An Anatomically-Based Endoscopic Endonasal Model to Navigate the Anterior Ventral Skull Base

Journal Pre-proof Proposal of an Anatomically-Based Endoscopic Endonasal Model to Navigate the Anterior Skull Base Using the Orbitosellar Line (OSL), Critical Oblique Foramen Line (COFL), and Paramedian Anterior Line (PAL) as Coordinates Laila Perez de San Roman Mena, MD, Alejandro Monroy-Sosa, MD, Srikant S. Chakravarthi, MD, MSc, Lior Gonen, MD, Austin Epping, BSc, Sammy Khalili, MD, William Smithee, BSc, Juanita M. Celix, MD, MPH, Bhavani Kura, MD, Jonathan Jennings, MD, Richard A. Rovin, MD, Melanie B. Fukui, MD, Amin B. Kassam, MD PII:

S1878-8750(19)32710-X

DOI:

https://doi.org/10.1016/j.wneu.2019.10.091

Reference:

WNEU 13562

To appear in:

World Neurosurgery

Received Date: 6 May 2019 Revised Date:

14 October 2019

Accepted Date: 15 October 2019

Please cite this article as: Perez de San Roman Mena L, Monroy-Sosa A, Chakravarthi SS, Gonen L, Epping A, Khalili S, Smithee W, Celix JM, Kura B, Jennings J, Rovin RA, Fukui MB, Kassam AB, Proposal of an Anatomically-Based Endoscopic Endonasal Model to Navigate the Anterior Skull Base Using the Orbitosellar Line (OSL), Critical Oblique Foramen Line (COFL), and Paramedian Anterior Line (PAL) as Coordinates, World Neurosurgery (2019), doi: https://doi.org/10.1016/j.wneu.2019.10.091. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.

Title: Proposal of an Anatomically-Based Endoscopic Endonasal Model to Navigate the Anterior Skull Base Using the Orbitosellar Line (OSL), Critical Oblique Foramen Line (COFL), and Paramedian Anterior Line (PAL) as Coordinates Authors: Laila Perez de San Roman Mena1 MD, Alejandro Monroy-Sosa1 MD, Srikant S. Chakravarthi1 MD, MSc, Lior Gonen2 MD, Austin Epping1 BSc, Sammy Khalili1 MD, William Smithee3 BSc, Juanita M. Celix1 MD, MPH, Bhavani Kura1 MD, Jonathan Jennings MD, Richard A. Rovin1 MD, Melanie B. Fukui1 MD, Amin B. Kassam1 MD 1

Aurora Neuroscience Innovation Institute, Aurora St. Luke’s Medical Center, Milwaukee, WI. Shaare Zedek Medical Center, Jerusalem, Isreal 3 School of Medicine, University of Texas Medical Branch, Galveston, TX 2

Corresponding Author: Amin B. Kassam, MD Aurora St. Luke’s Medical Center, Suite 680 2801 West Kinnickinnic River Parkway, Milwaukee, WI 53215 E-mail: [email protected] Disclosure: Amin Kassam reports involvement in Synaptive Medical (consultant), KLS Martin (consultant), Medtronic (advisory board), and founder and CEO of Neeka Health, LLC. Key Words: orbito-sellar line (OSL); critical oblique foramen line (COFL); paramedial anterior line (PAL); endoscopic endonasal approach; sellar and parasellar; skull base Short Title: Anatomically-based Model for the Ventral Skull Base Disclosure of Funding: None Industry Affiliations: Amin Kassam reports involvement as a consultant to Synaptive Medical, KLS Martin Medical, Medtronic Advisory Board, and founder and CEO of Neeka Health, LLC. Acknowledgments: This research is supported by an award to the Aurora Research Institute by the Vince Lombardi Cancer Foundation. We would like to thank Nico Corporation, Carl Zeiss, Stryker Medical, and Karl Storz for their donations that made our research possible in the Neuroanatomy Laboratory. Patient consent: Consent was obtained from all patients.

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BACKGROUND: Endoscopic endonasal approaches to access the sellar and parasellar regions are challenging in the face of anatomical variations or pathological conditions. OBJECTIVE: Propose an anatomically-based model including the orbito-sellar line (OSL), critical oblique foramen line (COFL), and paramedial anterior line (PAL) facilitating safe, superficial-todeep dissection triangulating upon the medial opticocarotid recess (MOCR). METHODS: Five cadaveric heads were dissected to systematically expose the OSL, COFL, PAL illustrated with image-guidance. Application of the coordinate system and 6-step dissection sequence is described as well. RESULTS: The coordinate system consists of: 1) OSL, connecting a) anterior orbital point (AOP), junction of the anterior buttress of the middle turbinate with Agger nasi region, located 34.3 +/- 0.9 mm above the intersection of the vertical plane of the lacrimal crest and the orthogonal plane of the maxilloethmoidal suture, b) posterior orbital point (POP), junction of the optic canal (OC) with the lamina papyracea, located 4 +/- 0.7 mm below the posterior ethmoidal artery (PEA), and c) MOCR ; 2) COFL (15 +/- 2.8 mm) connecting the palatovaginal canal, vidian canal (VC) and foramen rotundum and 3) PAL (39 +/- 0.06 mm) connecting the VC with the posterior ethmoidal artery. CONCLUSIONS: OSL, COFL, and PAL form an anatomically-based model for the systematic exposure when accessing the parasellar and sellar region. Preliminary anatomical data suggests that this model may be of value when normal anatomy is distorted by pathology or anatomic variations. Short Title: Anatomically-based Model for the Ventral Skull Base Key Words: orbito-sellar line (OSL); critical oblique foramen line (COFL); paramedial anterior line (PAL); endoscopic endonasal approach (EEA); sellar and parasellar; skull base Abbreviations: Endoscopic endonasal approach (EEA); Internal carotid artery (ICA); Computerassisted neuronavigation (CAN); optic canal (OC); orbito-sellar line (OSL); medial opticocarotid recess (MOCR); critical oblique foramen line (COFL); palatovaginal canal (PVC); vidian canal (VC); foramen rotundum (FR); paramedian anterior line (PAL); posterior ethmoidal artery (PEA); lamina papyracea (LP); anterior orbital point (AOP); middle turbinate (MT); superior turbinate (ST); nasoseptal flap (NSF); sphenopalatine foramen (SPF); posterior orbital point (POP); lateral opticocarotid recess (LOCR); extraocular muscles (EOMs); superior oblique muscle (SOM); medial rectus muscle (MRM); inferior rectus muscle (IRM).

