Central skull base anatomy as seen through the endoscope M. Tschabitscher 1 , R. J. Galzio 2 1 Microsurgical & Endoscopic Anatomy, University of Vienna, Vienna, Austria 2 Department of Neurosurgery, University of LAquila, LAquila, Italy Introduction The endoscope may provide new effective thera- peutic strategies and less invasive approaches. This instrument, however, provides quite a different per- spective of the anatomical structures normally seen with the operating microscope, thus requiring dif- ferent reference points. The keyhole concept dictates that anatomical variation from patient to patient often requires different endoscopic approaches to the same target. The best approach to various lesions of the central skull base is determined only after precise analysis of a given patients anatomy and clinical circumstances. The following describes three different endoscopic approaches. Material and method The equipment used throughout the prepara- tion of the anatomical studies consisted of the HOPKINS Ò rod lens telescope, 0  , 30  and 45  view, diameter 4 mm of Karl Storz Company, Tuttlingen, Germany, Cold Light Fountains and Accessories for Video Documentation, KARL STORZ Endovision, IMAGE-1 Video Camera System and Accessories for Illumination, Documentation and Data Storage. Fresh (non-fixed) cadaver heads were employed, and only the arterial system was injected with colored rubber. Access to each region was similar to that achieved by standard neurosurgical techniques. Supraorbital–subfrontal approach Certain anatomical conditions are required for exploring central skull base structures endoscopi- cally (Fig. 1): 1. The window between the pituitary stalk, the 2nd cranial nerve and the internal carotid artery or the 3rd cranial nerve must be of sufficient size; 2. The dorsum sellae must not be too prominent. The anterior cranial fossa is bordered posteriorly by the lesser wing of the sphenoid, which also marks the junction of the frontal and temporal lobes, or direct access to the sylvian fissure. After splitting the arachnoid, the entire M1 segment may be seen endoscopically. The 3rd cranial nerve comes into view medially. It enters the roof of the cavernous sinus (through Langs trough) (Fig. 2). Between the 3rd cranial nerve and the internal carotid Liliequists membrane may be split, giving access to the posterior cranial fossa. Depending on how medially or how laterally the supraorbital craniotomy is placed, the interpe- duncular fossa is accessed along the posterior com- municating artery (Fig. 3). There, the tip of the basilar artery (and its terminal branches), the mam- millary bodies, and tuber cinereum are seen. In keeping with the keyhole concept, the midline is better visualized from a more lateral approach than medially. W Dolenc / Rogers (eds.) Cavernous Sinus