Endoscopic Approaches to the Paramedian Skull Base: An Anatomic Comparison of Contralateral Endonasal and Transmaxillary Strategies.

BACKGROUND: The expanded endoscopic endonasal approach (EEA) is limited laterally by the internal carotid artery (ICA). The EEA to the paramedian skull base often requires complex maneuvers such as dissection of the Eustachian tube (ET) and foramen lacerum (FL), and ICA manipulation. An endoscopic contralateral transmaxillary approach (CTMA) has the potential to provide adequate exposure of the paramedian skull base while bypassing manipulation of the aforementioned anatomic structures. OBJECTIVE: To quantify and compare the surgical nuances of a CTMA and a contralateral EEA when approaching the paramedian skull base in cadaveric specimens. METHODS: Five adult cadaveric heads were dissected bilaterally (10 sides) using a contralateral EEA and a CTMA to expose targets of interest at the paramedian skull base. For each target in both approaches, the surgical freedom, angle of attack, the corridor's "perspective angle," and "turning angle" to circumvent the ICA, ET, and FL were obtained. RESULTS: The CTMA achieved superior surgical freedom at all targets ( P < .05) except at the root entry point of cranial nerve XII. The CTMA provided superior vertical and horizontal angles of " attack " to the majority of targets of interest. Except when approaching the root entry point of cranial nerve XII, the CTMA " turning angle " around the ICA, ET, and FL were wider with CTMA for all targets. CONCLUSION: A CTMA complements the EEA to access the paramedian skull base. A CTMA may limit the need for complex maneuvers such as ICA mobilization and dissection of the ET and FL when approaching the paramedian skull base.

Quantitative Comparative Analysis of the Endoscope-Assisted Expanded Retrosigmoid Approach and the Far-Lateral Approach to the Inframeatal Area: An Anatomic Study With Surgical Implications.

BACKGROUND: The inframeatal area (IFMA) is a complex anatomic region of the posterior cranial fossa. Given its deep-seated location, tumors involving the IFMA represent a surgical challenge. OBJECTIVE: To objectively compare the endoscope-assisted expanded retrosigmoid approach (ERSA) and the far-lateral supracondylar transtubercular approach (FLTA) to address the IFMA. METHODS: Anatomic dissections were performed on 5 cadaveric heads (10 sides). The ERSAs were performed before and after the FLTAs. The surgical exposure, surgical freedom, and angles of attack to the IFMA were measured and compared for each approach. In addition, 2 illustrative clinical cases are reported. RESULTS: Compared with FLTA, ERSA yielded a nonsignificantly smaller mean area of exposure, whereas FLTA provided a significantly larger mean area of surgical freedom, compared with ERSA ( P = .002). The mean horizontal and vertical angles of attack were significantly different between the approaches. In the vertical plane, FLTA yielded the broadest angle of attack at the root entry zone of the lower cranial nerves (CN; P < .004), whereas ERSA did so at the dural entry zone of CN VII/VIII ( P = .006). In the horizontal plane, FLTA achieved its broadest angle of attack at the root entry zone of the lower CNs ( P = 1.83) while ERSA at the dural entry zone of CN VII/VIII ( P = .37). CONCLUSION: ERSA and FLTA granted a comparable exposure with the IFMA. Although FLTA may afford a larger area of surgical freedom, ERSA may be a suitable alternative to approach the IFMA, particularly to reach the most medial and superior aspects of this region. Conversely, FLTA may facilitate access to more caudally targets.

The "Crista Ovale": A Reliable Anatomical Landmark in Transorbital Endoscopic Approaches to the Middle Cranial Fossa.

