Novel Strategies for Expanding the Endoscopic Caudal Access to the Craniovertebral Junction: A Cadaveric Comparative Analysis of Nasofrontal Trephination and Posterior Palatectomy

Abstract

Objectives

Although the endoscopic endonasal approach (EEA) has emerged as a preferred alternative to traditional transoral access for craniovertebral junction (CVJ) surgery, its limited inferior reach beyond the C1 level remains a significant challenge. This study investigates the effectiveness of using a contralateral nasofrontal trephination (CNT) or a posterior palatectomy (PP) to enhance the caudal reach to the CVJ region.

Design

A quantitative cadaveric study.

Setting

Cadaver dissection laboratory.

Participants

A total of 15 adult human cadaveric heads.

Methods

EEA, EEA + PP, and EEA + CNT approaches to the CVJ were performed. Neuronavigation was used for objective measurements quantifying the volume of surgical freedom, surface area of deep exposure, entry point sagittal angle, and inferior reach below the odontoid process.

Main Outcome Measures and Results

EEA + CNT demonstrated superior surgical metrics across all parameters. Surface exposure was significantly greater with EEA + CNT (107.04 cm²) versus EEA + PP (86.26 cm²) and standard EEA (69.78 cm²; p < 0.001). The volume of surgical freedom showed similar superiority with EEA + CNT (60.21 cm³), followed by EEA + PP (34.14 cm³) and EEA (26.13 cm³; p < 0.001). Inferior reach below the odontoid (CNT: 6.35 cm; PP: 2.17 cm; EEA: 0.9 cm; p < 0.0001) and surgical trajectory angle (CNT: 50.1 degrees; PP: 21.4 degrees; EEA: 16.6 degrees; p < 0.0001) demonstrated significant stepwise improvements with each adjunct technique.

Conclusion

Both CNT and PP techniques significantly enhance the surgical corridor of traditional EEA for CVJ access. A CNT afforded superior surgical exposure while maintaining minimal invasiveness. PP offers a viable alternative when external incisions are undesired and lesions are confined within the C2–C3 level.

Keywords

3D photogrammetry - craniovertebral junction - endoscopic endonasal approach - endoscopic endonasal odontoidectomy - multiport endoscopic surgery - nasofrontal trephination - posterior palatectomy - quantitative analysis - skull base

Introduction

The transoral trans-pharyngeal approach was historically the mainstay method of accessing the craniovertebral junction (CVJ) in patients with basilar invagination, odontoid fractures, or tumors.[1] However, this technique has drawbacks, presenting an increased risk of aerodigestive tract morbidities, such as postoperative dysphagia associated with nasal regurgitation and aspiration and the need for prolonged nasogastric tube feeding and edema with airway obstruction, all leading to an extended recovery period.[2] [3] Recently, the endoscopic endonasal approach (EEA) has emerged as a minimally invasive alternative for odontoidectomy and anterior decompression of the CVJ. Others have shown that EEA is associated with lower rates of postoperative dysphagia and respiratory complications.[4] [5] The neurologic and quality of life (QOL) outcomes following EEA are equal to those seen with traditional transoral approaches.[6] [7] Also, nasal-specific QOL does not appear adversely affected by EEA.[8] However, the EEA has a higher incidence of cerebrospinal fluid (CSF) leaks, both intraoperative (30%) and postoperative (5.2%), compared with the transoral approach.[9] Conversely, advancements in surgical techniques, including multilayered reconstructions and the application of vascularized flaps, have significantly reduced the incidence of postoperative CSF leaks. These developments have rendered the potential for a CSF leak a minor consideration in the selection of a surgical approach for the CVJ. Additionally, the panoramic view provided by the endoscope allows for superior visualization and detailed dissection, improving the precision and safety of the procedure.[10] Therefore, the remaining primary challenge in endoscopic odontoidectomy and ventral decompression of the CVJ lies in the anatomical constraints of the endonasal corridor. The exposure of the approach to the CVJ is restricted caudally by the hard palate and laterally by the tori and eustachian tubes.[11] These anatomical constraints underscore the need for modifications to enhance the caudal exposure without compromising the minimally invasive nature of the technique. This study introduces two innovative techniques, the contralateral nasofrontal trephination (CNT) and posterior palatectomy (PP), designed to overcome the constraints of the EEA in addressing challenges such as limited surgical exposure, difficulty in dural reconstruction, and reduced inferior reach during endonasal odontoidectomy and minimally invasive CVJ surgery. The study evaluates the anatomical access achieved with these techniques, comparing the limitations of exposure instrumentation of a standard EEA to those of an EEA combined with a CNT or a PP.

