Possible origin of suprasellar arachnoid cysts: neuroimaging and neurosurgical observations in nine cases

Object. In this study the authors identify and investigate two new classifi cations of suprasellar arnchnoid cysts. Methods. The authors used computerized tomography cisternography, magnetic resonance (MR) imaging, and neuroendoscopy to investigate nine cases of sup rasellar arachnoid cysts. A communicating cyst with early filling and early clearance of a radioopaque tracer was found in seven of nine cases; a comm unicating cyst with delayed filling and delayed clearance of the tracer was observed in one case; and a noncommunicating cyst was observed in the othe r. The MR findings indicated a variation in the position of the basilar art ery (BA) bifurcation in relation to the ventral surface of the midbrain. A distance existed between the BA bifurcation and the ventral surface of the midbrain in a communicating cyst with early filling, whereas the BA bifurca tion was posteriorly displaced in a communicating cyst with delayed filling and also in a noncommunicating cyst, leaving little space between the bifu rcation and the ventral surface of the midbrain. Endoscopic observation rev ealed, in the case of communicating cysts with early filling and early clea rance of tracer, that the BA bifurcation is located inside the cyst with no overlying membrane, whereas in a noncommunicating cyst, the BA and its bra nches can be observed through the transparent membrane of the lesion. Conclusions. The authors postulate two different types of suprasellar arach noid cysts: a noncommunicating intra-arachnoid cyst of the diencephalic mem brane of Liliequist and a communicating cyst that is a cystic dilation of t he interpeduncular cistern.