BACKGROUND: Transorbital endoscopic approaches (TOEAs) have emerged as adjunct and alternatives for accessing the middle cranial fossa (MCF). Nuances of the skull base anatomy from a ventral transorbital endoscopic viewpoint remain to be fully described. OBJECTIVE: To assess the anatomy of the "crista ovale" (COv), described transcranially as the midsubtemporal ridge (MSR), from a ventral transorbital perspective and evaluate its role as a landmark in TOEA to the MCF. METHODS: Lateral TOEAs to the MCF were performed in 20 adult cadaveric heads (40 sides). The presence of the COv/MSR was evaluated under endoscopic visualization. Anatomic relationships between COv/MSR and surrounding structures were assessed. The presence of COv/MSR was also examined in 30 cadaveric head computed tomography (CT) scans (60 sides). RESULTS: The COv/MSR was identified in 98% (39/40) of sides at the MCF, as 1 of 4 major configurations. The COv/MSR was found anterolateral to the foramen ovale and foramen spinosum (mean distance: 9.2 ± SD 2.4 mm and 12.3 ± SD 2.6 mm, respectively) directly anterior or anteromedial to the petrous apex (mean distance: 26.2 ± SD 2.6 mm) and at a mean 47.6 ± SD 4.7 mm from the approach's surgical portal. It was recognized in 95% (57/60) of CT scans. CONCLUSION: The COv/MSR can be readily identified during TOEA to the MCF and on CT. It serves as a reliable landmark to localize the foramen ovale, foramen spinosum, and petrous apex. Further studies may confirm its surgical significance in transorbital endoscopic procedures.

Transorbital Approach for Olfactory Groove Meningioma.

The transorbital endoscopic approach has been increasingly employed in the management of skull base disease.1-4 We present a case of a 48-year-old woman with a 2-month history of progressively worsening headache referred to our neurosurgery division after a new-onset generalized seizure. On examination, she was found to have diminished olfaction with no additional findings, including no visual or cognitive deficits. Preoperative imaging revealed a large anterior fossa mass originating at the left olfactory groove with leftward extension and prominent anterior and posterior ethmoidal arterial feeders. A left-sided transorbital approach was planned to address the tumor. The lesion was resected without incident using a pure transorbital endoscopic technique. The microscope was brought into the field at the end of the procedure to aid with hemostasis of the surgical bed. The patient recovered without surgical complications. Histopathology revealed a World Health Organization grade I olfactory groove meningioma. Postoperative imaging confirmed gross total tumor resection without evidence of recurrence. This case highlights the application of the transorbital endoscopic approach in the management of anterior cranial base tumors. Advantages of this approach include minimal invasive access, avoidance of brain retraction, and ease for early tumor devascularization.

Squamous Cell Carcinoma of the Temporal Bone Arising from Cholesteatoma: A Case Report and Review of the Literature.

Objective Present a case of squamous cell carcinoma of the temporal bone (SCCTB) arising in a 61-year-old female with a prior history of cholesteatoma and persistent otologic symptoms and review the current literature regarding this disease presentation. Setting Tertiary academic center. Patient A 61-year-old female with a history of left ear cholesteatoma for which she had undergone surgery 54 years prior. The patient presented with a persistent history of otorrhea since first surgery and developed exacerbation of symptoms just prior to presentation at our department. The clinical picture was highly suspicious of cholesteatoma recurrence. However, the biopsy was consistent with squamous cell carcinoma. Intervention Surgical debulking of the lesion was followed by a brief course of radiation therapy later halted by the patient due to side effect intolerance. Conclusion SCCTB may arise from cholesteatoma. A high index of suspicion for SCCTB should be maintained in patients with a prior history of cholesteatoma and evidence of a temporal bone mass with persistent otologic symptoms.

Transorbital Endoscopic Approach for Repair of Frontal Sinus Cerebrospinal Fluid Leaks: Case-Series.

OBJECTIVES: To highlight the feasibility and evaluate the outcomes of the transorbital endoscopic approach (TOEA) in the management of frontal sinus cerebrospinal fluid (CSF) leaks. STUDY DESIGN: Retrospective case series. METHODS: The database of patients with frontal sinus CSF leaks managed with TOEA from January 2017 through December 2019 at our institution was reviewed. Two videos of clinical case examples are presented. RESULTS: Sixteen patients (10 males, 6 females, mean age 53; range 21-61 years) underwent TOEA through the superior eyelid corridor for the repair of frontal sinus CSF leak. The most common etiology of the CSF leak was trauma (nine cases; 56.3%), followed by injury from iatrogenic causes in six cases (37.5%), and spontaneous leak in one case (6.2%). Average defect size was 8.8 mm (range 2.0-20.8 mm). Ten patients were revision cases who had undergone prior nontransorbital CSF leak repair at outside institutions. All patients underwent successful repair via TOEA without postoperative complications. Complete resolution was maintained in all cases. Mean follow-up period was 11 months (range 6-22 months). CONCLUSIONS: TOEA is a safe minimally disruptive alternative for definitive management of frontal sinus CSF leak in well-selected primary or revision cases. Further studies are necessary to define its indications and outcomes. LEVEL OF EVIDENCE: 4 Laryngoscope, 131:1753-1757, 2021.

The Role of Endonasal Endoscopic Optic Nerve Decompression as the Initial Management of Primary Optic Nerve Sheath Meningiomas.

Background The management of optic nerve sheath meningiomas (ONSMs) remains controversial. Surgical decompression through traditional resective techniques has been associated with significant morbidity. While radiation therapy, the current modality of choice is not exempt of risks. Transnasal endoscopic optic nerve decompression (EOND) offers a direct route to the orbit, optic canal, and orbital apex, providing a minimally invasive alternative. Objective The main objective of this article is to assess EOND as the initial management of symptomatic patients with primary ONSM. Methods Patients with ONSMs without a history of radiotherapy who underwent EOND were retrospectively reviewed. Postoperative imaging, duration of follow-up, and visual outcomes at the last ophthalmology visit were assessed. Results Four women (age range 25-63 years) with primary ONSMs that underwent EOND were identified. All patients displayed subjective and objective baseline signs of vision loss. Additionally, baseline proptosis, diplopia, optic nerve atrophy, and ocular pain were identified. In none of the cases, the optic nerve sheath was breached. Following EOND, all patients deferred treatment with adjuvant radiotherapy. At a mean postoperative follow-up of 14 months, all patients were clinically stable without evidence of disease progression on imaging or physical examination. At last ophthalmologic evaluation, three out of four showed objective improvements from baseline visual acuity and visual field (remaining patient had baseline optic nerve atrophy). Conclusion These results suggest that EOND could be a viable initial treatment modality of selected primary ONSM cases. Further studies are warranted to determine long-term efficacy and its role in a stepwise progression of management, preceding radiotherapy.

Comparative Analysis Between Lateral Orbital Rim Preservation and Osteotomy for Transorbital Endoscopic Approaches to the Cavernous Sinus: An Anatomic Study.

BACKGROUND: Transorbital endoscopic approach (TOEA) to the cavernous sinus (CS) is a novel surgical technique. However, the necessity of lateral orbital rim (LOR) osteotomy is questionable. OBJECTIVE: To illustrate the surgical dissection of TOEAs to CS and to investigate the additional benefit of LOR osteotomy. METHODS: Anatomic dissections were carried out in 7 cadaveric heads (14 sides). The TOEAs were performed before and after LOR osteotomy; herein referred as the lateral transorbital approach (LTOA) and the lateral orbital wall approach (LOWA), respectively. The stereotactic measurements of the area of exposure, surgical freedom, and angles of attack around CS were quantified. RESULTS: LOWA increased larger area of exposure than LTOA at entry site (5.3 ± 0.6 cm2 and 2.6 ± 0.6 cm2, respectively; P < .001) but both of these techniques provided similar area of exposure at the surgical target site. With regard to the surgical freedoms, those afforded by LOWA were all significantly superior at all of the surgical targets with the difference ranged from 106.6% to 172.5%. No significant differences were found between the vertical angles produced by either approach. On the other hand, the horizontal angles achieved by LOWA were significantly more favorable. CONCLUSION: The TOEAs, either with or without LOR osteotomy are feasible for CS exposure. Although the incremental effect of maneuverability is attained following the LOR osteotomy, it should be performed selectively. Additional research is needed to further validate the safety and efficacy, as well as for precisely defining the clinical application of these techniques.

Anatomic Nuances of the Ophthalmic Artery Origin from a Ventral Viewpoint: Considerations and Implications for Endoscopic Endonasal Surgery.

