The sphenoid bony landmarks are important for endoscopic orientation in skull 
base surgery but show a wide range of variations. We aimed to describe an 
instructional model for the endoscopic parasellar anatomy in sphenoid sinuses 
with ill-defined bony landmarks. Five preserved injected cadaveric heads and 
four sides of dry skulls were studied endoscopically via transethmoid, 
transsphenoidal approach. The parasellar region was exposed by drilling along 
the maxillary nerve (V2) canal [the length of the foramen rotundum (FR) between 
the middle cranial fossa and the pterygopalatine fossa]. This was achieved by 
drilling in the inferior part of the lateral wall of posterior ethmoids 
immediately above the sphenopalatine foramen. Cavernous V2 was traced to the 
paraclival internal carotid artery (ICA). Cavernous sinus (CS) apex was exposed 
by drilling a triangle bounded by V2 and its canal inferiorly, bone between FR 
and superior orbital fissure (SOF) anteriorly, and ophthalmic nerve (V1) 
superiorly. Drilling was continued toward the annulus of Zinn (AZ) and optic 
nerve superiorly and over the intracavernous ICA posteriorly. Endoscopic 
measurements between V2, SOF, AZ, and opticocarotid recess were obtained. 
Endoscopic systematic orientation of parasellar anatomy is presented that can be 
helpful for approaching sphenoid sinus with ill-defined bony landmarks.