Endoscopic endonasal approach to the middle cranial fossa through the cavernous sinus triangles: anatomical considerations

Anterolateral surgical triangle of the cavernous sinus: a cadaveric study of neurosurgical importance

BACKGROUND

The anterolateral triangle around the cavernous sinus is a surgical skull base triangle used as a neurosurgical landmark essential to skull-based surgeries. There are few reports of its measurements with little attention paid to anatomical variations.

METHODOLOGY

A total of 15 adult human cadaveric skulls were dissected to expose the anterolateral triangle on both sides. The triangle was defined and measurements of the three borders were taken precisely and the area of each triangle was calculated using Heron's formula.

RESULTS

On an average, the length of the anteromedial border is 11.4 (+ 2.2 mm); the length of the posteromedial border is 8.7 (+ 2.6 mm); the length of the lateral border is 13.06 (+ 2.6 mm) and the area of the anterolateral triangle is 48.05 (+ 17.5 mm2).

CONCLUSION

Concise understanding of anterolateral triangle is essential to skull-based surgeries; comprehending its anatomy helps with better surgical planning and provides insight into local pathology.

Endonasal Endoscopic Anatomy of the Orbito-Cavernous-Pterygopalatine Interface: Multilayer Anatomical Description and Landmarks to Define the Limits of the Compartments

BACKGROUND

Despite growing interest in the endoscopic endonasal approach (EEA) to the medial orbital apex (OA), a comprehensive description of the multilayer topology lying at the intersection of the regional compartments is missing.

METHODS

An EEA to the OA, pterygopalatine fossa, and cavernous sinus was performed in 20 specimens. A 360° layer-by-layer dissection was performed taking into consideration relevant anatomical aspects of the interface and documented with 3-dimensional technologies. Endoscopic landmarks were analyzed to provide an outline of the compartments and identify critical structures. Additionally, the consistency of a previously described reference called orbital apex convergence prominence was analyzed and a method to identify its position was introduced.

RESULTS

The orbital apex convergence prominence was an inconsistent finding (15%). However, a craniometric method introduced in this study proved to be reliable to reach the orbital apex convergence point. Additional structures such as the sphenoethmoidal suture and a 3-suture junction (sphenoethmoidal-palatoethmoidal-palatosphenoidal) helped to identify the posterior limit of the OA and define a keyhole to access the compartments of the interface. We defined the bone limits of the "optic risk zone," an area where the optic nerve is more susceptible to damage. Furthermore, an orbital fusion line (periorbita-dura-periosteum) was identified and divided into 4 segments according to adjacent structures: optic, cavernous, pterygopalatine, and infraorbital.

CONCLUSIONS

Understanding cranial landmarks and the folds of the layers covering the orbito-cavernous-pterygopalatine interface can facilitate tailoring an EEA to the medial orbital space and avoid unnecessary exposure of sensitive anatomy in the vicinity.

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.

A Novel Sublabial Anterior Transmaxillary Approach for Medically Refractory Mesial Temporal Lobe Epilepsy: A Comparative Anatomic Study

BACKGROUND

Current approaches for mesial temporal lobe epilepsy may result in suboptimal seizure control and cognitive decline. An incomplete treatment of the epileptogenic zone and unnecessary violation of functional cortical and subcortical areas may contribute to suboptimal results.

OBJECTIVE

To describe and test the anatomic feasibility of a novel endoscopic anterior transmaxillary (ATM) approach to the temporal lobe and to compare the described technique to other transfacial approaches.

METHODS

Twenty-four cadaveric brain hemispheres fixed in formalin were used to study anterior temporal surface anatomy. Two additional hemispheres were fixed in formalin and then frozen for white matter dissections. Subsequently, bilateral dissections on 4 injected cadaveric heads were used to describe the endoscopic ATM approach and to evaluate various anterior endoscopic corridors for the temporal pole and mesial temporal lobe structures.

RESULTS

The ATM approach was considered superior because of direct visualization of the temporal pole and natural alignment with the mesial temporal structures. The mean exposure corridor covered 49.1° in the sagittal plane and 66.2° in the axial plane. The ATM allowed direct access lateral to the maxillary and mandibular nerves with an anterior-posterior trajectory aligned to the longitudinal axis of the hippocampus formation, allowing for a selective amygdalohippocampectomy with preservation of the trigeminal branches and the lateral temporal neocortex.

CONCLUSION

The ATM approach is anatomically feasible, providing a direct and selective approach for the temporal pole and mesial temporal lobe structures, with a substantial angle of visualization because of its direct alignment with the mesial temporal lobe structures.

Endoscopic Transnasal Transmaxillary Approach to Orbital Apex through the Meningo-Orbital Band: A Cadaveric Feasibility Study

Background

Extradural transcranial release of the meningo-orbital band occupying the lateral part of the superior orbital fissure is used to approach the orbital apex and middle cranial fossa. The authors tested the feasibility of the release of the meningo-orbital band via an endonasal transmaxillary approach.

