Abstract: Objective To explore the feasibility and operation methods of interforniceal diaterma keyhole approach for operative therapy of apex basilar artery aneurysm. Methods Interforniceal diaterma keyhole approach was designed to interpeduncular cistern with diaterma incision from tuber cinereum to posterior perforated substance and between bilateral mammillary bodies. The simulation operations of interforniceal diaterma keyhole approach were performed in 16 cadaveric heads by assisting with Stryker neuronavigation. Anatomic structures were observed by surgical microscope and measured by Stryker neuronavigation in the keyhole approach operations. Results The operations of interforniceal diaterma keyhole approach could be accomplished successfully in 16 cadaveric heads. The distances from bregma to superior margin of interventricular foramen, superior margin of adhaesio interthalamica, mammillary body, superior margin of aqueduct of midbrain and bifurcation of basilar artery were （68.4±4.6）mm, (66.3±6.0)mm,(86.3±5.3)mm, (82.0±7.6)mm and (91.8±5.0)mm respectively. The length of surgical window of diaterma was （9.5±2.6）mm from tuber cinereum to posterior perforated substance between bilateral mamillary bodies. The apex of basilar artery, P1 and P2 of posterior cerebral artery, superior cerebellar artery, posterior communicating artery and perforating branches from them could be exposed distinctly in interpeduncular cistern. The scope of operative exposure region was front to clivus and dorsum sellae by dissected the Liliequist panniculus, lateral to oculomotor nerve and posterior to interpeduncular fossa. The bifurcation of basilar artery apex was deviation to left in 68.8%. The bilateral posterior cerebral arteries were oblique to the anterolateral in 68.8%. There were 1-4 perforating branches from the apex of basilar artery in the included angle of bilateral posterior cerebral arteries. Conclusion Interforniceal diaterma keyho

Key words: Keyhole approach, Basilar artery, Aneurysm, Microanatomy, Human