• Kohei Inoue, Askin Seker, Shigeyuki Osawa, Luis Felipe Alencastro, Toshio Matsushima, and Albert L Rhoton.
• Department of Neurosurgery, University of Florida, Gainesville, Florida 32610, USA.
• Neurosurgery. 2009 Oct 1; 65 (4): 644-64; discussion 665.

ObjectiveA limitation of previous studies of the arachnoid cisterns and membranes is that the act of opening the sylvian and interhemispheric fissures and basal arachnoid often led to destruction of the cisternal compartments and their membranous walls. The goal of this study was to overcome this limitation by combining the surgical microscope and endoscope for the examination of the cisternal compartments and their membranous walls.MethodsThe supratentorial cisterns were examined in 22 cadaveric brains using both the operating microscope and the endoscope.ResultsThere are 2 types of arachnoid membranes: outer and inner. The outer arachnoidal membrane surrounds the whole brain, and the inner membranes divide the subarachnoid space into cisterns. Twelve inner arachnoid membranes were identified in the supratentorial area: diencephalic, mesencephalic, medial carotid, intracarotid, intracrural, olfactory, medial and lateral lamina terminalis, and proximal, medial, intermediate, and lateral sylvian membranes. These membranes partially or completely separate the subarachnoid space into 9 supratentorial cisterns: sylvian, carotid, chiasmatic, lamina terminalis, pericallosal, crural, ambient, oculomotor, and interpeduncular. There is a confluent area between the carotid, interpeduncular, and crural cisterns, which frequently has no membrane separating these cisterns.ConclusionTwelve inner arachnoid membranes and 9 cisterns were identified in this study.

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