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INTRODUCTION:

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The deep, narrow corridor to the sellar and parasellar regions, with congested anatomy of

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vital neurovascular structures, presents an inherent challenge to safe access via endoscopic

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endonasal approaches (EEA) 1-14. Access becomes increasingly difficult with: 1) anatomical

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variations, such as Onodi cells, internal carotid artery (ICA) canal dehiscence, poor pneumatization

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and 2) pathological distortion of anatomy.

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Computer-assisted neuronavigation (CAN) technology has advanced progress towards

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solutions 15,16. Barriers to CAN, include availability, cost, and personnel, that have precluded global

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utilization. Application of CAN, however, remains reliant on understanding, and colocalization in

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real-time, of critical anatomic landmarks that provide guiding fiducials.

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While several direct individual anatomic landmarks underpin a path to the pituitary fossa,

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they are variable and often identified late in dissection, providing an “inside-out,” deep-to-

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superficial, validation of the trajectory. We sought to construct an anatomically-based system of

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fiducial landmarks to create a superficial-to-deep, “outside-in,” trajectory to sequentially locate

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vital parasellar and sellar structures (optic canal (OC), paraclinoidal ICA). This bilateral

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framework triangulates to converge upon the pituitary fossa.

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We propose a framework consisting of three lines which constitute an anatomically-based

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model to navigate the ventral skull base: 1) orbito-sellar line (OSL): connecting the orbit and sella

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turcica and guides sequential exposure of the orbit, OC, paraclinoid carotid and medial

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opticocarotid recess (MOCR); 2) critical oblique foramen line (COFL): connecting the

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palatovaginal canal (PVC), vidian canal (VC) and foramen rotundum (FR) from inferomedial to

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superolateral; and 3) the paramedian anterior line (PAL): vertically connecting the VC to the lateral

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opticocarotid recess (LOCR) and the posterior ethmoidal artery (PEA) at the lamina papyracea (LP)

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junction; and(Figure 1).

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Objectives: To describe a preliminary anatomically-based model to navigate the sellar and

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parasellar regions using cadaveric dissections.

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PATIENTS AND METHODS

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Anatomic dissections (Figure 2):

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Five formalin-preserved and injected cadaveric heads were prepared for dissection.

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Endonasal anatomic dissections were performed using rod lens endoscopes (Karl Storz, 4 mm, 18

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cm, Hopkins II, 0º and 45º, Karl Storz, Tuttlingen, Germany) attached to a high-definition camera

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and a digital video recorder system. Heads were fixed with a Mayfield head clamp in a supine,

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neutral position. Nasal-stage was completed in standard EEA fashion. The anterior orbital point

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(AOP), which we define as the junction of the anterior buttress of the middle turbinate (MT) and the

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Agger nasi region, was identified as the first landmark. The inferior one-third of the MT was

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resected (or mobilized); the buttress of the MT was preserved and used to locate the AOP.

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Dissection continued with raising of the pedicled nasoseptal flap (NSF). The sphenopalatine

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foramen (SPF) was unroofed, exposing the medial pterygoid “wedge.” The rostrum of the sphenoid

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was removed en-bloc through V-osteotomies, along both PVCs. Following the PVC obliquely from

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medial to lateral, VC was exposed as the second key anatomic landmark. Next, the maxilla and the

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LP were addressed. Posterior ethmoidal cells were completely removed exposing the orbital apex,

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allowing identification of the posterior orbital point (POP), which we define as the junction of the

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OC with the LP, as the third key landmark. The posterior ethmoidectomy was limited to the margin

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of the posterior ethmoidal artery to avoid anosmia. After these landmarks were identified, the

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deeper sphenoid-phase was initiated, with bilateral sphenoidotomies and sphenoid floor drilling,

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providing a wide view of the sphenoid sinus. Sphenoid septations were reduced, exposing the

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deeper skull base landmarks: the OC, paraclinoid prominence, and lateral opticocarotid recess

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(LOCR). Finally, the OC was followed medially to locate the fourth, and final, critical landmark:

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the MOCR and junction of the lateral margin of the tubercular strut. We have defined the most

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lateral extension of the Tuberculum as it transitions into the MOCR as the “lateral Tubercular Strut”

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this represents a vital landmark in locating the MOCR, Optic nerve and Paracliniodal ICA. Once

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the MOCR was located, the bone over the medial cavernous carotid segment and sellar interface

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was eggshelled and removed, culminating in removal of the MOCR itself. Each of the regions

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within the anteromedial and anterolateral skull base were exposed and analyzed. Measurements

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were recorded and further processed using the ImageJ software (NIH, Bethesda, Maryland, USA).

