HE recent emergence of the syndrome of occult hydrocephalus 2~,',1~ has provoked an intensified search for etiologic and pathogenetic factors underlying this entity. From a review of the relevant literature it appeared to us that the villus block merited further exploration. The of obstruction of the cerebrospinal fluid pathway by blockage of the villi has been discussed by many investigators, a1,12,18-21,28 Russell, in 1949,19 stated that retardation of absorption of the cerebrospinal fluid into the venous through the villi is at least a theoretical cause of Ziilch stated that the possibility of a blockage of the by diffuse arachnoidal bleeding . . . has been discussed in the literature, yet anatomical observations do not seem to support the idea. ''~s In 1952 Denny-Brown observed amorphous material plugging the Paccionian Bodies of a patient with infectious polyneuritis and external hydrocephalus. ''7 In 1960, Turner observed blood elements in the arachnoid granulations after death from subarachnoid bleeding. Foltz and Ward 9 and Strain 22 over a decade ago reported examples of symptomatic hydrocephalus as a sequel to subarachnoid hemorrhage. Recently, Hogan and Woolsey 11 reviewed 50 cases of adult hydrocephalus which included 12 attributed to subarachnoid hemorrhage; villus block was once again suggested as a possible cause, but the process was not demonstrated. To determine whether this postulated block might actually be demonstrable, we took advantage of the opportunity to examine particularly the superior sagittal sinus of