Endoscopic endonasal approach through the left nostril. The middle turbinate and the inferior half of the superior turbinate have been removed. The sphenoid ostium is now easily identified. The bulla ethmoidalis has been partially resected but the uncinate process remains intact. The choana, now, is the opening between the nasal cavity and the nasopharynx. The mucosa that covers the rostrum of the sphenoid and sphenoid crest contains the posterior nasal artery, which provides the main vascular supply to the nasal septum. Preservation of this mucosa is key when harvesting a nasoseptal flap for skull base reconstruction. (Image courtesy of JC Fernandez-Miranda)