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RESULTS

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We identified three points which, when connected, produced a trajectory. These points are as

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follows (Figure 2 & 3):

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A. Anterior orbital point (AOP): a) Soft-tissue: the most anterior point of intersection (anterior buttress) of the MT with the Agger nasi region, reflected laterally on the LP.

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b) Osseous: after soft-tissue removal, this point is 34.3 +/- 0.9 mm above the

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intersection of the vertical plane of the lacrimal crest and the orthogonal plane of

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the maxilloethmoidal suture, which we defined as the union between the lamina

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papyracea of the ethmoid bone and the angle between the roof and medial wall of

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the maxillary sinus. This union can be seen in pterygopalatine and/or orbital

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approaches, as well as serving as a useful landmark, from superficial to deep, to

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locate the LOCR.

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B. Posterior orbital point (POP):

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a) Soft-tissue: the posterior MT buttress correlates to the attachment of the

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ethmoidal crest of the palatine bone, anterior to the SPF. VC is immediately

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superolateral to the PVC.

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b) Osseous: a vertical line from VC passing across the LOCR to the junction of the

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PEA with the LP, directly extends through the junction of the OC and LP. This

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latter point marks the POP, 4 +/- 0.7 mm below the PEA. We have termed this

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the paramedian anterior line (Figure 1). The POP is intersection of the OC with

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LP. This represents the point of the OC immediately superolateral to LOCR and

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overlying the annulus of Zinn.

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C. MOCR: a) A teardrop-shaped osseous depression at the medial intersection of the

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paraclinoid ICA canal and the OC 17. A good surrogate for the MOCR is the

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lateral extension of the tubercular strut.

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We define the OSL as a line from anterolateral to posteromedial and from superior to inferior along

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the AOP, POP, and MOCR. The trajectory traverses the lamina papyracea (LP) from distal

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(superior, anterior, lateral) to proximal (inferior, posterior, medial), represented by the OC. The LP

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has a rectangular shape, framed by the fovea ethmoidalis superiorly, maxilloethmoidal suture and

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maxillary sinus roof inferiorly, lacrimal crest anteriorly, and the sphenoid sinus lateral margin

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posteromedially. A line initiated at the AOP, just behind lacrimal crest (LC), where the anterior

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buttress of the MT meets the Agger nasi region, is an early landmark and is projected laterally over

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the LP. The OSL continues posteriorly towards the posterosuperior corner of the rectangle,

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correlating with the annulus of Zinn at the orbital apex, where the LP meets the OC (POP) and then

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extends to the sellar region, extending over the OC to the MOCR. The MOCR is a key landmark for

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endoscopic approaches to the sellar and suprasellar regions 17. Removal of bone overlying the

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MOCR allows identification of the optic nerve (ON) and paraclinoid ICA18. The maxilloethmoidal

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suture is an adjunct to the OSL. Its thick strut of bone forms the inferior border of the medial orbital

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wall and provides support to the orbit (Figure 1). Early cadaveric dissections demonstrated that a

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line projected posteriorly from the maxilloethmoidal suture lead to the LOCR, providing a

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potentially useful reference line. This line may be important, especially under adverse

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circumstances (ie., poor pneumatization or distorted anatomy remodeled by tumor) because it

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provides a triangulation point in order to locate the POP if this is not visible. POP will be located

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along the paramedian anterior line and above the LOCR which we can locate with the projection of

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the maxillo-ethmoidal suture. Finally, the PVC, VC, and FR are oriented obliquely19 (from medial

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to lateral and inferior to superior, respectively), within the inferior oblique border of the sphenoid

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bone (Figure 2D). Although this relationship has been previously described, for the purposes of

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this proposed model, we have termed this line the critical oblique foramen line (COFL).

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Dissection of anatomical specimens

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EEA was performed in 5 specimens, allowing examination of 10 OSLs, COFLs and PALs.

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1. The OSL was divided into two segments that were analyzed individually (Figure 3 and 4). The

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AOP, POP, and MOCR were used to define the segments:

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• LP segment: extends from the AOP to the POP, at the orbital apex.

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• ON segment: encompasses the distance from the POP to the lateral-most aspect of the MOCR, at

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the lateral margin of the tubercular strut.

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Measurements along the two segments were: (Table 1): 28.2 +/- 0.05 (LP segment) and 10.3 +/-

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0.03 mm (OC segment). OSL was 37.7 +/- 0.02 mm in total. Neuronavigation was used to identify

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the AOP, POP, and MOCR (Figure 5). To provide cross-correlation with the OSL, a trans-LP

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approach was performed; the periorbita was resected and the orbital fat was removed exposing the

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extraocular muscles (EOMs). Further dissection exposed the superior oblique muscle (SOM),

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medial rectus muscle (MRM) and inferior rectus muscle (IRM). This provided a direct correlation

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between the OSL with the EOMs and the intraconal compartment. The OSL was oriented along

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the long axis of the MRM in every specimen.