Materials and Methods

Five injected cadaveric heads were assessed for dimensions of superior orbital fissure by computerized tomography. An endonasal transsphenoid transpterygoid approach was done to the superior orbital fissure and annulus of Zinn medially, down to the maxillary nerve. The periorbita was dissected superolaterally to expose the greater wing of the sphenoid and the meningo-orbital band. The superior orbital fissure was decompressed inferiorly by drilling the greater wing of the sphenoid and the maxillary strut after transposition of the maxillary nerve. The meningoorbital band was cut at the junction of the lateral part of the superior orbital fissure and the periorbita exposing the frontotemporal dural junction. The edge of the lesser wing of the sphenoid was drilled toward the annulus of Zinn and the optic canal. The temporal lobe dura was separated from the periorbita and lateral cavernous dural wall at the meningo-orbital band and the ophthalmic nerve.

Results

The superior orbital fissure had an oblique angle (mean: 39 ± 2.75 degrees) to the midsagittal plane, the length of its lateral part corresponding to the meningo-orbital band was (mean: 6.08 ± 2.58 mm) and the distance from its lateral end to midline was (mean 2.97 ± 0.11 cm). The meningo-orbital band was released in 10 cadaveric head sides with a distinct plane between the periorbita and the dura propria. Transmaxillary endoscopy provided less orbital retraction and better visualization of the lateral wall of the cavernous sinus.

Conclusion

Endonasal transmaxillary release of the meningoorbital band is feasible, allowing exposure of the orbital apex and the middle cranial fossa.

The orbitopterygoid corridor as a deep keyhole for endoscopic access to the paranasal sinuses and clivus

OBJECTIVE

The anteromedial triangle (AMT) is the triangle formed by the ophthalmic (V1) and maxillary (V2) nerves. Opening of this bony space offers a limited access to the sphenoid sinus (SphS). This study aims to demonstrate the utility of the orbitopterygopalatine corridor (OPC), obtained by enlarging the AMT and transposing the contents of the pterygopalatine fossa (PPF) and V2, as an entrance to the SphS, maxillary sinus (MaxS), and nasal cavity.

METHODS

Five formalin-injected cadaveric specimens were used for this study (10 approaches). A classic pterional approach was performed. An OPC was created through the inferior orbital fissure, between the orbit and the PPF, by transposing the PPF inferiorly. The extent of the OPC was measured using neuronavigation and manual measurements. Two illustrative cases using the OPC to access skull base tumors are presented in the body of the article.

RESULTS

Via the OPC, the SphS, MaxS, ethmoid sinus (EthS), and nasal cavity could be accessed. The use of endoscopic assistance through the OPC achieved better visualization of the EthS, SphS, MaxS, clivus, and nasal cavity. A significant gain in the area of exposure could be achieved using the OPC compared to the AMT (22.4 mm2 vs 504.1 mm2).

CONCLUSIONS

Opening of the AMT and transposition of V2 and the contents of the PPF creates the OPC, a potentially useful deep keyhole to access the paranasal sinuses and clival region through a middle fossa approach. It is a valuable alternative approach to reach deep-seated skull base lesions infiltrating the cavernous sinus and middle cranial fossa and extending into the paranasal sinus.

The endoscopic transpterional port approach: anatomy, technique, and initial clinical experience

OBJECTIVE

The evolution of microsurgical and endoscopic techniques has allowed the development of less invasive transcranial approaches. The authors describe a purely endoscopic transpterional port craniotomy to access lesions involving the cavernous sinus and the anterolateral skull base.

METHODS

Through single- or dual-port incisions and with direct endoscopic visualization, the authors performed an endoscopic transpterional port approach (ETPA) using a 4-mm straight endoscope in 8 sides of 4 formalin-fixed cadaveric heads injected with colored latex. A main working port incision is made just below the superior temporal line and behind the hairline. An optional 0.5- to 1-cm second skin port incision is made on the lateral supraorbital region, allowing multiangle endoscopic visualization and maneuverability. A 1.5- to 2-cm craniotomy centered over the pterion is done through the main port, which allows an extradural exposure of the cavernous sinus region and extra/intradural exposure of the frontal and temporal cranial fossae. The authors present a pilot surgical series of 17 ETPA procedures and analyze the surgical indications and clinical outcomes retrospectively.

RESULTS

The initial stage of this work on cadavers provided familiarity with the technique, standardized its steps, and showed its anatomical limits. The clinical ETPA was applied to gain access into the cavernous sinus, as well as for aneurysm clipping and meningioma resection. Overall, perioperative complications occurred in 1 patient (6%), there was no mortality, and at last follow-up all patients had a modified Rankin Scale score of 0 or 1.

