Abstract:

Objective　This study aims to investigate the layers of arachnoidal structures and illustrate the relationship between the arachnoid membranes with branches of middle cerebral artery (MCA). The related clinical issues are discussed.   Methods   Six cases of adult cadaveric heads (twelve sides) were dissected under the microscopy. The construction of Sylvain fissure cistern and the different layers of arachnoidal membranes were observed. The course of MCA’s branches and its relationship to the aforementioned membranes were analyzed.    Results    A total of four layers of membranes composed the sylvain fissure cistern. From outer to inner, it was far lateral sylvain arachnoid (FLSa), lateral sylvain arachnoid (LSa), middle sylvain arachnoid (MiSa) and median sylvain arachonid (MeSa) respectively. Among the 12 sides of specimens, four layers  of fully complete and intact membranes were observed in 6 cases. FLSa was always thin with covering among the superior sylvain vein and fusing with the vascular extima. After opening the FLSa, a related thicker membrane named LSa actually served as the lateral wall of sylvain fissure cistern. It existed in all cadavers and separated M3 and M4 segments of MCA. With deeper dissection along the distribution of M3 segment, the outer layer of MiSa was observed to fix artery in the sylvian cistern. A significant inner layer of MiSa was identified around the original part of M3, and divided sylvian cistern into anterior and posterior parts. In 3 cases, this membrane was thinner and cancellous-like in appearance. The deepest layer of membranes was MeSa, which separated M1 and M2 segments. It served as the inner wall of sylvain fissure cistern and lateral wall of internal carotid artery cistern. In five sides of specimens, this membrane was thin and cancellous.   Conclusion    Stratification distribution of sylvain arachnoidal membrane shows close relationship with different segments of MCA. Its individualized contribution might influence the bleeding characteristics of MCA aneurysm.

Key words: Sylvain fissure, Middle cerebral artery, Aneurysm, Anatomy, Neurosurgery