Step-by-step approach to the anterior skull base. The nasal septum has been removed to communicate left and right nasal cavities. The left sinonasal structures, including the middle turbinate, remain intact. The sphenoid sinus has not been opened, and the right sphenoid ostium can be identified. The posterior ethmoidal cells have been removed to expose the lamina papyracea, frontal sinus recess, olfactory sulcus, lateral lamella, and anterior ethmoidal artery. (Image courtesy of JC Fernandez-Miranda)