The Study Of Microsurgical Anatomy And Related Operative Approach Of The Basilar Artery

Objectives:1. To study the microsurgery variation characteristics of the basilar artery(BA) and main branches; make clear the neighbouring strucural relationships between the BA and the adjacent crinial bones and nerves,and their blood-supply as well; and therefore provide anatomical data for relevant clinical operations in this area such as the aneursym clipping operation, cerebellar tumor operation, and the intervention operation.2. To explore the scope of the bifurcation of basilar artery and compare difference of these operative approaches via pterional approach and subtemporal approach, and provide reference for the microsurgery of BA apex aneurysm.Methods:Ten (20 sides) adult cadaveric specimens which perfused with colored silicone were studied by using the subtemporal approach and pterional approach under the microscope, respectively. Firstly, we observed and measured the relationsh-ip among the important neurovascular structures, and described the exposure scope of the bifurcation of basilar artery and compared difference of related operative approaches. Then, cleaning the cerebrum, we measured the length, diameter and number of the BA branches; as well as recorded.their shapes, courses, perforating branches and connections.Results:l.The diameter of the BA varied from 2.9-5.4mm (mean±standard deviation: 4.25±0.67mm). The mean length of BA was 26.40±4.35mm. The mean number of perforators on two sides arising from the BA was 4.0±1.06.2.The diameter size of the AICA ranged between 0.47 and 2.36 mm(mean±standard deviation:1.15±0.43mm),5% of the total ACIAs originated from the upper segment of the (BA),20% from the middle segment, and 75% from the lower segment. The incidence of AICA formed the loop of AICA near facial root was 80%.3. The SCA arose very close to the basilar bifurcation in our series-1 to 4 mm from the basilar artery bifurcation (mean±standard deviation:1.52±0.38mm). The diameter of the SCA varied from 0.4 mm to 2.6 mm (mean±standard deviation:1.35 ±0.38mm). In the study the nearest blood vessel to the trigeminal nerve was the SCA, with a distance of 0-8.2mm (mean:2.17±0.45mm).4.The mean diameter size of the PCA was 2.23±0.17mm. On an average three to seven small perforators (mean 4.2±1.1) were seen to arise from either P1 segment.5.There were three BA bifurcation above the posterior clinoid process(PCP) which were up to 12.25mm; Five example located equal level with PCP. There were two example below PCP which were low to 8.24mm.6.The pterional approach can provide excellent exposure for the posterior part of the sellar region and BA bifurcation via optic nerve-ICA space (spaceⅡ) under the angle 30°. SpaceⅢwas between ICA and free edge of tentorium of cerebellum.The visibility of the interior side was more and more bigger, but the lateral side was blocked by temporalis lobe in spaceⅢunder different visual angles from 0°to 60°, and the area of spaceⅢunder angle 45°was the biggest. By drilling the PCP, the exposure of superior 1/3 segment of the basilar arterycan be increased.7.The shortest distances from the zygomatic arch to the edge of tentorium incisura was 39.24±1.27mm. We found that the trochlear nerve entered the edge of tentorium in post-lateral PCP. The mean distance was 15.72±3.81mm. The subtemporal approach can provide wide exposure for the base of the middle cranial fassa and perforating arteries arising from BA bifurcation and P1 segment. The exposure of the BA apex can be increased after cutting tentorium, and a wider scope of expoure was obtained to the lateral aspect of the brainstem.Conclusions:1. Significant microanatomical variations were found in the BA and main bran-ches which were closely related to the adjacent important neural structures. It is important for neurosurgeons to understand the microsurgical anatomy of the basilar vessels in order to treat pathologies in this area safely and confidently.2. Compared with spaceⅡ, exposure of spaceⅢhad great advantage when dealing with the BA apex aneurysms which were higher than PCP via pterional approach. We should pay attention to the protection of oculomotor nerve. By drilling the PCP, the exposure of superior 1/3 segment of the basilar arterycan be increased.3. The subtemporal approach has advantages such as shorter distance of operation, bigger straight visual angle. We can observe the perforating branches arising from BA bifurcation and P1 segment though lateral wider visual field, when clipping the aneurysm which directed backward. Cutting the tentorium at the post-lateral 17mm point away from PCP can avoid damaging the trochlear nerve.4. The microsurgery for BA apex aneurysms in the posterior circulation is very difficult and the key to the successful operation is to expose the aneurysms fully by the appropriate approach. So we should analyze carefully the relationship between BA bifurcation and the PCP, as well as location,the growth direction of the aneurysm though imaging examination (DSA, CTA) before operation.