| The decompression of optic canal included transcranial and externaltransethmo-sphenoid two operation approaches,we chose the two operationapproaches of transpterional-sylvian and external transethmo-sphenoiddecompression of optic canal to study. Objective: To study the microanatomicalstructures of transpterional-sylvian and external transethmo-sphenoid decompressionof optic canal,link them with clinic to compare,find their advantages anddisadvantages in order to offer laboratory data to clinic in choice of the betterapproach of optic canal decompression. Method: The fifteen adult Cadaver heads(male 10, female 5) were dissected with the aid of an operating microscope accordingto the operation approach. All specimens previously had been embalmed in a formalinsolution. Result:①sylvian fissure The distance between the middle piece of M1and sphenoidal crest: 10.35±2.28mm.The diameter of M1:3.28±0.64mm.The lengthof M1: 21.26±4.62mm.The branches of the M1 segment were classified into twotypes: Lateral Leuticulostriate Arteries(LLAs) and Cortical Arteries. The directbranch of LLAs: 7.90±2.25.The average angle of the genu measured: 109.8°±13.6°.The angle between the superior and inferior trunks of M2 segment was found:left97.1°4±22.7°.The superior trunk's diameter: 2.09±0.35mm.The inferior trunk'sdiameter: 2.11±0.36mm.②anterior clinoid process The length, width andthickness were9.62±1.16mm, 12.23±1.96mm, 5.34±1.08mm,respectively.Oculomotor nerve was the nearest cranial nerve to anterior clinoid process incavernous sinus,and the distance was 1.87±0.73mm. The right and left combinedmean values±standard error of the mean before and after removal of the anteriorclinoid process, respectively, were: optic nerve length, 9.92±2.26mm and21.24±2.34mm; ICA length: 9.97±2.20mm and 13.14±2.02mm; OCT width:3.53±0.82mm and 12.65±2.28mm; OCT length: 10.11±2.23mm and 21.74+2.96mm.①optic canal Falcate plica's width: 2.21±0.78mm. The length ofoptic roof, optic floor, medial wail and lateral wall of the optic canal was10.18±1.39mm, 5.65±1.50mm, 11.91±1.80mm, and 8.19±2.46mm, respectively. Themiddle part of the optic canal was the narrowest, and the transverse diameter was4.424-0.53mm, the vertical diameter was 4.32±0.46mm.The axis of the optic canaland middle saggital plane of skull formed an angle of 37.87°±4.68°.The medial wallis the thinnest in the four walls of bony canal. At the cranial end, the ophthalmicartery was located mainly on the inferior medial side (53.3%) and rotated to theinferior lateral side at the orbital end (56.7%).④The medial wall of orbit Thedistance from Dacryon point to anterior ethmoidal foramen and posterior ethmoidalforamen was 17.06±3.56mm, 29.62±3.25mm. The distance from posteriorethmoidal foramen to the middle medial point of the intraorbital opening of the opticcanal was 5.75±1.76mm.⑤sphenoidal sinus The adjacent types of optic canalhad three: the anterior part was homolateral posterior ethmoidal foramen and theposterior part was homolateral sphenoidal sinus, the whole part was homolateralsphenoidal sinus, the whole part was homolateral posterior ethmoidal foramen.On thelateral wall, eminentia internal carotid artery was located in the posteroinferior partand eminentia canalis optica in the anterosuperior part. While eminentia canalisoptica was higher, the bony canal was thinner. The frequency and the averagethickness of the respective segment of eminentia internal carotid artery wererespectively as follow: anterior sella segment 86.7% and 0.594±0.28mm, inferior sellasegment 60.0% and 0.634±0.23mm, posterior sella segment 53.3% and 1.15±0.66mm.⑥The fore-and-aft distance of operative procedure between pterion and theintracranial opening of the optic canal was 46.6±4.6mm and that between Dacryonpoint and eminentia canalis optica was 56.2±4.5mm. Conclusion: Compared bymicroanatorny and clinic, transpterional-sylvian decompression of optic canal was safer and more sufficient to decompress than external transethmo-sphenoiddecompression of optic canal. The middle part of the optic canal was the narrowestand the severest to bind up optic nerve, so opening this part was very critical indecompression of optic canal. Removal of the anterior clinoid process improved theexposure of optic nerve, surrounding structure of ICA and the structure in optic nerve.Moreover, LLAs were all from the interior inferior part of ICA, which should bepayed attention to as we usually could not distinguish them. The true bifurcation waslocated at about limen insulae. Distinguishing actual bifurcution had important clinicsignificance for clipping aneurysm of MCA.
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