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2. Measurements along COFL were also performed:

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Distance from the lateral margin of PVC to the medial margin of VC = 4.1 +/- 1.1 mm

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Distance from the lateral margin of VC to the medial margin of FR = 5.3 +/- 1.2 mm

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•

Total length of COFL (from medial margin of PVC to lateral margin of FR) = 15 +/- 2.8

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mm 3. PAL: distance from VC to PEA (at the LP junction) = 39 +/- 0.06 mm

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Recommended Surgical Sequence based on the Anatomically-based Model:

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Our recommended surgical sequence consists of 6 distinct steps: Step 1) the MT anterior

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buttress is identified and the AOP of the OSL is located. Step 2) the sphenoid ostium is located and

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the PVC identified; the vomer is resected and followed to the VC after identification of SPF with

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dissection superolaterally, as needed, along the COFL. Step 3) extending from superficial to deep,

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the OSL is followed to the POP (3a) and then we travel vertically along the PAL (3b) to triangulate

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on the POP and LOCR. In cases with distorted anatomy, the maxilloethmoidal suture can be traced

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posteriorly to identify the LOCR. Step 4) the POP and the LOCR are located, triangulation then is

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carried out along the OC from the POP to the MOCR. Step 5) travels from the LOCR along the

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paraclinoidal ICA to converge on the MOCR/lateral margin of the tubercular strut. Step 6) Finally,

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after all landmarks have been established, we eggshell the bone overlying the

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paracavernous/paraclinoidal ICA along the lateral boundary of the sella. This culminates in

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removing the MOCR to provide control of the ICA and ON. We use this sequence systematically

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and find it to be safe and efficient, particularly in cases of a non-pneumatized lateral sphenoid

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recess.

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DISCUSSION EEA for access of the sellar and parasellar regions is critically dependent on the relative

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position of anatomical structures. Anatomical variations, atypical pneumatization, and distorting

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pathology create surgical challenges, especially in anticipating critical deep-seated neurovascular

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structures, such as the ICA or ON. Conventional direct access through the sphenoid sinus begins

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deep and medial and relies on identifying deep structures early, made problematic by anatomic

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variations and distortion.

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Several intrasphenoidal structures (LOCR, MOCR, clinoidal carotid prominence, OC, etc.),

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have been used as landmarks in accessing the sellar and parasellar regions. While we have

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previously detailed these vital landmarks they may be difficult to identify in cases with complex

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sphenoid septa (9%), poor pneumatization (0.5-15%),20 or when anatomy is distorted by pathology.

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Anatomic variations, especially an Onodi cell, present in 11.4% 20,21,22, may increase the risk of ON

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injury. Similarly, dehiscence of the ICA can lead to catastrophic complication.

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In contrast to the approach of identifying deep structures early, we advocate a superficial-to-

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deep trajectory, using systematic dissection predicated on three anatomically-based lines.

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Anticipation of critical landmarks by identifying superficial surrogates may mitigate the risks of

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injury to deep, critical neurovascular structures, particularly when variant or pathologically

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distorted anatomy is present. We first described the OSL, a reliable anatomical guide, connecting

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the orbit to the sella turcica and serving as a guide in locating the orbit, OC, paraclinoid ICA, and

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MOCR.

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anterior cranial fossa (Figure 7). Two variations might be encountered: 1) a flat skull base in which

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the angle formed with the OSL is so acute that it is nearly non-existing; this scenario may hamper

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identification of the supraoptic recess leading to inadvertently entering the anterior cranial base, and

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2) a steeper anterior skull base which forms a wider angle with the OSL; this allows for

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better visualization of the supraoptic recess. This difference can be reliably identified on sagittal CT

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scan and may be of importance when addressing pathologies located in this region. The proposed 3-

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line model is particularly valuable in the first instance and may require undertaking a limited

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posterior ethomoidectomy based on the geometry of the skull base, we would advocate doing so if

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it is required to identify and control the critical anatomy.

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An important consideration when applying the OSL is to analyze its angle with the

Secondly, the COFL facilitates easy identification of these landmarks, to preserve them as

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reference points (e.g., VC to identify the petrous ICA), and subsequently the origin of a vertical line

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(PAL) to the POP. It is again important to note that COFL was previously described19 , however we

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believe this line, especially if followed from the palatovaginal canal to the vidial canal, is critical in

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directly locating and moving along the PAL vertically towards the LOCR. Two oblique lines

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(COFL and OSL) provide identification of anatomy in the superficial and deep planes respectively.

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Finally, with the addition of the vertical PAL, the entire ventral anteromedial and anterolateral skull

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base is encompassed. We would like to point out that while exposing the PVC and VC in our

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practice is routinely performed, exposure of the Foramen Rotundum is only pursued if lateral or

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middle fossa extension is needed. For the purposes of exposing the sellar and parasellar region,

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once the VC is located, the paraclival ICA can be effectively identified and followed rostrally by

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drawing a line from the VC to the LOCR representing the PAL.

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There has been significant debate over the past two decades with respect to the degree of

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exposure required for sellar, parasellar and expanded approaches. Since our initial descriptions of

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the EEAs we have been strong proponents of wide bilateral exposures both to facilitate bimanual

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dissection and clear identification and control of the vital anatomic structures 23,24. We believe that

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the primary reason we have had a limited number (three ICA injuries in over 1,500 EEA

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procedures) of ICA injuries in over two decades, is the wide exposure we routinely undertake,

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while this is beyond the scope of this manuscript and focus of an upcoming report, it is important to

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mention as we routinely have used this coordinate system over this time period.