Materials and Methods

An endoscopic endonasal approach to the CVJ was performed on 15 adult human cadaveric specimens at the Anatomy Laboratory Toward Visuospatial Surgical Innovations in Otolaryngology and Neurosurgery (ALT-VISION) of the Wexner Medical Center of The Ohio State University. ALT-VISION and all researchers comply with university and government regulations regarding the use of human tissues. All specimens had been previously prepared, isolating the common carotid and vertebral arteries to cannulate and flush with warm water, thus clearing blood clots over three sessions. Subsequently, the vessels were injected with red and blue latex dye for the arterial and venous systems, respectively, to better visualize them during the dissections. All specimens were kept in a 70% alcohol solution throughout the procedure.

Visualization was provided with 0-degree and 30-degree rod-lens endoscopes of 4 mm diameter and 18 cm length (Karl Storz Endoscopy; Karl Storz, Tuttlingen, Germany) paired with a high-definition camera and video monitor. Video and digital images of the dissections were recorded during dissections using the AIDA recording system (Karl Storz Endoscopy; Karl Storz, Tuttlingen, Germany). Following the placement of five screws spanning the entire cranium, the specimens were scanned with a high-resolution multiplanar 1-mm cut computed tomography (CT). Standard endonasal instruments, along with a high-speed drill (Medtronic Corp; Jacksonville, FL), were used for the dissection. Digital Imaging and Communication in Medicine (DICOM) data were exported to a neuronavigation software (v. 1, GTx-Eyes II Approach Viewer, University Health Network, University of Toronto, Toronto, ON, Canada) to visualize the measurements of the endoscopic corridors recorded during the dissections, according to the validated method previously described by our group for the quantifications of various surgical approaches.[12] [13] [14] Quantitative radiological and anatomical measurements were performed based on the cadaveric surgical dissections.

Contralateral Nasofrontal Trephination (CNT) Approach

A 1.5-cm nasofrontal incision was performed between the nasal dorsum and the medial end of the eyebrow. The incision was carried down to bone, and the periosteum was elevated to reveal the meeting point between two suture lines separating three bones: the glabella of the frontal bone, the nasal bone, and the frontal process of the maxillary bone. Then, a trephine of 1.5 cm × 1.0 cm was drilled at this intersection, opening into the frontal recess ([Fig. 1]), following an inferomedial trajectory to avoid skull base injury as described. An inferomedial trajectory of the drill tip was confirmed to avoid injuring the skull base[15] ([Fig. 2]). A three-dimensional photogrammetry-generated model was rendered using RealityCapture software 1.5 (Epic Games) to illustrate the CNT approach trajectory toward the CVJ region (3D Model 1; https://sketchfab.com/3d-models/cnt-approach-corridor-to-cvj-018a2df55bbe426094511beb6974a5f8).

Fig. 1 The contralateral nasofrontal trephination (CNT) technique. The entry corridor of the CNT approach on the right side. (A) The incision line. (B) The bony landmarks after the elevation of the periosteum, including frontal bone (FB), nasal bone (NB), and frontal process of the maxillary sinus (FPmax). (C) The drilled trephination window. (D) Endoscopic endonasal view showing the entry of a suction tip from the nasofrontal trephination into the nasal cavity passing between the lamina papyracea and the middle turbinate. AEA, anterior ethmoidal artery; LP, lamina papyracea; MTR, middle turbinate remnant; SO, sphenoid ostium; ST, superior turbinate.

