Endoscopic endonasal approach (EEA) in the sagittal plane: from the frontal sinus to the odontoid process. The sphenoid sinus is the starting point for most endonasal approaches. The pituitary gland lies within the sphenoid sinus. From here we can extend the approaches towards the suprasellar region, retroinfundibular space, and anterior skull base. The outer table of the frontal sinus is the anterior limit to the anterior skull base approach. The endonasal approach can extend inferiorly to the clival region, ventral aspect of the posterior fossa, and craniocervical junction. (Image courtesy of JC Fernandez-Miranda)