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Having said that, we also appreciate that each individual surgeon may wish to tailor their

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exposures based on their individual preference and we would like not to be prescriptive. Instead,

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we offer a modular systematic approach noting the interplay of each of the key landmarks and detail

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their clinical applicability below:

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a) The Anterior Orbital Point (AOP): AOP based on our experience is an anterior landmark

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and does not necessarily need a posterior ethmoidectomy; in fact, it can be effectively

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identified by simply following the middle turbinate to the skull base and locating the lamina

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papyracea at the junction. Having said that, we however, do believe it is valuable to

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undertake a posterior ethmoidectomy when necessary to adequately expose the optic canals,

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tuberculum and planum based on the extent of the tumor and the morphology of the skull

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base. We advocate undertaking the needed exposure based on the geometry and anatomy

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and believe that a compromised limited exposure may be hazardous. This is particularly the

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situation when there is a flat skull base as noted above, and therefore, an important

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consideration when applying the OSL is to analyze its angle with the anterior cranial fossa

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(Figure 7).

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b) The Palatovaginal Canal and the Vidian Canal anatomically do not require a transpterygoid

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exposure to be identified. With respect to the PVC, this is routinely exposed within the

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vomer and is located medial to the pterygoid plate at the level of the previously described

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“medial pterygoid-wedge”.

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c) The Vidian canal is anatomically located at the lateral extension of the vomer as it meets the

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pterygoid. Exposing the Vidian does not, in our experience, require removing or exposing

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the pterygoid. The Vidian canal is a vital landmark, and has been extensively described

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since our original description over decade ago to locate the paraclival ICA on the way to the

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sellar ICA. We do routinely expose it for this purpose and again have not needed a

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transpteryoid approach to do so. Furthermore, for the exposure of the lateral recess of the

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sphenoid sinus, represented as that component superolateral to the pterygoid, cannot

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routinely be effectively achieved while still allowing for bimanual dissection without

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exposure of the Vidian canal. Therefore, we believe this is a critical landmark in the schema

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for all endoscopists to be aware of.

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d) The Foramen Rotundum is not usually exposed for routine cases; but rather, this is only needed for lateral and middle fossa extensions.

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Application of the 6-step sequence and the proposed 3-line model can be summarized in the

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beginning with identification of the Middle Turbinate to locate the AOP and then locate the vomer

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and PVC, following it to the VC. Once the Vidian canal is exposed, the lateral extension can then

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stop if not needed without exposing the FR. From the Vidian canal, a straight vertical line can now

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be drawn to the LOCR and this forms the PAL reliably allowing for the remainder of the sellar,

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parasellar exposure to occur without lateral extension and the Foramen Rotundum is only pursued if

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lateral or middle fossa extension is needed. For the purposes of exposing the sellar and parasellar

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region, once the VC is located, the paraclival ICA can be effectively identified and followed

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rostrally isolating the ICA and the Optic Nerve from inferior to superior to avoid injury particularly

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in the setting of a dehiscence.

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Although the model which we present here would be ideally suited for cases in which the

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nasal, paranasal and sphenoid anatomy is preserved, the inherent challenges of using anatomically-

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guided fiducial systems for navigation are subject to the effects of distortion by anatomic variants

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or pathology. This disadvantage, as we have noted previously, is also the case with traditional

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anatomic landmarks such as ICA protuberance, MOCR, and LOCR which are also subject to the

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same distortions based on pathology, as well as, due to inherent variations. Our intention is not to

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replace these traditional and deeper landmarks nor to replace the use of navigation; rather, in this

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paper we add another layer of more superficial landmarks to augment the deeper ones. We believe

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the more reliable landmarks that can be consistently applied, the greater the accuracy and safety if

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some become distorted. Our intention is that in using the combination of the superficial to locate the

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deeper and then coupled with neuronavigation, further enhances the safety of proceeding.

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Notably, In addition, if available, intraoperative neuronavigation may serve as an adjunct in

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identifying critical anatomic landmarks, but should be used with caution, especially in the presence

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of variations. We again emphasize that CAN should only be used with context and a complete

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understanding of the regional anatomic landmarks, particularly in the setting of anatomic variations

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and pathological distortions.

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Overall, the practicality of this proposed anatomical model may lie in the ability to identify

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superficial structures and develop a more organized and reproducible system to access deeper

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critical structures in the sellar/parasellar region; particularly, in utilizing three anatomically-based

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lines: OSL, COFL, and PAL. Based on our clinical experience we have routinely used this

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sequence and we advocate for a wide bilateral exposure, from lamina papyracea to lamina

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papyracea, including bilateral sphenoidotomies; we believe that such an exposure provides a larger

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visual field, and as such may facilitate localization of deeper structures (eg. Optic canal and

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paraclinoidal ICA) and mitigation of inherent/expected variations (eg. Onodi cell, ICA dehiscence,

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poor pneumatization, hyperostosis, and distorted anatomy due to pathology) by having anatomic

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control and bimanual dissection with unencumbered mobility to deal with unexpected

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complications, eg. hemorrhage, should they do occur.

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As such, additional utilization of this linear coordinate system can facilitate careful

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dissection from a superficial to deep perspective, by creating “outer” and “inner” reference points,

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connected to each other, in order to address the potential aforementioned issues. In this report we

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detail the anatomic basis and nuances of the coordinate system we have routinely used for over two

327

decades, however, it’s true generalizability and applicability for others will need to be established.

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In the final analysis we offer this as a mere suggestion, in a desire to share our experience with

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reader for their consideration and ultimately know the reader will determine the applicability based

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on personal and individual circumstances.