Fig. 2 Artistic illustrations showing the direction of the scope (A) and instrumentation (B) from the contralateral nasofrontal trephination (CNT) port toward the craniovertebral junction (CVJ) (palatal window drilled). Copyright of Mohammed Alwabili.

Endonasal Corridor

An EEA was performed by out-fracturing inferior turbinates, followed by anterior and posterior ethmoidectomies ipsilateral to the trephination. Anatomical landmarks around the CNT entry corridor were identified, including the anterior ethmoidal artery, the lamina papyracea, and the middle turbinate. A Draf II B procedure was then completed to enhance maneuverability and surgical freedom through the frontal recess (a Draf II A was sufficient to allow instrument access). This was followed by a posterior septectomy and removal of the sphenoid rostrum. The floor of the sphenoid sinus was drilled posteriorly to be flush with the clival recess, and anatomical landmarks, including foramina lacera, fossae of Rosenmüller, and eustachian tubes tori, were identified and preserved to serve as the lateral limits of the initial dissection.

Dissection of the Lower Clivus and the Craniovertebral Junction

The nasopharyngeal mucosa was incised in an inverted-U shape and reflected inferiorly, extending from the level of the sphenoid sinus floor down to the level of the soft palate. This allowed the exposure of the underlying pharyngobasilar fascia and the median raphe covering the prevertebral muscles. After the removal of the prevertebral fascia, the recti capitis anterior muscles were dissected, and the longi capitis muscles were lateralized. The anterior longitudinal ligament was exposed and dissected, revealing the underlying anterior atlantooccipital membrane. Key anatomical structures, including the foramen magnum arch, pharyngeal tubercle, occipital condyles, supracondylar grooves, and C1 vertebral arch, were exposed. The odontoid process was exposed with the attached apical and alar ligaments. Using the CNT, the odontoid process was drilled with the preservation of the C1 vertebral arch ([Fig. 3]). The most cranial portion of the odontoid process is identified behind the anterior arch of the atlas. Endoscopic visualization and instrumentation comparisons were made toward the C2, C3, and C4 vertebrae ([Fig. 4]). A three-dimensional photogrammetry-generated model was rendered using RealityCapture software 1.5 (Epic Games), showing the surgical dissection and visualization of the CVJ region using combined EEA and CNT approaches (3D Model 2; https://sketchfab.com/3d-models/craniovertebral-junction-reach-from-cnt-approach-472c78ee221b40539c51ffa64b836df0).

Fig. 3 An artistic illustration for the endoscopic visualization of the craniovertebral junction region. AOJ, atlanto-occipital junction; AT, anterior tubercle of C1; BA, basilar artery; C1 ant arch, C1 anterior arch; ET, eustachian tube; FL, foramen lacerum; FMA, foramen magnum arch; HC, hypoglossal canal; JT, jugular tubercle; OC, occipital condyle; Od, odontoid; PC ICA, paraclival internal carotid artery; PFD, posterior fossa dura; SAF, superior articular facet; SPF, salpingopharyngeal fold; TLA, transverse ligament of the atlas; TT, torus tubarius. Copyright of Mohammed Alwabili.

Fig. 4 Dissection of the craniovertebral junction (CVJ). (A) The clival recess after posterior septectomy, removal of the sphenoid rostrum, and drilling of the sphenoid floor. (B) Exposure of the lower clivus and the median raphe after dissection of the posterior pharyngeal mucosa. (C) Endoscopic 0-degree visualization of the CVJ, odontoid process, and alar and apical ligaments through the contralateral nasofrontal trephination (CNT) port after dissection of the prevertebral muscles. (D, E) Illustrations showing difference in views between the nose and CNT port using a 0-degree scope at the same point of the dissection. (D) Endoscopic endonasal 0-degree visualization of the CVJ. (E) Endoscopic CNT port 0-degree visualization of the CVJ. 6 CN, 6th cranial nerve; Alar L., alar ligament; AOJ, atlanto-occipital junction; Apical L., apical ligament; BA, basilar artery; C1 ant arch, C1 anterior arch; CP, carotid protuberance; CR, clival recess; ET, eustachian tube; FL, foramen lacerum; FMA, foramen magnum arch; HC, hypoglossal canal; IPS, inferior petrosal sinus; JT, jugular tubercle; LCM, longus capitis muscle; LPT, lateral pharyngeal tubercle; LR, lateral recess of the sphenoid sinus; MR, median raphe; NP, nasopharynx; OC, occipital condyle; Od, odontoid; PC ICA, paraclival internal carotid artery; PFD, posterior fossa dura; PT, pharyngeal tubercle; PWMS, posterior wall of the maxillary sinus; RCA, rectus capitis anterior; RF; Rosenmuller fossa; SAF, superior articular facet; SCG, supracondylar groove; SP, soft palate; SPF, salpingopharyngeal fold; TLA, transverse ligament of the atlas; TT, torus tubarius; V2, maxillary division of the trigeminal nerve; VN, vidian nerve.

