Pneumoencephalography

Pneumoencephalography (sometimes abbreviated PEG) was a medical procedure in which most of the cerebrospinal fluid is drained from around the brain and replaced with air, oxygen, or helium to allow the structure of the brain to show up more clearly on an X-ray image. It was derived from ventriculography, an earlier and more primitive method where the air is injected through holes drilled in the skull.