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LIMITATIONS

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There are several important limitations which are worth mentioning here. Our preliminary results

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are based on a limited set of data and is meant only to provide a potentially useful EEA model; as

11 335

such no definite conclusions, with respect efficacy and reproducibility, can be made. On the other

336

hand, the intention of creating the OSL, in particular, was in the event of distorted anatomy;

337

whether the model as a whole (including COFL and PAL) and the concomitant advised surgical

338

sequence is applicable in such cases, is the subject of a forthcoming study. Although, direct

339

applicability of cadaver dissections to in vivo human experience can be difficult due to distorted

340

superficial anatomy, especially in the context of bony landmarks (i.e. pterygoid canal,

341

sphenopalatine foramen) where extradural tumors can be completely hide and infiltrated by lesions

342

might reduce the applicability of our findings, therefore this model may not be applicable in the

343

case of severely and completely distorted anatomy and may preclude its utilization. Further and

344

larger anatomical and clinical studies will be needed to assess the efficacy of this model and

345

whether it can be reproducibly applied to a broader range of clinical scenarios. Therefore, many

346

efforts must be expended before these laboratory findings can be translated to better define a unique

347

paradigm model to navigate in a real surgical scenarios.

348 349 350

CONCLUSION The OSL, COFL, PAL represent an anatomically-based model that provides a line of

351

connection between the sellar and orbit regions, allowing early identification of critical structures.

352

The OSL extends from an anterolateral to posteromedial and superior to inferior direction along the

353

following three anatomical reference points, from superficial-to-deep: (1) AOP, (2) POP and 3)

354

MOCR. The OSL can provide a guide in gradually exposing the LP, OC, paraclinoidal ICA and

355

MOCR. Preliminary, hypothesis-generating data, suggests that OSL, COFL, and PAL, in

356

combination, can create a safe and reliable anatomically-based model to navigate the ventral

357

anteromedial and anterolateral skull base.

358 359 360 361 362 363 364 365 366 367

LEGENDS

TABLE 1. Measurements of the OSL and its segments, COFL and PAL. FIGURE 1. Surgical sequence. Starting by identifying the MT anterior buttress and locating the AOP of the OSL (arrow 1). Sphenoid ostium will be located next as well as the PVC; then, vomer will be resected and VC (arrow 2) identified right after locating the sphenopalatine foramen. The OSL is now followed to the POP (arrow 3a) and only then do we travel vertically along the PAL (arrow 3b) to triangulate on the POP. Once POP and LOCR are located, triangulation is carried out

12 368 369 370 371 372 373 374 375 376

along the OC towards the MOCR (arrow 4). Next travelling from the LOCR, along the paraclinoidal ICA to converge on the MOCR/lateral margin of the tubercular strut (arrow 5). Finally, once all landmarks have been established, eggshelling the bone overlying the paracavernous/paraclinoidal ICA along the lateral boundary of the sella will be performed. AOP (anterior orbital point) COFL (Critical Oblique Foramina Line); ICA (Internal Carotid Artery) For. Rotundum (Foramen Rotundum); LOCR (lateral opticocarotid recess); LP (lamina papyracea; Maxilloeth. Sut (maxillo-ethmoidal suture); MOCR (medial opticocarotid recess); MRM (medial rectus muscle); Max. Sin. (maxillary sinus); OSL (orbitosellar line); PAL (paramedian anterior line); Post. Eth. A. (posterior ethmoidal artery); POP (posterior orbital point)

377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399

FIGURE 2. Endoscopic endonasal dissections of the ventral anteromedial and anterolateral skull base. A. Nasal stage under 0º endoscope, through the right nostril. AOP is represented at the anterior buttress of the Midd.Turb where it attaches to the Agger nasi region. B. Sup. Turb. as well as anterior and posterior ethmoidectomies have been performed, along with a wide antrostomy into the Max. Sin. NSF and both Sph. Ost. are shown. AOP is represented 3.43 +/- 0.91 cm above the intersection of the vertical plane of the lacrimal crest (black vertical dashed line) with the orthogonal plane of the maxilloethmoidal suture (black horizontal dashed line), C. Further exposure, after complete resection of the anterior wall of Sph. Sinus. Posterior Orbital Point is found to be located at the intersection between a vertical line (black dotted line) joining the Vidian Canal and the point of entrance of the Post Eth. A. into the orbit. The COFL (solid blue line) is represented by the junction of the Palatovaginal Canal, Vidian Canal and For. Rotundum from medial to lateral perspective. D. LP and intraorbital fat have been resected allowing for the exposure of the SOM, MRM, IRM. The relationship between the OSL (black solid line) and the MRM is shown. Ant. Eth. A. (anterior ethmoidal artery); Crib. Plated (cribriform plate); COLF (critical oblique foramina line); Fovea Eth. (fovea ethmoidalis); ICA (internal carotid artery); IRM( inferior rectus muscle); For. Rotundum (foramen rotundum); Lac. Crest (lacrimal crest); LOCR (lateral opticocarotid recess); LP (lamina papyracea); LS (limbus sphenoidale); Maxilloeth. Sut (maxillo-ethmoidal suture); Mid. Turb (middle turbinate) MOCR (medial opticocarotid recess); MRM (medial rectus muscle); Max. Sin. (maxillary sinus); NSF (nasoseptal flap); OC (optic canal); OSL (orbitosellar line); SOM (superior oblique muscle); Sph. Ost. (sphenoid ostium); Post. Eth. A. (posterior ethmoidal artery). Sph. Sinus (sphenoid sinus); Sup. Turb. (superior turbinate) and Unc. Proc (uncinate process).

