Chronic fibrotic or adhesive changes in the spinal arachnoid have been described for more than forty years. Designated as meningitis, or more often as arachnoiditis, these changes have been characterized as serous, fibrous, adhesive or cystic and as diffuse, disseminated or circumscribed. The first report was that of Schwarz,1who in 1897 described the clinical and pathologic features in a case supposedly of syphilitic origin, with sclerotic and cystic meninges and focal areas of softening and cavitation in the spinal cord. Schwarz's article is one of the few containing detailed pathologic descriptions and has never received the attention it deserves. Circumscribed cysts of the arachnoid are especially apt to simulate tumors, as shown in the first report from America, in 1903, by Spiller.2Numerous later reports, such as those by Horsley,3Munro,4Schuster,5Mauss and Krüger,6Stookey,7Barré,8Elkington,9and Selinsky