the cranial nerves at the cavernous sinus and MC, that is, schwannomas. Clinical utilization of this approach will challenge its efficacy and identify limitations.