Pneumoencephalography (sometimes abbreviated PEG) is a medical procedure in which cerebrospinal fluid is drained to a small amount 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 picture. It is derived from ventriculography, an earlier and more primitive one where the air is injected through holes drilled in the skull.
The procedure was introduced in 1919 by the American neurosurgeon Walter Dandy.
Pneumoencephalography was performed extensively throughout the late 20th century, but it was extremely painful and, as researchers would later discover, very dangerous. The test was generally not well tolerated by patients. Headaches and severe vomiting were common side effects. Replacement of the spinal fluid was by natural generation and therefore recovery required as long as 2-3 months before full movement was restored. Modern imaging techniques such as MRI and Computed tomography have largely replaced Pneumoencephalography.
By the late 1980s the procedure was largely abandoned by the medical community, having been supplanted by the CT scan and metrizamide cisternography. Today, pneumoencephalography is limited to the research field and is used under rare circumstances. A related procedure is pneumomyelography, where gas is used similarly to investigate the spinal canal.
Pneumoencephalography appears in popular culture in the movie The Exorcist (1973), when Linda Blair's Regan McNeil character undergoes the procedure.