Endoscopic Endonasal Approach to Foramen Lacerum: Anatomical and Technical Note

Introduction: Foramen lacerum is the space surrounded by the pterygoid process of the sphenoid bone anteriorly, petrous apex of the temporal bone posterolaterally and clival part of the occipital bone inferomedially. The lower part of this foramen is filled with fibrocartilaginous tissues and the upper part has the internal carotid artery (ICA) passing through. From the endoscopic endonasal perspective, the foramen lacerum is a key structure in the coronal plane approach. In this report, we describe the anatomic and technical nuances to safely and effectively expose the foramen lacerum to gain better access to medial, supra- and infrapetrous apex regions.

Methods: Five colored silicone-injected anatomical specimens were dissected using a transpterygoid approach to the foramen lacerum region in a stepwise manner. 3D-CT reconstruction technique was used to demonstrate the bony landmarks from different perspectives. Representative cases were selected from our clinical database to illustrate the application of our findings.

Results: The junction of the fibrotic tissues of the petroclival fissure and the pterygosphenoidal fissure lead to the inferomedial margin of the foramen lacerum, just below the lacerum ICA. The posterior end of the vidian canal and nerve are reliable landmarks leading to the anterolateral margin of the foramen lacerum. The bone that remains between the vidian nerve and pterygosphenoidal/petroclival fissure junction forms the anterior wall of the foramen lacerum, and has to be removed to uncover the inferior aspect of the lacerum ICA. Superior and lateral to the vidian nerve, the lingual process and petrolingual ligament form the lateral wall of the foramen lacerum. V2 runs just lateral to the lingual process in the interdural space of the middle fossa floor. Removal of the lingual process is crucial to maximize the lateral mobilization of the paraclival and lacerum ICA to obtain better access to the medial petrous apex behind the ICA. For full mobilization of the lacerum ICA, as required to access the inferior petroclival region, inferior petrous bone, and jugular foramen, it is necessary to transect the fibrotic tissue (pterygosphenoidal/petroclival fissure junction) that connects with the Eustachian tube and forms the inferior aspect of the foramen lacerum. Lateral to the lingual process, we find from medial to lateral: the petrosphenoidal fissure, V3 strut, and foramen ovale. V3 strut is the piece of bone that separates foramen ovale from the petrosphenoidal fissure and foramen lacerum. The foramen and vein of Vesalius (or sphenoidal emissary foramen and vein), when present, are located in the anterior aspect of V3 strut. The vein of Vesalius, which connects the cavernous sinus with the pterygoid plexus, has to be coagulated when extending the approach along the floor of the middle fossa from foramen lacerum to ovale. Based on these landmarks, several illustrative cases are presented to show the various approaches to and around foramen lacerum.

Conclusion: The proposed anatomic landmarks may help to widely expose the foramen lacerum while avoiding injury to the ICA, to effectively remove lesions involving the medial, supra-, and infrapetrous regions.