| Objective:To get detailed anatomical date of antertaior clinoid process and its surrounding structures. To explore the methods and significance of anterior clinoidectomy, and to get data of individual anatomical relations of bones, nerves, vessels and duramater in the areas of anterior clinoid process by statistics and analysis. To provide the anatomical evidence and reference for operations in the areas of anterior clinoid process.Methods:1. The osseous structures of anterior clinoid process were observed and measured in 30 sides of dry adult cadaveric head specimens.2. Ten formalin-fixed adult cadaveric heads specimens after perfusion of the arteries and veins with colored silicone were dissected layer by layer under microscope via orbital-zygomatic approach. Measured the anatomical structures in the areas of anterior clinoid process accurately and take photos. Observe and measure the impoving exposure of the seller area and upper clivus after clinoidectomy.3. All date were statistically processed and presented in the mean (range and measured value) style.Results:1. Anterior clinoid process was a taper structure, posterior and medial continuation of the lesser wing of sphenoid bone with its length, width and thickness being 9.32±1.17 (7.12～11.30) mm,12.16±2.37 (8.54～12.92)mm,5.30±0.91 (3.22～7.64)mm respectively。Bone bridge could be found between the ACP and both middle and posterior clinoid processes. ACP pneumatization was found in 10% of all sides, and the air space might communicate with the sphenoid sinus and ethmoid sinus.2. Clinoid space was taper lacuna after anterior clinoid process was stripped,.it could provide about 0.8～1.0cm3 additional operating space. The four length of clinoid space basic margin were 8.68±1.46 (6.22～11.24)mm,5.06±1.39 (3.62～8.08) mm,6.40±1.12 (4.98～10.66)mm,9.62±1.83 (5.46～13.80)mm respectively, and its height was 8.46±1.29 (6.08～12.94)mm.3. The date of ICA-OC triangle before and after removal of the anterior clinoid process, respectively, were:optic nerve length 8.93±2.48mm and 18.88±2.46 mm, internal carotid artery length 10.24±1.79mm and 15.06±2.91mm.4. The distal dural ring was a thick membrane that fused with the adventitia of the ICA, with the thickness of 0.48±0.07mm; The proximal dural ring loosely surrounded the clinoid segment of ICA and admitted a variable number of veins from the cavernous plexus that accompanied with this segment. The thickness of the proximal dural ring was 0.26±0.05 mm.5. The clinoid segment of the ICA was between the distal dural ring and the proximal dural ring, with the length of 5.84±1.19mm.6. The ophthalmic artery originated from the supraclinoid segment of internal carotid artery,90%of them arose from the medial third of superior surface of ICA. There were 16 sides ophthalmic artery origin locating medial inferior to optic nerve, and 4 sides locating lateral inferior to optic nerve.7. There were four walls and two openings for optic canal.The length of the canal wall was11.14±1.37(8.60～14.28)mm,9.06±1.02(7.46～12.08)mm,9.74±1.16 (7.76～11.08)mm,5.12±1.94 (3.18～9.52)mm in internal, externa,superior and inferior walls respectively.Post of optic canal superior wall,dural fold formed falciform ligament, the width(anteroposterior diameter)was 2.49～0.74(1.18～3.96)mm, The optic nerve's impressions formed by falciform ligament were found(85%). The adjacent structure of internal wall was best complicated.The ophthalmicartery commonly courses beneath the optic nerve in the dura.From cranial opening to orbital opening,its caliber varies littlely.And most of it courses from inside to outside under the optic nerve.8. The superior orbital fissure(SOF) was a triangular cleft and the length of the superior side, the medial side and the lateral side of the SOF were 17.32±3.07 (12.36～26.18)mm,6.48±1.16(4.20～8.54)mm,19.90±4.78(12.96～27.14)mm respectively. The SOF was divided into three areas by the annular tendon. The lateral area was passed by the troehlear, fronial and lacrimal nerves and the superior ophthalmic vein. The entral area transmit the superior and inferior of divisions of the oculomotor nerve, the abducent and nasociliary nerves. The inferior area was passed by the inferior ophthalmic vein. The diameter of inferior branch of oculomotor nerve was the largest(1.64±0.37mm), in contrast the lacrimal nerve was the smallest(0.52±0.17mm).Conclusions:1. The ACP and its adjacent structures are very complex, and ACP of Chinese skulls are highly variable. Preoperative imaging examination is necessary to evaluate pneumatization of the ACP. Variations of the bone bridge should be kept in mind before and during the operation.2. Anterior clinoidectomy is very important for improving the exposure of seller region and upper clivus. Clinoid space is the essential pathway into cavernous sinus by superior approach, via which the paraclinoid segment of ICA and ophthalmic artery origin can be exposed thoroughly.3. The optic strut is the iconography landmark to define the distal dural ring, which is important to extinguish intra-and extradural hemorrhage.4. Surgical clipping of carotid-ophthalmic aneurysms through contralateral approach can be effected by some factors:ophthalmic artery origin, optic chiasma and prechiasmatic space. Contralateral approach can be applied to clip some small non-rupture carotid-ophthalmic aneurysms arising from the medial third of superior surface of ICA.5. The falciform ligment, sheath of optic nerve and anular tendon should be incised in optic canal decompression. The incision shuoud be located on the supralateral wall of the sheath of optic nerve to avoid destroy ophthalmic artery.6. To avoid destroying the lacrimal nerve, frontal nerve, trochlear nerve and superior ophthalmic vein, temporal tip dural fold (depth≤5 mm) should be dissected towards anterior clinoid process clinging to SOF. The central area of SOF could be exposed completely with the incision of annular tendon between the origin of the superior rectus and lateral rectus muscles.
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