LABORATORY INVESTIGATION J Neurosurg 130:1699–1709, 2019 T he endoscopic endonasal approach (EEA) and its transpterygoid and transclival extensions have revolutionized the surgical treatment of skull base lesions. 1,4, 26–28,38,46 Through providing a wide panoramic view, avoidance of skin incisions, minimal bone resection, and less manipulation and retraction of neurovascular structures, the EEA has reduced complications and im- proved patient outcome. 3,6,14,43,49 Despite these benefts, the shift from the classic 3D transcranial microsurgical perspective to the 2D panoram- ic endonasal view may lead to disorientation and confu- sion during EEA. 9,11,16 This becomes evident when large le- sions with lateral extension obscure the natural anatomical landmarks or distort the natural course of critical struc- tures, such as the internal carotid artery (ICA). This can result in an increased risk of ICA injury, which is the most dreaded complication of EEA. 12 On the other hand, eff- cient localization of the ICA is a crucial step during the ex- panded endonasal approaches to the clivus, petrous apex, and Meckel’s cave. 24,27–29,39 The incorporation of surgical ABBREVIATIONS EEA = endoscopic endonasal approach; ICA = internal carotid artery. SUBMITTED September 28, 2017. ACCEPTED December 5, 2017. INCLUDE WHEN CITING Published online May 18, 2018; DOI: 10.3171/2017.12.JNS172435. The pterygoclival ligament: a novel landmark for localization of the internal carotid artery during the endoscopic endonasal approach Ali Tayebi Meybodi, MD, 1 Andrew S. Little, MD, 1 Vera Vigo, MD, 2 Arnau Benet, MD, 1 Sofa Kakaizada, 2 and Michael T. Lawton, MD 1 1 Department of Neurological Surgery, Barrow Neurological Institute, Phoenix, Arizona; and 2 Skull Base and Cerebrovascular Laboratory, University of California, San Francisco, California OBJECTIVE The transpterygoid extension of the endoscopic endonasal approach provides exposure of the petrous apex, Meckel’s cave, paraclival area, and the infratemporal fossa. Safe and ef fcient localization of the lacerum segment of the internal carotid artery (ICA) is a crucial part of such exposure. The aim of this study is to introduce a novel land- mark for localization of the lacerum ICA. METHODS Ten cadaveric heads were prepared for transnasal endoscopic dissection. The foor of the sphenoid sinus was drilled to expose an extension of the pharyngobasilar fascia between the sphenoid foor and the pterygoid process (the pterygoclival ligament). Several features of the pterygoclival ligament were assessed. In addition, 31 dry skulls were studied to assess features of the bony groove harboring the pterygoclival ligament. RESULTS The pterygoclival ligament was identifed bilaterally during drilling of the sphenoid foor in all specimens. The ligament started a few millimeters posterior to the posterior end of the vomer alae and invariably extended posterolater- ally and superiorly to blend into the fbrous tissue around the lacerum ICA. The mean length of the ligament was 10.5 ± 1.7 mm. The mean distance between the anterior end of the ligament and midline was 5.2 ± 1.2 mm. The mean distance between the posterior end of the ligament and midline was 12.3 ± 1.4 mm. The bony pterygoclival groove was identifed at the confuence of the vomer, pterygoid process of the sphenoid, and basilar part of the occipital bone, running from posterolateral to anteromedial. The mean length of the groove was 7.7 ± 1.8 mm. Its posterolateral end faced the antero- medial aspect of the foramen lacerum medial to the posterior end of the vidian canal. A clinical case illustration is also provided. CONCLUSIONS The pterygoclival ligament is a consistent landmark for localization of the lacerum ICA. It may be used as an adjunct or alternative to the vidian nerve to localize the ICA during endoscopic endonasal surgery. https://thejns.org/doi/abs/10.3171/2017.12.JNS172435 KEYWORDS vidian nerve; vidian artery; vidian canal; transpterygoid approach; sphenoid sinus; pharyngobasilar fascia; surgical technique J Neurosurg Volume 130 • May 2019 1699 ©AANS 2019, except where prohibited by US copyright law Unauthenticated | Downloaded 05/17/22 05:12 AM UTC