Posterior Palatectomy (PP) Approach

This technique began with the elevation of a posteriorly based nasal floor mucosal flap, which involves three incisions, one horizontal incision at the level of the transverse palatine suture near the conchal crest and two vertical incisions separating the flap from the lateral nasal wall and septal mucosa. The flap was then reflected posteriorly, exposing the transverse palatine suture between the horizontal plate of the palatine bone posteriorly and the palatine process of the maxillary bone anteriorly ([Fig. 5A]).

Fig. 5 Posterior palatectomy approach. (A) Elevation of a posteriorly based nasal floor flap and exposure of the horizontal plate of the palatine bone; the three incision lines are highlighted in green. (B) The removal of the posterior nasal spine. (C) An artistic illustration showing the quadrangular bony window removed from the horizontal plate of the palatine bone. Copyright of Mohammed Alwabili. CC, conchal crest; ET, eustachian tube; HPP, horizontal plate of the palatine bone; NP, nasopharynx; PNS, posterior nasal spine; PWMS, posterior wall of the maxillary sinus; S, septum; SR, sphenoid recess; TPS, transverse palatine suture.

Subsequently, the horizontal plate of the palatine bone was carefully thinned using a high-speed drill until a delicate bony shell remained. This created a quadrangular bony window, leaving approximately half a centimeter of bone intact on both sides and continuous with the lateral nasal wall to safeguard the greater and lesser palatine foramina along with their associated artery and nerve. The thin bony shell was subsequently removed, including the posterior nasal spine, while preserving the underlying periosteum and palatal muscles. This technique allowed for preserving the underlying periosteum and palatal muscles. The mucosal floor flap could then be repositioned seamlessly ([Fig. 5]; [Video 1]). A three-dimensional photogrammetry-generated model was rendered using RealityCapture software 1.5 (Epic Games), illustrating the PP approach and the quadrangular bony window created (3D Model 3; https://sketchfab.com/3d-models/cvj-view-posterior-palatectomy-218a60bad54643e999ea51241908269a).

Video 1 This video describes the contralateral nasofrontal trephination, and the posterior palatectomy techniques as two promising approaches to expand the access to the craniovertebral junction inferiorly.

The EEA was performed first, followed by CNT, with the PP conducted last to avoid potential measurement bias associated with palate drilling.

Quantitative Analysis

The following parameters were studied for the EEA-only, and for the PP and CNT as complementary approaches to the EEA.

(1) Area of surface exposure and volume of surgical freedom: Studied on 10 cadavers.

Rendering of the target area was obtained from the CT scans of all specimens using ITK-SNAP software (v. 4.0.2). The study focused on the paramedian region, delimited superiorly by an axial plane passing at the level of the superior border of the C1 arch, while inferiorly the limit was represented by an axial plane at the level of the inferior margin of C4. The lateral borders were limited by a sagittal plane that passed through the most medial limit of the lateral masses of the first cervical vertebrae. Therefore, four different regions were identified, defined as the anterior surface of C1, the anterior surface of C2, the anterior surface of C3, and the anterior surface of C4. Contouring the desired region in each consecutive CT axial slice, each surgical volume was intersected with the target areas drawn in GTx-Eyes II Approach Viewer to obtain the value ([Fig. 6A]).

Fig. 6 (A) A three-dimensional rendering of the first four cervical vertebrae drawn over the CT scan using ITK-SNAP software. The paramedian region target was demarcated in the craniocaudal direction by an axial plane passing at the level of the superior border of the atlas, while caudally the limit was the inferior margin of the C4 body. The lateral borders were represented by a sagittal plane that passes through the most medial limit of the lateral masses. The paramedian region of the C1 arch is in red, the paramedian region of the C2 body is in yellow, the paramedian region of the C3 body is in sky blue, the paramedian region of the C4 body is in orange, the lateral mass of C1 is in green, lateral mass of C2 is in blue, lateral mass of C3 is in pink, lateral mass of C3 is in purple. (B–D) Illustrations showing the volume of surgical freedom for the three surgical approaches in the x-y-z plane and three-dimensional reconstruction using the Approach Viewer software (University Health Network, University of Toronto, Toronto, ON, Canada) to expose the first cervical vertebra from different endoscopic corridors. (B) Endoscopic endonasal approach (EEA; in red). (C) Endoscopic endonasal approach with posterior palatectomy (PP; in green). (D) Contralateral nasofrontal trephination (CNT; in blue).

The volume of surgical freedom was defined as the maximal available working volume with respect to a specific surgical corridor and target structure. The key structures comprised four midline points from superior to inferior: the odontoid process, C1 arch, body of C2, body of C3, and body of C4 vertebrae, respectively. To achieve this, GTx-Eyes II Approach Viewer (v. 1, GTx-Eyes II Approach Viewer, University Health Network, University of Toronto, Toronto, ON, Canada) was used to visualize volumes and deep areas of each approach as a surgical truncated pyramid, as previously defined by Andaluz et al.[16] The truncated pyramid was based at the nose for the EEA and EEA + PP and at the frontal trephination window for EEA + CNT ([Fig. 6B–D]).

(2) Reach and angles around the CVJ: Measured on 15 cadavers using the image guidance system.

The distance reached below the odontoid for each approach was calculated ([Fig. 7A]), and the angles around the CVJ related to the entry point of each approach were measured, including:

• The naso-palatine angle, which was taken as a reference sagittal angle for the EEA, was defined as the angle between the defined nasoaxial line[17] and the hard palate line meeting at the posterior nasal spine point ([Fig. 7B]).

• The naso-maxillary angle, which was taken as a reference sagittal angle for the EEA + PP approach, was defined as the angle between the nasoaxial line and the hard palate line meeting at the level of the transverse palatine suture ([Fig. 7C]).

• The fronto-palatine angle, which was taken as a reference sagittal angle for the CNT, was defined as the angle between the trajectory of a line drawn from the CNT entry and the hard palate line (fronto-palatine line) meeting at the posterior nasal spine ([Fig. 7D]).

Fig. 7 Reach and angles around the craniovertebral junction (CVJ). (A) The distance below the odontoid process that was reached for each approach; endoscopic endonasal in sky blue, posterior palatectomy in orange, and contralateral nasofrontal trephination in green. (B) The naso-palatine angle. (C) The naso-maxillary angle. (D) The fronto-palatine angle.

Statistical Analysis

The distribution of continuous variables (volume of surgical freedom, surface area, entry point angle, and distance below odontoid) was represented using boxplots. The Shapiro-Wilk test was used to assess data normality distribution, and Levene's test was applied to confirm the homogeneity of variances. One-way analysis of variance (ANOVA) was performed to compare the means between the three surgical approaches (EEA, EEA + PP, and EEA + CNT), followed by Tukey's HSD (honestly significant difference) post hoc analysis for multiple comparisons. All statistical analyses were performed using JASP statistical software (Version 0.19.1.0).

Results

Area of Exposure

The mean areas of surface exposure were 69.78 ± 9.87 cm² (EEA), 86.26 ± 8.40 cm² (EEA + PP), and 107.04 ± 17.07 cm² (EEA + CNT). A one-way ANOVA was conducted to compare the effects of the three approaches (EEA, EEA + PP, and EEA + CNT) on the surface area. ANOVA revealed significant differences among the approaches (p < 0.001), and Tukey's HSD post-hoc comparisons revealed significant differences between EEA and EEA + CNT (p < 0.001), EEA + PP and EEA + CNT (p = 0.002), and EEA and EEA + PP (p = 0.016) ([Fig. 8A]).

