Refining the anatomic boundaries of the endoscopic endonasal transpterygoid approach: the “VELPPHA area” concept

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OBJECTIVE

The endoscopic endonasal transpterygoid route has been widely evaluated in cadavers, and it is currently used during surgery for specific diseases involving the lateral skull base. Identification of the petrous segment of the internal carotid artery (ICA) is a key step during this approach, and the vidian nerve (VN) has been described as a principal landmark for safe endonasal localization of the petrous ICA at the level of the foramen lacerum. However, the relationship of the VN to the ICA at this level is complex as well as variable and has not been described in the pertinent literature. Accordingly, the authors undertook this purely anatomical study to detail and quantify the peri-lacerum anatomy as seen via an endoscopic endonasal transpterygoid pathway.

METHODS

Eight human anatomical specimens (16 sides) were dissected endonasally under direct endoscopic visualization. Anatomical landmarks of the VN and the posterior end of the vidian canal (VC) during the endoscopic endonasal transpterygoid approach were described, quantitative anatomical data were compiled, and a schematic classification of the most relevant structures encountered was proposed.

RESULTS

The endoscopic endonasal transpterygoid approach was used to describe the different anatomical structures surrounding the anterior genu of the petrous ICA. Five key anatomical structures were identified and described: the VN, the eustachian tube, the foramen lacerum, the petroclival fissure, and the pharyngobasilar fascia. These structures were specifically quantified and summarized in a schematic acronym—VELPPHA—to describe the area. The VELPPHA area is a dense fibrocartilaginous space around the inferior compartment of the foramen lacerum that can be reached by following the VC posteriorly; this area represents the posterior limits of the transpterygoid approach and, of utmost importance, no neurovascular structures were observed through the VELPPHA area in this study, indicating that it should be a safe zone for surgery in the posterior end of the endoscopic endonasal transpterygoid approach.

CONCLUSIONS

The VELPPHA area represents the posterior limits of the endoscopic endonasal transpterygoid approach. Early identification of this area can enhance the safety of the endoscopic endonasal transpterygoid approach expanded to the lateral aspect of the skull base, especially when treating patients with poorly pneumatized sphenoid sinuses.

ABBREVIATIONS ET = eustachian tube; FL = foramen lacerum; ICA = internal carotid artery; VC = vidian canal; VELPPHA = vidian nerve, eustachian tube, foramen lacerum, petroclival fissure, and pharyngobasilar fascia; VN = vidian nerve.

Article Information

Correspondence Ariel Kaen: Hospital Universitario Virgen del Rocío, Sevilla, Spain. kaenariel@hotmail.com.

INCLUDE WHEN CITING Published online September 21, 2018; DOI: 10.3171/2018.4.JNS173070.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Endonasal endoscopic view of the VN and VC during the initial steps of the approach (A) and at a later phase (B). ET = eustachian tube; For. = foramen; N. = nerve; paICA = parasellar ICA; pICA = paraclival ICA; Pw = pterygoid wedge. Copyright Ariel Kaen. Published with permission. Figure is available in color online only.

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    Endoscopic endonasal transpterygoid approach. Stepwise dissection to the VELPPHA area. The main anatomical landmarks in the right nasal cavity are shown (A). In step 1, the anterior end of the VC is exposed after moving the pterygopalatine fossa content laterally (B). In step 2, the VC is followed in an anterior to posterior direction in order to reach the FL (C). In step 3, the VELPPHA area is exposed and the surrounding neurovascular and ligamentous structures are visible (D). Copyright Ariel Kaen. Published with permission. Figure is available in color online only.

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    A: Image-guidance screenshots depicting the main quantitative measurement obtained. B: Axial CT images were used to calculate VC length (red arrows) at the level of the petrous ICA (yellow asterisk). Figure is available in color online only.

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    A: A 45° endoscopic view of the endonasal transpterygoid cadaveric dissection showing the VN going from the pterygopalatine fossa to the FL. Due to the trajectory from medial to lateral and from inferior to superior, in the posterior limits of the transpterygoid approach, the nerve crosses in front of the horizontal portion of the carotid and is then placed on top. B: Lateral schematic illustration facilitating understanding of the posterior limit of the VC along the pterygoid wedge. The VN passes along the anterior half of the upper surface of the horizontal segment of the ICA before turning downward along the anterior surface of the artery to reach the FL. paICA = parasellar ICA; pICA = paraclival ICA; Pw = pterygoid wedge. Copyright Ariel Kaen. Published with permission. Figure is available in color online only.

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    A: Coronal illustration view showing how the vertical fibers of the VELPPHA area attach to the ET, especially the medial ones (yellow). B: A 45° endoscopic view showing the course of the VN and the close relationship with the horizontal petrous ICA. The anterior and medial fibers of the VELPPHA area come from the fibrocartilaginous part of the ET. For definitions of FL2 and FL3, refer to the Quantitative Assessment and Statistical Analysis subsection of Methods. hICA = horizontal petrous ICA; pICA = paraclival ICA. Copyright Ariel Kaen. Published with permission. Figure is available in color online only.

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    A: The lacerum anatomy shown in a formalin-fixed cadaveric head. The VELPPHA area (green zone) presents a group of fibers that are distributed horizontally to the FL. The most superficial fibers come from the pharyngobasilar fascia (black arrows), while the deeper fibers originate in the petroclival fissure. B: An endoscopic view of the completely dissected petroclival fissure showing the posterior horizontal fibers of the VELPPHA area attached to the FL in a deeper plane (yellow arrows). pICA = paraclival ICA. Copyright Ariel Kaen. Published with permission. Figure is available in color online only.

  • View in gallery

    A: A 45° endoscopic view of the pICA. It can be observed how the VN is surrounded by the anterior fibers (blue) that extend from the FL toward the pterygoid wedge. The medial fibers (yellow) extend toward the ET, and finally, the posterior fibers adhere to the posterior border of the FL with the union of the petrous apex. B: An axial illustration view of the vertical fibers showing the 3 different attachments: the pterygoid wedge, the eustachian tube, and the petrous apex. PA = petrous apex; Pw = pterygoid wedge. Copyright Ariel Kaen. Published with permission. Figure is available in color online only.

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