Surgical Anatomy of the Paralacerum Region and its Relevance for Endoscopic Endonasal Skull Base Surgery

Objective: The anatomy of the foramen lacerum (FL) has been recently investigated, providing surgical landmarks for its safe exposure in endoscopic endonasal skull base surgery. While the anterior and medial aspect of the FL have been well described, a thorough investigation of its lateral aspect, namely the paralacerum region, is lacking. The purpose of this study was therefore to provide a detailed investigation of the surgical anatomy of the paralacerum region, and to propose key landmarks helping the surgeon navigate this critical region. Methods: This anatomical study comprised a morphometric investigation of dry skulls (80 sides), anatomical dissections (20 sides), and radiological analysis using high-resolution computed tomography scans (40 sides). The relevant surgical anatomy was studied endo- and exocranially to investigate the osseous, fibrocartilaginous, and neurovascular relationships of the paralacerum region. In addition, two illustrative clinical cases are presented. Results: The paralacerum region contains the lingual process (LP), vidian nerve (VN), petrosphenoidal fissure, mandibular strut (MS), foramen ovale (FO), V3, and the petrous carotid. The LP was present in 69%, absent in 9%, and present as an ossified ring in 20% of cases. The petrosphenoidal triangle, delineated by the petrosphenoidal fissure inferiorly, and the VN superiorly, points toward the lateral aspect of the lacerum ICA, and serves as a reliable landmark to approach the paralacerum region safely. In fact, it is used to sequentially expose from medial to lateral: the MS, V3 and the middle cranial fossa floor. The mean angle of the petrosphenoidal triangle apex is 88 ± 2°. The mean drilling distance of the MS[JCFM1] [RA2] from medial to lateral is 6 ± 1mm. The FO is found lateral to the MS and just anterior to the FL in 76%, and at the same level in 24% of cases. In the depth of the paralacerum region, care is taken not to injure the petrous ICA, which runs posterolaterally (mean angle between VN and petrous ICA in the axial plane: 131 ± 6°), and slightly caudally (mean angle between paraclival ICA and petrous ICA in the coronal plane: 120 ± 8°). Conclusion: This study provides important anatomical descriptions, measurements, and key landmarks to safely access the paralacerum region from an endoscopic endonasal perspective. By utilizing the petrosphenoidal triangle, the paralacerum region can be sequentially exposed from medial to lateral. Publication History Article published online: 27 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany