Arachnoid membrane: the first and probably the last piece of the roadmap.

Most neurosurgical procedures could be performed noninvasively by working through the natural corridors provided by the subarachnoid cisterns. In consequence, the subarachnoid cisterns have been considered as the roadmaps for the microneurosurgeons. The concept and the contents of the cisterns have been well known and described, but the knowledge of the detailed anatomy of the arachnoid membranes, which are the real septa of the cisterns and provide the practical and important landmarks and planes for the dissections during the brain surgeries, is still lacking. The present article reviews the previous reports of the intracranial arachnoid membranes with a special emphasis on the microsurgical anatomy and the clinical significance.