Cerebrospinal fluid turnover and convexity block in mental impairment. A controlled prospective study

A prospective study with a 3-year follow-up was made of 82 patients examined consecutively by pneumoencephalography. Several types of cerebral diseases were represented. The degree of mental impairment was rated. Qauntitative cisternography was performed in 70 of these patients, in which the exponential elimination of injected iodine 131-l human serum albumin from the basal cisterns was calculated. Mental impairment was found to be strongly correlated with a lack of air filling over the parietal convexities and with a slow isotope elimination from the basal cisterns, indicating a slow cerebrospinal fluid turnover. Hydrocephalus was not always present. Only eight had a convexity block for the passage of isotopes.