Changes in the Ventricular Size During Fractional Pneumoencephalography

Measurements of 40 lateral ventricles, 49 third ventricles, and 46 fourth ventricles were made at different stages during the introduction of air via the lumbar route. Results showed that ventricular air filling during pneumoencephalography is accompanied by ventricular enlargement. The incremental increases were most marked as the initial fractions were introduced and less marked as the later fractions were introduced. It is concluded that the “true” resting size of the ventricles prior to the first fraction of injected air is smaller than the ventricular size commonly recorded at pneumoencephalography. These observations are discussed in relation to basic physical principles involved in ventricular air filling.