ULTRASTRUCTURE AND PATHOGENESIS OF INTRA-CRANICAL ARACHNOID CYSTS

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  • 1 January 1981
    • journal article
    • review article
    • Vol. 40  (1) , 61-83
Abstract
A detailed light, transmission and scanning electron microscopic study of the arachnoid cyst wall was made in 4 cases and compared with that of the normal arachnoid matter in the human. Reported cases (208) of arachnoid cysts were analyzed to evaluate the anatomical distribution of these lesions and to study their pathogenesis. The structural features of the arachnoid cyst wall that distinguish it from the normal arachnoid membrane are: splitting of the arachnoid membrane at the margin of the cyst, a very thick layer of collagen in the cyst wall: the absence of transversing trabecular processes within the cyst, and the presence of hyperplastic arachnoid cells in the cyst wall, which presumably participate in collagen synthesis. The distribution of arachnoid cysts in 208 reported cases was as follows: sylvian fissure, 49%; cerebellopontine angle, 11%; supracollicular area, 10%; vermis, 9%; sellar and suprasellar area, 9%; interhemispheric fissure, 5%; cerebral convexity, 4%; and the clival and interpeduncular area, 3%. At each site, except possibly on the cerebral convexity, the cyst was associated with a normal subarachnoid cistern. This striking and nearly invariable association of arachnoid cysts with normal subarachnoid cisterns suggests that arachnoid cysts represent a congenital anomaly of the developing subarachnoid cisterns in early intrauterine life. During the process of the complex folding of the primitive neural tube and the formation of normal subarachnoid cisterns, an anomalous splitting of the arachnoid membrane occurs.