CONCLUSIONS

The ETPA provides a less invasive, focused, and direct route to the cavernous sinus, and to the frontal and temporal cranial fossae, and it is feasible in clinical practice for selected indications with good results.

The Endoscopic Endonasal Transmaxillary Approach to Meckel's Cave Through the Inferior Orbital Fissure

BACKGROUND

Surgical access to Meckel's Cave (MC) is challenging due to its deep location and surrounding important neurovascular structures. Currently existing endoscopic endonasal (EE) approaches require dissecting near the internal carotid artery (ICA) or require transposition of the pterygopalatine neurovascular bundle.

OBJECTIVE

To describe a novel approach to access the anterolateral aspect of the MC using a minimally invasive EE route.

METHODS

The EE transmaxillary transinferior orbital fissure approach was simulated in 10 specimens. The approach included an ethmoidectomy followed by an extended medial maxillectomy with transposition of the nasolacrimal duct. The infraorbital fissure was opened, and the infraorbital neurovascular bundle was transposed inferiorly. A quadrilateral space, bound by the maxillary nerve inferomedially, ophthalmic nerve superomedially, infraorbital nerve inferolaterally, and floor of the orbit superolaterally, was exposed. The distances from the foramen rotundum (FR) to the ICA, orbital apex (OA), and infratemporal crest (ITC) and from the OA to the ICA and ITC were measured.

RESULTS

The distances obtained were FR-ICA = 19.42 ± 2.03 mm, FR-ITC = 18.76 ± 1.75 mm, FR-OA = 8.54 ± 1.34 mm, OA-ITC = 19.78 ± 2.63 mm, and OA-ICA = 20.64 ± 142 mm. Two imaginary lines defining safety boundaries were observed between the paraclival ICA and OA, and between the OA and ITC (safety lines 1 and 2).

CONCLUSION

The reported approach provides a less invasive route compared to contemporary approaches, allowing expanded views and manipulation anteromedial and anterolateral to MC. It may be safer than the existing approaches as it does not require transposition of the ICA, infratemporal fossa, and pterygopalatine fossa, and allows access to tumors located anteriorly on the floor of the middle cranial fossa.

Endoscopic Endonasal Approach to the Lateral Wall of the Cavernous Sinus: A Cadaveric Feasibility Study

OBJECTIVE:

A transcranial extradural approach to the middle cranial fossa (MCF) requires separation of the dural layers of the lateral wall of the cavernous sinus. The authors tested the feasibility of an endonasal approach for this separation.

METHODS:

A cadaveric feasibility study was conducted on the sides of 14 dry skulls and 10 fresh cadaveric heads. An endonasal, transsphenoidal, transpterygoid approach was taken to the MCF. The maxillary struts and medial greater wing of the sphenoid below the superior orbital fissure were drilled with transposition of the maxillary nerve. The lateral cavernous dural layers were split at the maxillary nerve with separation of the temporal lobe dura and exposure of the MCF bony base. The integrity of the cranial nerves and inner and outer dural layers of the lateral cavernous wall was checked. Different measurements of bony landmarks were obtained.

RESULTS:

The integrity of the dural layers of the lateral cavernous wall and the cranial nerves were preserved in 10 heads. The mean area of the bony corridor was 4.68 ± 0.97 cm², the V2-to-V3 distance was 15.21 ± 3.36 mm medially and 18.21 ± 3.45 mm laterally, and the vidian canal length was 13.01 ± 3.06 mm.

CONCLUSIONS:

Endonasal endoscopic separation of the lateral cavernous dural layers is feasible without crossing the motor cranial nerves, allowing better exposure of the MCF.

Endoscopic Endonasal Repair of Cerebrospinal Fluid Leakage Caused by a Rare Traumatic Clival Fracture

An 89-year-old male presented with cerebrospinal fluid (CSF) rhinorrhea associated with head trauma sustained as a pedestrian in a traffic accident. Computed tomography (CT) showed pneumocephalus and multiple cranial bone fractures, including the clivus. Although the CSF rhinorrhea was treated conservatively for a week, clinical symptoms did not improve and surgical repair was performed. Preoperative thin-sliced bone CT and steady-state magnetic resonance images revealed a bone defect at the middle clivus and a collection of CSF fluid from the clival fistula in the sphenoid sinus. Endoscopic endonasal reconstruction was performed, and the 3-mm diameter dural tear and bone defect at the middle clivus were well visualized. The fistula was repaired using a pedicled nasoseptal mucosal flap. The CSF rhinorrhea completely disappeared as a result of the endoscopic endonasal surgery. The present report describes a rare case of CSF rhinorrhea caused by a traumatic clival fracture and surgical management by endoscopic endonasal surgery.