ons42 | VOLUME 65 | OPERATIVE NEUROSURGERY 1 | DECEMBER 2009 www.neurosurgery-online.com ANATOMY Anatomic Report Matteo de Notaris, M.D. Division of Neurosurgery, Department of Neurological Sciences, Università degli Studi di Napoli Federico II, Naples, Italy Luigi Maria Cavallo, M.D., Ph.D. Division of Neurosurgery, Department of Neurological Sciences, Università degli Studi di Napoli Federico II, Naples, Italy Alberto Prats-Galino, M.D. Department of Human Anatomy and Embryology, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain Isabella Esposito, M.D. Division of Neurosurgery, Department of Neurological Sciences, Università degli Studi di Napoli Federico II, Naples, Italy Arnau Benet, M.D. Department of Human Anatomy and Embryology, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain José Poblete, M.D. Department of Neurosurgery, Hospital Clinic, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain Vinicio Valente, M.D. Division of Neurosurgery, Ospedale Civile dell’Annunziata, Cosenza, Italy Joan Berenguer Gonzalez, M.D. Department of Neuroradiology, Hospital Clinic, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain Enrique Ferrer, M.D. Department of Neurosurgery, Hospital Clinic, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain Paolo Cappabianca, M.D. Division of Neurosurgery, Department of Neurological Sciences, Università degli Studi di Napoli Federico II, Naples, Italy Reprint requests: Luigi Maria Cavallo, M.D., Ph.D., Division of Neurosurgery, Department of Neurological Sciences, Università degli Studi di Napoli Federico II, Via Pansini 5, 80131 Naples, Italy. Email: lcavallo@unina.it Received, July 24, 2008. Accepted, December 23, 2008. Copyright © 2009 by the Congress of Neurological Surgeons S urgical treatment of lesions involving the clivus and compressing the anterior and/ or lateral brainstem surface is still consid- ered a challenge for the neurosurgeon, who must navigate between critical neurovascular structures. Chordomas, chondrosarcomas, and meningiomas are some of the lesions that can arise from the clival region and extend toward the anterolateral surface of the brainstem (59). Such tumors may expand superiorly to reach the sellar and suprasellar areas, inferiorly to the foramen magnum and craniovertebral junction, and laterally to the middle cranial fossa, tento- rium, and cerebellopontine angle. In these cases, use of a single surgical corridor may not allow exposure of the entire lesion. Advances in neuroimaging and neuronaviga- tion tools (43) and intraoperative cranial nerve monitoring (56, 58) have allowed safer surgical approaches and improved the outcome of lesions that, a few decades ago, were considered to be almost inaccessible. At the same time, progress in cranial base surgery has resulted in improvement and remodeling of the approaches to the cranial base (19, 54). Traditional microsur- gical routes that are used to remove lesions in this area can be divided into 3 main groups: anterior, anterolateral, and posterolateral; the choice of the approach depends on the location and extension of the tumor (2, 3, 13, 22, 24, 45, 60). These approaches can require extensive soft tissue osseous disruption and brain mobiliza- ENDOSCOPIC ENDONASAL TRANSCLIVAL APPROACH AND RETROSIGMOID APPROACH TO THE CLIVAL AND PETROCLIVAL REGIONS OBJECTIVE: The removal of clival lesions, mainly those located intradurally and with a limited lateral extension, may be challenging because of the lack of a surgical corri- dor that would allow exposure of the entire lesion surface. In this anatomic study, we explored the clival/petroclival area and the cerebellopontine angle via both the endonasal and retrosigmoid endoscopic routes, aiming to describe the respective degree of expo- sure and visual limitations. METHODS: Twelve fresh cadaver heads were positioned to simulate a semisitting posi- tion, thus enabling the use of both endonasal and retrosigmoid routes, which were explored using a 4-mm rigid endoscope as the sole visualizing tool. RESULTS: The comparison of the 2 endoscopic surgical views (endonasal and retrosig- moid) allowed us to define 3 subregions over the clival area (cranial, middle, and cau- dal levels) when explored via the endonasal route. The definition of these subregions was based on the identification of some anatomic landmarks (the internal carotid artery from the lacerum to the intradural segment, the abducens nerve, and the hypoglossal canal) that limit the bone opening via the endonasal route and the natural well-estab- lished corridors via the retrosigmoid route. CONCLUSION: Different endoscopic surgical corridors can be delineated with the endonasal transclival and retrosigmoid approaches to the clival/petroclival area. Some relevant neurovascular structures may limit the extension of the approach and the view via both routes. The combination of the 2 approaches may improve the visualization in this challenging area. KEY WORDS: Endoscopic cranial base surgery, Endoscopic endonasal surgery, Endoscopic retrosigmoid approach, Endoscopic skull base surgery, Endoscopic transsphenoidal surgery, Petroclival region Neurosurgery 65[ONS Suppl 1]:ons42–ons52, 2009 DOI: 10.1227/01.NEU.0000347001.62158.57