BACKGROUND: The origin of the ophthalmic artery is within the surgical field of endoscopic endonasal approaches (EEAs) to the suprasellar and parasellar regions. However, its anatomy from the endoscopic point-of-view has not been adequately elucidated. OBJECTIVE: To highlight the anatomy of the ophthalmic artery origin from an endoscopic endonasal perspective. METHODS: The origin of the ophthalmic artery was studied bilaterally under endoscopic visualization, after performing transplanum/transtubercular EEAs in 17 cadaveric specimens (34 arteries). Anatomic relationships relevant to surgery were evaluated. To complement the cadaveric findings, the ophthalmic artery origin was reviewed in 200 "normal" angiographic studies. RESULTS: On the right side, 70.6% of ophthalmic arteries emerged from the superior aspect, while 17.6% and 11.8% emerged from the superomedial and superolateral aspects of the intradural internal carotid artery, respectively. On the left, 76.5%, 17.6%, and 5.9% of ophthalmic arteries emerged from the superior, superomedial, and superolateral aspects of the internal carotid, respectively. Similar findings were observed on angiography. All ophthalmic arteries emerged at the level of the medial opticocarotid recess. Overall, 47%, 26.5%, and 26.5% of ophthalmic arteries (right and left) were inferolateral, inferior, and inferomedial to the intracranial optic nerve segment, respectively. On both sides, the intracranial length of the ophthalmic artery ranged from 1.5 to 4.5 mm (mean: 2.90 ± standard deviation of 0.74 mm). CONCLUSION: Awareness of the endoscopic nuances of the ophthalmic artery origin is paramount to minimize the risk of sight-threatening neurovascular injury during EEAs to the suprasellar and parasellar regions.

The Eustachian Tube as a Landmark for Early Identification of the Abducens Nerve During Endonasal Transclival Approaches.

BACKGROUND: Expanded endonasal approaches have the potential to injure the abducens nerve (cranial nerve [CN] VI). The nerve's root entry zone (REZ) and cisternal segment (CS) are particularly prone to injury during the clivus resection and dural incision of transclival approaches. OBJECTIVE: To investigate the role of the eustachian tube (ET) as a surgical landmark for the REZ and CS of CN VI. METHODS: Transclival expanded endonasal approaches were performed bilaterally in 6 fresh-frozen cadaveric specimens (12 sides). Anatomic relationships between ET and CN VI were documented with neuronavigation. RESULTS: The mean vertical distance from the inferior brainstem point to the horizontal projection of CN VI REZ, CS midpoint, and interdural segment (ID) were 26.38 mm (95% confidence interval [CI] 17.36-35.4), 38.61 mm (95% CI 25.61-51.61), and 42.68 mm (95% CI 30.14-55.22), respectively. The relative vertical distance from the ET to the horizontal projections of the REZ, CS midpoint, and its ID were 6.43 mm (95% CI 3.25-9.61), 18.66 mm (95% CI 11.52-25.8), and 22.72 mm (95% CI 16.02-29.42), respectively. In the axial plane the angles between the ET and (1) the REZ and its midline horizontal projection point, (2) the midpoint and its midline horizontal projection point, and (3) ID and its midline horizontal projection point were 9.81 ± SD 5.20°, 18.50 ± SD 4.87°, and 24.71 ± SD 6.21°, respectively. CONCLUSION: The ET may serve as a constant landmark to reliably predict the position of the REZ and CS of CN VI.

Surgical simulation of a catastrophic internal carotid artery injury: a laser-sintered model.

BACKGROUND: The catastrophic and rare nature of an internal carotid artery (ICA) injury during endonasal surgery limits training opportunities. Cadaveric and animal simulation models have been proposed, but expense and complicated logistics have limited their adoption. Three-dimensional (3D) printed models are portable, modular, reusable, less costly, and proven to improve psychomotor skills required for managing different lesions. In this study we evaluate the role of a simplified laser-sintered model combined with standardized training in improving the effectiveness of managing an ICA injury endoscopically. METHODS: A 3-mm defect was created in the parasellar carotid canal of a laser-sintered model representing a sphenoid sinus. Artificial blood was directed to simulate the copious bleeding arising from an ICA injury. Twenty otolaryngologists and 26 neurosurgeons, with varying training and experience levels, were individually asked to stop the "bleeding" as they would in a clinical scenario, and provided no other instructions. This was followed by individualized formative training and a second simulation. Volume of blood loss, time to hemostasis, and self-assessed confidence scores were compared. RESULTS: At the end of the study, time to hemostasis was reduced from 105.49 seconds to 40.41 seconds (p < 0.001). The volume of blood loss was reduced from 690 to 272 mL (p < 0.001), and the confidence scores increased in 95.7% of participants, from an average of 3 up to 8. CONCLUSION: This ICA injury model, along with a formal training algorithm, appears to be valuable, realistic, portable, and cost-effective. Significant improvement in all parameters suggests the acquisition of psychomotor skills required to control an ICA injury.

