Skull base as seen from the transcranial or dorsal view. The anatomical limits of the endonasal approach are the optic nerves in the anterior skull base; the lateral wall of the cavernous sinus in the parasellar region; the free edge of the tentorium (anterior petroclinoidal ligament) in the interpeduncular region; the trigeminal ganglion and branches in the middle fossa. Understanding the anatomical limitations of the endonasal route is the basis for appropriate selection and combination of approaches. (Image courtesy of JC Fernandez-Miranda)