noun. a diagnostic method utilized from 1918 through the mid-1980s to analyze the cerebral ventricles and subarachnoid space of the brain by administering air into the cerebrospinal fluid. Since the variation in opacity between the brain tissues and air is great enough, the air looks like a dark shadow on the resulting radio-graphic picture, which is acknowledged as a pneumoencephalogram. The growth of computed tomography and magnetic resonance imaging has gotten rid of the necessity for this test though.
PNEUMOENCEPHALOGRAPHY: "Pneumoencephalograpy paved the way for many researchers who discovered the advanced imaging practice methods we use today."