400 401 402 403 404 405 406 407 408 409 410 411

FIGURE 3. OSL anatomical relationships from a sagittal perspective. A. The AOP is represented in relationship with the Midd. Turb. B. Sup. Turb, Midd. Turb. and Inf. Turb. have been removed, revealing Ant. and Post. Eth. Cells and the mucosa of the Max. Sinus. C. Full ethmoidectomy has been performed exposing form anterior to posterior: lacrimal duct, AOP, LP, POP and LOCR. The OSL trajectory has been represented by a solid black line. D. LP and periorbit have been resected exposing the MRM and IRM. This picture illustrates the relationship between the OSL (AOP-POP) and the MRM. The annulus of Zinn has been represented as a dashed-semicircle line. Ant. Eth. Cells (anterior ethmoidal cells); AOP (anterior orbital point); Ant. SB (anterior skull base); C (Clivus; Inf. Turb. (inferior turbinate); Infraorb. N. (infraorbital nerve); IRM (inferior rectus muscle); LOCR (lateral opticocarotid recess); LP (lamina papyracea); Maxilloeth. Sut (maxilloethmoidal suture); Midd. Turb. (middle turbinate); MOCR (medial opticocarotid recess); MRM (middle rectus muscle); Max. Sinus (maxillary sinus); POP (posterior orbital point); ON (optic

13 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445

nerve); OSL (orbitosellar line); Post. Eth. Cells (posterior ethmoidal cells); Sph. Sinus (sphenoid sinus); Sup. Turb. (superior turbinate).

FIGURE 4. Endoscopic endonasal view showing bilaterally the OSL triangulating upon the sella. LP segment an OC segment are shown. Ant. Eth. A (anterior ethmoidal artery); AOP (anterior orbital point); ICA (internal carotid artery); LOCR (lateral opticocarotid recess); LP (Lamina Papyracea); MOCR (medial opticocarotid recess); MS (maxillary sinus) ON (optic nerve); OSL (orbitosellar line); Post. Eth. A. (posterior ethmoidal artery); POP (posterior orbital point). FIGURE 5. Neuronavigation confirmation of the OSL points. A. Anterior Orbital Point (red point) reflected laterally over the lamina papyracea. B. Posterior Orbital Point (blue point). C. MOCR (green point). LOCR (lateral opticocarotid recess); LP (lamina papyracea); OC (optic canal); Post. Eth. A (posterior ethmoidal artery). FIGURE 6. Clinical case example A. T1 weighted coronal MRI showing a large frontotemporal tumor with extension along the greater sphenoid wing and into the right orbit, sphenoid sinus, petrous bone and left orbital apex. B. Axial MRI showing bilateral ON compression. C. Intraoperative EEA view showing tumor obscuring our view of the expected anatomy of the sellar and parasellar region. D. Identification of AOP (red circle), the projection of the LOCR along the Maxilloeth. Sut. (black dashed line) and POP (blue circle) along the PAL (blue dashed line). E. Intraoperative image showing POP and left OC. F-G. ON decompression following the identification of the MOCR. Neuronavigation was used during the procedure. H. Postoperative axial MRI showing bilateral ON decompression. AOP (anterior orbital point); LOCR (lateral opticocarotid recess) LP (lamina papyracea); Maxilloeth. Sut (maxilloethmoidal suture); MOCR (medial opticocarotid recess); OC (optic canal); ON (optic nerve); OSL (orbitosellar line); PAL (paramedian anterior line) Post. Eth. A (posterior ethmoidal artery): POP (posterior orbital point) FIGURE 7. Sagittal CT scan showing two different situations that might be encountered when approaching the parasellar region. A) Flat anterior skull base vs. B) steeper skull base. Red solid line represents the anterior skull base. Dashed red line represents the OSL trajectory. These different angles will be of importance when planning to access the supraoptic recess.

446 447

References:

448 449

1. Kassam A, Snyderman CH, Mintz A, Gardner P, Carrau RL. Expanded endonasal approach: the rostrocaudal axis. Part I. Crista galli to the sella turcica. Neurosurg Focus. 2005;19(1):E3.

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2. Cappabianca P, Cavallo LM, Esposito F, De Divitiis O, Messina A, De Divitiis E. Extended endoscopic endonasal approach to the midline skull base: the evolving role of transsphenoidal surgery. Adv Tech Stand Neurosurg. 2008;33:151-199.

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3. Kassam AB, Prevedello DM, Carrau RL, Synderman CH, Thomas A, Gardner P, et al. Endoscopic endonasal skull base surgery: analysis of complications in the authors initial 800 patients. J Neurosurg. 2011;114:1544-1568.

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4. Cappabianca P, Cavallo LM, de Divitiis E. Endoscopic endonasal transsphenoidal surgery. Neurosurgery 2004;55:933–940

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5.Wilson CB, Dempsey LC. Transsphenoidal microsurgical removal of 250 pituitary adenomas. J Neurosurg. 1978 Jan;48(1):13-22. 6. Elias WJ, Laws ER Jr (2000) Transsphenoidal approaches to lesions of the sella. In: Schmidek HH (ed) Operative Neurosurgical Techniques: Indications, Methods and Results. WB Saunders, Philadelphia, pp 373–384.

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7. Liu JK, Das K, Weiss MH, Laws ER Jr, Couldwell WT (2001) The history and evolution of transsphenoidal surgery. J Neurosurg 95(6):1083–1096.