Comparative Analysis of the Exposure and Surgical Freedom of the Endoscopic Extended Minipterional Craniotomy and the Transorbital Endoscopic Approach to the Anterior and Middle Cranial Fossae.

BACKGROUND: Numerous minimally invasive approaches to the skull base have been successively developed. Knowledge of the surgical nuances of a specific approach may facilitate approach selection. This study sought to compare the nuances of an extended version of the minipterional craniotomy (EMPT) with those of the transorbital endoscopic approach (TOEA) to the anterior and middle cranial fossae (ACF and MCF, respectively). OBJECTIVE: To quantitatively analyze and compare the area of exposure and surgical freedom between EMPT and TOEA to the ACF and MCF. METHODS: EMPT and TOEA were carried out in 5 latex-injected cadaveric heads, bilaterally (10 sides). For each approach, the area of exposure, surgical freedom, and angle of attack were obtained with neuronavigation and statistically compared. RESULTS: No significant difference was found between the mean area of exposure of EMPT and TOEA at the ACF and MCF (P = .709 and .317, respectively). The mean exposure area at the ACF was of 13.4 ± 2.6 cm2 (mean ± standard deviation) and 13.0 ± 1.9 cm2 for EMPT and TOEA, respectively. Except for the crista galli, EMPT afforded a larger area of surgical freedom at all targets. EMPT also achieved significantly greater attack angles in vertical axis except to the crista galli. The horizontal attack angles to all targets were similar between approaches. CONCLUSION: EMPT and TOEA offer a comparable area of exposure at the ACF and MCF in the cadaver; however, the instrument maneuverability afforded by EMPT is superior. Further studies are necessary to better define their precise surgical application.

Expanded Endoscopic Endonasal Approach to the Inframeatal Area: Anatomic Nuances with Surgical Implications.

BACKGROUND/OBJECTIVE: The inframeatal area represents a challenging region for skull base surgeons. Various surgical corridors have been described to access this area and frequently are used in combination. Recent studies describe the expanded endoscopic endonasal approach (EEA) as an established route for midline regions, particularly medial to the internal carotid arteries (ICA). We sought to evaluate the accessibility, maneuverability, and freedom of movement of the expanded endoscopic endonasal approach to the inframeatal region. METHODS: An EEA combining a middle and an inferior transclival corridor with an infrapetrous and a supracondylar lateral expansion was performed in 5 embalmed human cadaveric heads. The area of exposure and the surgical freedom to access the inframeatal area were calculated. The angle of attack and distances from the lacerum segment of the ICA to several anatomical targets also were measured. Our database was searched to select clinical case examples. RESULTS: The EEA provided an exposure area of 101.26 ± 16.66 mm2 and an area of surgical freedom of 1208.50 ± 507.01 mm2. The angles of attack in both the sagittal and axial planes were wider at the lacerum segment of the ICA and narrower at the dural entrance zone of cranial nerves VII/VIII. Three chondrosarcomas are presented as case illustrations. CONCLUSIONS: The EEA is a feasible route to the inframeatal area. This approach provides a safe working corridor for lesions in this region, as shown by the anatomical and clinical findings presented here. Comparative studies and large case series are warranted to further establish its clinical value.

Quantitative analysis of the surgical exposure and surgical freedom between transcranial and transorbital endoscopic anterior petrosectomies to the posterior fossa.