Fig. 8 Box-and-whisker plots showing the distribution of the area of surface exposure (A), the volume of surgical freedom (B), entry point angles (C), and distance reached below the odontoid process (D), stratified by each surgical approach. CNT, contralateral nasofrontal trephination; EEA, endoscopic endonasal approach; PP, posterior palatectomy.

Volume of Surgical Freedom

For the volume of surgical freedom, the means were 26.13 ± 6.19 cm³ for EEA, 34.14 ± 6.23 cm³ for EEA + PP, and 60.21 ± 3.82 cm³ for EEA + CNT with significant differences among groups (p < 0.001) confirmed by ANOVA. Tukey's HSD post-hoc analysis comparisons showed significant differences for pairwise comparisons between EEA and EEA + CNT (p < 0.001), EEA + PP and EEA + CNT (p < 0.001), and EEA and EEA + PP (p = 0.009) ([Fig. 8B]).

Entry Point Angle

The entry point angles averaged 16.6 ± 1.13 degrees for naso-palatine, 21.4 ± 2.01 degrees for naso-maxillary, and 50.1 ± 3.10 degrees for fronto-palatine approaches with post-hoc comparisons showing significant differences among and between all groups (p < 0.0001) ([Fig. 8C]).

Reach Below the Odontoid Process

The mean distances reached below the odontoid process were 0.9 ± 0.11 cm (EEA), 2.17 ± 0.3 cm (PP), and 6.35 ± 0.8 cm (CNT). Post-hoc analysis revealed significant differences between all the approaches (p < 0.0001) ([Fig. 8D]).

Discussion

Anterior approaches for decompressing the CVJ can be broadly classified into three main techniques: transoral, transcervical, and transnasal.[6] Historically, the transoral and transcervical routes implied an open surgical procedure with direct visualization; however, modern advancements now incorporate endoscopic assistance to improve outcomes.[18] [19] [20] We propose that the endonasal approach offers untapped potential for further development of CVJ surgery, historically considered a “no man's land.”

Current literature demonstrates that although both transoral and transnasal approaches provide adequate exposure at the C1 level, the endonasal approach is less effective in lower regions.[21] The feasibility of a transnasal endoscopic odontoidectomy relies on the preoperative assessment of the radiological “nasoaxial line” to gauge the maximal inferior extent of the surgical corridor.[17] However, recent studies doubt these predictive measures and suggest that hard palate length is the only reliable predictor.[22] To overcome the lower reach limitation, we evaluated two novel adjunct approaches innovated by our research group: the CNT and the PP.[15] [23] The nasofrontal trephination was preferred to be performed on the contralateral side of the long axis of the lesion, as this will provide the most direct visualization and instrumentation. Overall, the two techniques added to the caudal exposure and reach of the core endonasal surgical corridor.[24] [25] [26]

In this study, the standard EEA exposure extended to the C1–C2 junction level, which is consistent with the literature.[21] In comparison, the CNT approach extended the caudal reach to the upper half of the C4 vertebra, while a PP extended the caudal reach to the C2–C3 junction, both surpassing the nasoaxial line limitation. Quantitatively, the mean distance reached below the odontoid for both the CNT and the PP was statistically significant compared with the EEA alone (p < 0.0001). Reaching these more caudal levels may allow access to pathologies located at or below the C2 level, which can be critical for adequate decompression in select patients, particularly for treating conditions such as basilar invagination, rheumatoid pannus, and neoplasms that involve the lower CVJ and upper cervical spine.