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9. Rhoton AL Jr, Hardy DG, Chambers SM. Microsurgical anatomy and dissection of the sphenoid bone, cavernous sinus and sellar region. Surg Neurol. 1979;12(1):63-104.

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10. Fujii K, Chambers SM, Rhoton AL Jr. Neurovascular relationships of the sphenoid sinus. A microsurgical study. J Neurosurg. 1979;50(1):31-39.

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11. Yilmazlar S, Saraydaroglu O, Korfali E. Anatomical aspects in the transsphenoidaltransethmoidal approach to the optic canal: an anatomic-cadaveric study. J Craniomaxillofac Surg. 2012;40(7):e198-e205.

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12. Amin SM, Nasr AY, Saleh HA, Foad MM, Herzallah IR. Endoscopic orientation of the parasellar region in sphenoid sinus with ill-defined bony landmarks: an anatomic study. Skull Base. 2010;20(6):421-428.

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13. Ozcan T, Yilmazlar S, Aker S, Korfali E. Surgical limits in transnasal approach to opticocarotid region and planum sphenoidale: an anatomic cadaveric study. World Neurosurg. 2010;73(4):326-333.

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14. Peris-Celda M, Kucukyuruk B, Monroy-Sosa A, Funaki T, Valentine R, Rhoton AL Jr. The recesses of the sellar wall of the sphenoid sinus and their intracranial relationships. Neurosurgery. 2013 Dec;73(2): 117-31.

8. Wang J, Bidari S, Inoue K, Yang H, Rhoton A Jr. Extensions of the sphenoid sinus: a new classification. Neurosurgery. 2010;66(4):797-816.

15. Galletti B, Gazia F, Freni F, Sireci F, Galletti F. Endoscopic sinus surgery with and without computer assisted navigation: A retrospective study. Auris Nasus Larynx. 2018 Dec 6. 16. Wang X, Li L, Wang Y, Hu J, Zhou J, Jing Z, Wu A. Clinical Application of Multimodal Neuronavigation System in Neuroendoscope-Assisted Skull Base Chordoma Resection. Journal of Craniofacial Surgery. 2017 Sep 1;28(6):e554-7.

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17. Labib MA, Prevedello DM, Fernandez-Miranda JC, Sivakanthan S, Benet A, Morera V, Carrau R, Kassam A. The medial opticocarotid recess: an anatomic study of an endoscopic "key landmark" for the ventral cranial base. Neurosurgery. 2013 Mar;72(1): 66-76. 18. Labib MA, Prevedello DM, Carrau R, Kerr EE, Naudy C, Abou Al-Shaar H, Corsten M, Kassam A. A road map to the internal carotid artery in expanded endoscopic endonasal approaches to the ventral cranial base. Neurosurgery. 2014 Sep; 10 Suppl 3:448-71. 19. Osawa S, Rhoton AL Jr, Seker A, Shimizu S, Fujii K, Kassam AB. Microsurgical and endoscopic anatomy of the vidian canal. Neurosurgery. 2009 May;64(5 Suppl 2):385-411 20. Mahmoud M, Nader R, Al-Mefty O. Optic canal involvement in tuberculum sellae

meningiomas: influence on approach, recurrence, and visual recovery. Neurosurgery. 2010;67(3 suppl operative):ons108-ons118; discussion ons118-ons119. 21. Attia M, Kandasamy J, Jakimovski D, et al. The importance and timing of optic canal exploration and decompression during endoscopic endonasal resection of tuberculum sella and planum sphenoidale meningiomas. Neurosurgery. 2012;71 (1 suppl operative):58-67. 22. Toh ST, Lee JC. Onodi cell mucocele: rare cause of optic compressive neuropathy. Arch Otolaryngol Head Neck Surg. 2007 Nov;133(11):1153-6 23. Kassam A, Snyderman CH, Mintz A, Gardner P, Carrau RL. Expanded endonasal approach: the rostrocaudal axis. Part I. Crista galli to the sella turcica. Neurosurg Focus. 2005;19(1):E3. 24. Kassam A, Snyderman CH, Mintz A, Gardner P, Carrau RL. Expanded endonasal approach: the rostrocaudal axis. Part II. Posterior clinoids to the foramen magnum. Neurosurg Focus. 2005;19(1):E4.

OSL (total length)

Mean (mm) +/- SD Left side (n=5) 36.5 +/- 0.0

Mean (mm) +/- SD Right side (n=5) 3.8 +/- 0.0

Mean (mm) +/- SD Overall (n=10) 37.7 +/- 0.1

•

LP SEGMENT

27.09 +/- 0.0

29.9 +/- 0.1

28.2 +/- 0.05

•

OC SEGMENT

10.1 +/- 0.0

10.6 +/- 0.0

10.3 +/- 0.0

15.2 +/- 2.5

16.4 +/- 3.2

15 +/- 2.8

COFL (total length) •

PVC-VC

4.1 +/- 1.6

4.2 +/- 0.8

4.1 +/- 1.1

•

VC-FR

5.5+/- 1.5

5.1 +/- 1.1

5.3 +/- 1.2

40.9 +/- 0.6

38 +/- 0.4

39 +/- 0.1

PAL

TABLE 1. Measurements of the OSL and its segments, COFL and PAL. COFL (critic oblique foramina line), FR (foramen rotundum), OC (optic canal), LP (lamina papyracea), OSL (orbitosellar line), PAL (paramedian anterior line), PVC (palatovaginal canal), SD (standard deviation), VC (vidian canal).