OBJECT: This study proposes a variation of the transorbital endoscopic approach (TOEA) that uses the lateral orbit as the primary surgical corridor, in a minimally invasive fashion, for the posterior fossa (PF) access. The versatility of this technique was quantitatively analyzed in comparison with the anterior transpetrosal approach (ATPA), which is commonly used for managing lesions in the PF. METHODS: Anatomical dissections were carried out in 5 latex-injected human cadaveric heads (10 sides). During dissection, the PF was first accessed by TOEAs through the anterior petrosectomy, both with and without lateral orbital rim osteotomies (herein referred as the lateral transorbital approach [LTOA] and the lateral orbital wall approach [LOWA], respectively). ATPAs were performed following the orbital approaches. The stereotactic measurements of the area of exposure, surgical freedom, and angles of attack to 5 anatomical targets were obtained for statistical comparison by the neuronavigator. RESULTS: The LTOA provided the smallest area of exposure (1.51 ± 0.5 cm2, p = 0.07), while areas of exposure were similar between LOWA and ATPA (1.99 ± 0.7 cm2 and 2.01 ± 1.0 cm2, respectively; p = 0.99). ATPA had the largest surgical freedom, whereas that of LTOA was the most restricted. Similarly, for all targets, the vertical and horizontal angles of attack achieved with ATPA were significantly broader than those achieved with LTOA. However, in LOWA, the removal of the lateral orbital rim allowed a broader range of movement in the horizontal plane, thus granting a similar horizontal angle for 3 of the 5 targets in comparison with ATPA. CONCLUSIONS: The TOEAs using the lateral orbital corridor for PF access are feasible techniques that may provide a comparable surgical exposure to the ATPA. Furthermore, the removal of the orbital rim showed an additional benefit in an enhancement of the surgical maneuverability in the PF.

Endonasal anatomy of the olfactory neural network: Surgical implications.

OBJECTIVES/HYPOTHESIS: Define the anatomic distribution of the olfactory filaments within specific mucosal regions of the nasal cavity. STUDY DESIGN: Cadaveric study. METHODS: Seventeen cadaveric specimens (34 sides) were dissected to study the anatomical distribution and density of olfactory fila within different regions of the nasal cavity. Olfactory fila were dissected retrogradely to their point of entry into the anterior cranial fossa through the cribriform plate. Anatomic relationships among various components of the olfactory system and their corresponding arterial supply were determined subjectively. RESULTS: The highest density of olfactory fila was found at the mucosa of the ethmoid roof and superior turbinates. Olfactory fila were found at regions not previously considered to be part of the olfactory system: lateral wall of the nose, ethmoidal bullae, and between the os sphenoidale and arc of the posterior choana. Furthermore, at the septum, 20% of the olfactory fila crossed contralaterally before exiting the nose. The anterior ethmoidal arteries were the primary blood supply to the olfactory epithelium. CONCLUSIONS: This study suggests that olfactory filaments extend beyond previously established boundaries. These findings may have clinical implications regarding oncologic resections and could serve as the foundation for the development of techniques that better preserve olfactory function. LEVEL OF EVIDENCE: NA Laryngoscope, 2473-2477, 2018.

Analysis of the far-medial transoral endoscopic approach to the infratemporal fossa.

OBJECTIVES/HYPOTHESIS: To demonstrate anatomic relationships of the far-medial transoral endoscopic assisted approach (FMT-EAA) to the infratemporal fossa (ITF) and define the corridor dimensions, surgical freedom, and limitations associated with this approach. STUDY DESIGN: Cadaveric study. METHODS: Twenty ITFs (10 specimens) were dissected with the assistance of 0 °, 30 °, and 45 ° rod-lens endoscopes. Image guidance was used to confirm and measure the corridors' structural boundaries and document the anatomical relationships encountered in this approach. RESULTS: Access to the ITF via the FMT-EAA can be divided into two secondary surgical corridors: the superomedial and inferolateral triangles, each of which provides access to different areas. The superomedial triangle is bounded medially by the lateral pterygoid plate and posterolateral maxillary sinus wall, superiorly by the greater sphenoid wing, and inferolaterally by the lateral pterygoid muscle. The inferolateral triangle is bounded superiorly by the lower head of the lateral pterygoid muscle, inferiorly by the medial pterygoid muscle, and laterally by the mandible. Using a standard 19-mm endoscope, the FMT-EAA achieves a mean surgical freedom of 231 mm and 161 mm in the vertical and horizontal planes, respectively. CONCLUSIONS: FMT-EAA adequately exposes critical structures of the ITF. This technique is a viable option for the management of selected ITF lesions, either alone or in combination with alternative minimally invasive approaches to the region. LEVEL OF EVIDENCE: NA Laryngoscope, 128:2273-2281, 2018.