The CNT approach offers several distinct advantages. First, it enables complete access to the odontoid process till its base while preserving the C1 arch and the transverse ligament of the atlas through straight instrumentation. This preservation of atlantoaxial joint stability may potentially eliminate the need for postoperative cervical spine fixation. However, this requires further research and clinical correlation.[27] Additionally, the CNT approach offers excellent postoperative cosmetic outcomes, as its incision can be discreetly hidden within the medial part of the eyebrow.[28] [29] Although curved instruments can enhance the inferior reach of EEA, similar benefits apply to the PP and CNT approaches, albeit with inherent limitations such as reduced maneuverability and blind spots around the instrument tip. Furthermore, in cases of extensive lesions with lateral extension, particularly those extending to the infrapetrous region, the CNT's superior sagittal angle of attack, resulting from its higher entry point, eliminates the need for eustachian tube mobilization by providing direct access behind it, ensuring an unobstructed surgical corridor.[30] The approach's entry point at the frontal recess provides an additional safety advantage, positioning below the skull base and avoiding olfactory fiber injury. The enhanced fronto-palatine angle achieved with a CNT offers superior directional access to the CVJ compared with standard EEA and EEA + PP. This steeper trajectory allows for improved visualization and instrumentation.[17]

The area of deep exposure reflects the accessible surgical surface centered on the target anatomy, while the volume of surgical freedom represents the maneuverability within the corridor for optimal use of surgical instruments and effective visualization. Both CNT and PP techniques demonstrated significant improvements in the area of deep exposure and volume of surgical freedom compared with the standard EEA, with the CNT showing particular advantages for extensive surgical manipulation.

This improvement reduces instrument conflict by creating a new ergonomic axis and, thus, may be clinically significant. A notable innovation of the CNT is its creation of a secondary instrumentation axis, effectively minimizing instrument conflict “fencing effect,” where instruments conflict within a single axis, through a dual-port configuration. This setup enables simultaneous operation by multiple surgeons, potentially enhancing procedural efficiency.[31] [32] [33] Additionally, we were able to introduce two instruments through the CNT port. However, the trade-off involved some reduction in maneuverability due to the rigid bony boundaries of the access port. Future studies should explore refining nasofrontal trephination ergonomics to optimize instrument flexibility without compromising the benefits of expanded access. Our cadaveric experience suggests that the CNT approach is particularly advantageous for lesions with significant caudal extensions, while the PP presents a viable alternative for lesions confined within the C2–C3 caudal limit, especially in cases where CNT may be less feasible or when additional external incisions are undesirable.

Regarding the PP technique, the maximum safe drilling window was achieved by targeting the horizontal plate of the palatine bone. However, removing only the posterior nasal spine and a small surrounding segment of bone can also effectively enhance paramedian inferior access to the CVJ. It is important to note that only the bony component should be removed while preserving the underlying periosteum, as overly aggressive resection may lead to complications such as velopharyngeal insufficiency with voice changes and nasal regurgitation or the development of a palatal fistula. The lateral extension of palatine bone drilling was performed to improve surgical maneuverability and to demonstrate the maximum bone removal possible when addressing lesions that extend more laterally. Also, the PP, which includes raising the posteriorly based nasal floor mucosal flap,[34] maintains the traditional endonasal axis while modestly improving surgical exposure.

Conclusion

This study highlights the advantages of the CNT and PP approaches as adjuncts to the EEA for CVJ access. Both the techniques contributed to the caudal exposure and instrument reach of a basic EEA to the CVJ. The CNT approach offered the widest exposure, largest surgical freedom, and best caudal reach. These findings suggest that incorporating CNT or PP can expand the EEA's versatility, potentially improving outcomes for CVJ pathologies. Further clinical validation is needed to confirm these benefits. This cadaveric study carries some implied limitations as the observed tissue pliability may not fully replicate what occurs in living patients, and the absence of pathological lesions limits the ability to model the anatomic distortions that may arise in clinical scenarios.

Conflict of Interest

None declared.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

This article was selected to receive the Rhoton Award at the 34th North American Skull Base Society Conference in New Orleans, Louisiana, USA, 2025.

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Publikationsverlauf

Eingereicht: 16. Januar 2025

Angenommen: 21. März 2025

Accepted Manuscript online:
25. März 2025

Artikel online veröffentlicht:
12. Mai 2025