Objective: The objective of this study was to recognize the endoscopic anatomy of the clival region of the skull base and its neurovascular relations, which will make us able to perform safer and minimal invasive endoscopic approaches to this region with lower rate of complications.

Materials and methods: Six fresh cadavers were studied (n = 5). We approached the clivus by performing binostril extended endoscopic endonasal approach. After locating the sphenoid sinus as a key point, the vomer was totally removed to expose the clival region located inferiorly to the sphenoid sinus. Mucosal incision is done vertically from the sphenoidal portion the clivus caudally to the inferior portion of nasal cavity just medially to vidian nerve. The mucosal flap is then dissected and retracted. The clivus was resected until the foramen magnum inferiorly. The lateral limit of the resection is the paraclival portion of the internal carotid artery (ICA).The dura and the meningohypophyseal artery is exposed. A vertical dural incision was done and retracted laterally to expose the intradural structures. The prepontine cistern and basilar artery were visualized.

Results: The clivus was best localized by orienting the endoscope +15 degrees rostrally. After resecting the inferior wall of the sphenoid sinus and vomer and the overlying mucosa is retracted laterally until the vidian nerve, we obtained sufficient exposure of the clivus. The safe lateral limit of the surgical corridor was the vidian nerve. The clivus is resected until the foramen magnum inferiorly. The safe lateral limit of the resection in this step was the proximal cavernous and the distal petrosal portions of the ICA. This resection provided us with a wide exposure of the clival dura. The basilar plexus, the abducens nerve (sixth cranial nerve) passing through the basilar plexus, and the paraclival portion of the ICA can be injured when careful dissection is not performed. After dural incision, the prepontine cistern and the basilar artery were able to be exposed widely.

Conclusion: Binostril extended endoscopic endonasal approach is an appropriate approach to the clival region of the skull base. With good knowledge of the endoscopic anatomic features of this region and its neurovascular relations, surgical procedures can be performed safely with more minimal invasiveness.