[Long-term follow-up study of the absorption of gas after encephalography in dilated intracranial cerebrospinal fluid spaces (author's transl)].

The absorption of gas after encephalography in different groups of patients was investigated in a long-term follow-up study. Group I (11 patients) showed no pathological findings in the encephalogram. Group II (8 patients) had encephalographic signs of diffuse cerebral atrophy. Group III (7 patients) demonstrated in the encephalogram characteristics of normal pressure hydrocephalus with variously located blocks of air in the subarachnoid space. In group I the gas located in the subarachnoid space had usually disappeared after 24 h, in some cases after 72 h. In group II the pattern of resorption was basically similar, although in one case cortical air could be seen at 96 h. In group III the absorption of air from the subarachnoid space began after 72 h in radiological relevant amounts. In none of the cases of group III could similar short times of resorption be seen in comparison to group I. It is considered that these two groups can be clearly distinguished from each other in the duration of resorption of air from the subarachnoid space. The importance of encephalography as a pathophysiological tool for investigation of both the disturbed resorption and circulation of the cerebrospinal fluid in normal pressure hydrocephalus is stressed.