ABSTRACT
Objective To explore the anatomy for transethmoidal-sphenoid optic nerve decompression under endoscopy and its significance in operation. Methods Fifteen cases (30 sides) of formalin-fixed adult optic canal specimens were dissected under the microscope. The anatomic characteristics of the optic canal and its adjacent were observed, and the relative parameters were evaluated according to nasal endoscopic approach. Results ①The relationship between the optic carotid triangle(OCT)with the optic canal, the ophthalmic artery, the cavernous sinus and the internal carotid artery were invariable, its present ratio were in 66.7%. ②The mean distance from the front margin of nasal columella floor to medial wall of the orbital opening, middle portion and the cranial opening in the optic canal were (72.79 ± 5.40)mm, (75.85 ± 5.10)mm and (79.34 ± 4.95)mm, respectively, and the elevation angles were (39.45 ± 3.68)°, (37.30±4.24)°and (35.45 ± 4.16)°, respectively. ③The mean thickness of sheath in the medial wall of the orbital opening,middle portion and the cranial opening were (0.70 ± 0. 18)mm, (0.51 ± 0.15)mm and (0.49-0.22)mm,respectively. The difference in thickness between the orbital opening and middle portion, the cranial opening were very remarkable(P ＜ 0.01 ). ④The lateral deviate distance from medial wall of the orbital opening, middle portion and cranial opening to sagittal median plane of cadaveric were 1/2 (12.69 ± 2.73)mm、1/2( 19.61± 3.47)mm and 1/2 (25.79 ± 3.23)mm, respectively. Conclusion OCT is the most reliable anatomic landmark to locate the optic canal, and the key point is at the orbital opening of the optic nerve in the optic nerve decompression. It is secure and feasible to cut the sheath from the place where the medial wall crosses the superior wall of the optic nerve.
ABSTRACT
There have been known two routes in pterional approach to the distal basilar artery aneurysms : one is via the space between the optic nerve and internal carotid artery(optic-carotid triangle: OCT) and the other is lateral to the ICA(retrocarotid approach : RCA). Although the approach via OCT has several advantages of its own, it had been considered to be used in a very limitted cases. Since we successfully clipped the aneurysms via OCT in 4 cases out of 12(33%), neuroradiological findings observed in these 4 cases are analyzed and reported. Measurement were made in the following items on the cartoid angiogram of the cases operated via OCT(OCT group) and RCA(RCA group) : the distance of ICA bifurcation from midline(D), height of ICA bifurcation from the base line between anterior and posterior clinoid process(H). Although these two values seemed to be higher in OCT group than those in RCA group, no significant difference was found. The product of D and H(D x H) was observed to be significantly higher in OCT group than in RCA group. The value of DxH is considered one of the indicaters of the size of OCT and is proved to be useful to judge whether approach via OCT is applicable or not. The approach via OCT has several such advantages as no injury to the occulomotor nerve, less retraction to ICA and easy visualization of p1 segment of the opposite side. The space of OCT can be used not only for clipping itself but also as a line of sight to the deep structures as well as clip applied from other routes.