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Objective: The anatomic features of transsphenoidal approach are reviewed, focusing on the microsurgical anatomy of suprasellar and parasellar structures. Pertinent microsurgical anatomy is described for neurosurgeons to successfully extend a standard transsphenoidal approach for treatment of lesions including the region of the tuberculum sellae, planum sphenoidale, supradiaphragmatic intradural space, and medial cavernous sinus., Methods: 15 specimens (30 sides) from formalin fixed cadaveric heads and 20 adult dry skulls (40 sides) were observed. According to the need for the extend transsphenoidal approach, the sellar and parasellar region: the planum sphenoidale and the supradiaphragmatic area, medial part of cavernous sinus were studied. Special emphases were put on the relation of the cranial nerve and blood vessel structures surrounding the sellar. Meanwhile, we made the cast specimen of the blood vessel and studied the structure character of the internal carotid artery in the cavernous sinus., Results: Posterior ethmoidal could be exit as para or suprasphenoidal ethmoidal air cell. It will be important for extending the transsphenoidal approach. The mean distance between two optic canal is 15.7 +/- 3.2 mm (11.0 - 18.0 mm), the distance of internal carotid artery at tuberculum cellae level is 13.9 +/- 3.8 mm (10.0 - 17.0 mm), the mean distance between tuberculum cellae and the posterior rim of cribriform plate is 23.3 +/- 3.2 mm, the included angle between sagittal plane and optic canal is 36.3 degrees +/- 1.6 degrees , with the anatomy research data give the clue that the bone window should be made as the shape of "[see text]"., Conclusions: Expending transsphenoidal approach is suitable for medium and small lesions growing along the centre line which expand to para sellar, anterior sellar and sphenoid platform. That hypophysis has close relation with internal carotid artery during expending transsphenoidal approach to cavernous sinus increase the risk of operation. The carotid artery and abducent nerve are the easiest structures to be damaged during the operation.