A triad of airencephalographic findings in patients with mental impairment: a controlled prospective study.

A controlled prospective study of 82 patients examined consecutively during one year by airencephalography was made. Care was taken to excude bias and to assess observer error. A close correlation was found between mental impairment (as a sign of "organic brain syndrome", resulting from various cerebral diseases), and three airencephalographic findings, namely 1) lack of air filling over the parietal convexities (parietal air block), 2) widening of the lateral and third ventricles and 3) widening of the Sylvian and interhemispheric fissures. Of these, parietal air block was found to be the most sensitive sign. In addition to the patients with normal-pressure hydrocephalus, the majority of patients with presenile dementia and alcoholic encephalopathy had parietal air block. The results are in agreement with those reported in an earlier retrospective study. Leptomeningeal changes may account for the finding of parietal air block in certain patients, but in the majority of cases there is no complete obstruction of the subarachnoid space, as judged from the results of isotope cisternography. Organic changes in the brain and leptomeninges may create special physical conditions for the appearance of convexity air block at airencephalography. Recognition of convexity air blocks seems to have considerable diagnostic and therapeutic implications, since it contributes appreciably to the judgment whether a patient's condition is basically determined by an organic brain syndrome or constitutes a functional mental disorder. The possible pathophysiological association between mental impairment and parietal air block warrants attention.