Pneumoencephalography (sometimes abbreviated PEG, also referred to as an "air study") was a common medical procedure in which most of the cerebrospinal fluid (CSF) is drained from around the brain by means of a lumbar puncture 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.
Pneumoencephalography was performed extensively throughout the early through mid-20th century. Though it was the single most important way of localizing brain lesions of its time, it was nevertheless extremely painful and was generally not well tolerated by patients. Headaches and severe vomiting were common side effects. During the procedure, the patient's entire body would be spun into different positions in order to allow air to displace the CSF in different areas of the ventricular system and around the brain. This further added to the patient's already heightened level of discomfort. Following the exam, replacement of the drained CSF occurs by slow natural production, and therefore required recovery for as long as 2–3 months before normal fluid volumes were restored. Video of the procedure is documented in a BBC documentary of an early EMI CT installation. . A related procedure is pneumomyelography, where gas is used similarly to investigate the spinal canal.
Despite its overall usefulness, there were still major portions of the brain and other structures of the head that pneumoencephalography was unable to image. This was partially compensated by increased use of angiography as a complementary diagnostic tool, often in an attempt to infer the condition of non-neurovascular pathology from its secondary vascular characteristics. This additional testing was not without risk though, particularly due to the rudimentary catheterization techniques and deleterious contrast agents of the day. Another drawback of pneumoencephalography was that the risk and discomfort it carried meant that repeat studies were generally avoided, thus making it difficult to assess disease progression over time.
Modern imaging techniques such as MRI and CT have rendered pneumoencephalography obsolete. Widespread clinical use of diagnostic tools using these newer technologies began in the mid-to-late 1970s. These revolutionized the field of neuroimaging by not only being able to non-invasively visualize all parts of the brain and its surrounding tissues, but also by doing so in much greater detail than previously available with two-dimensional X-rays. This led to significantly improved patient outcomes while reducing discomfort. Today, pneumoencephalography is limited to the research field and is used under rare circumstances.
Pneumoencephalography appears in popular culture in the movie The Exorcist (1973), when Linda Blair's Regan MacNeil character undergoes the procedure. It is also referred to in Episode 7, Season 7 of House M.D. as an example of a dangerous procedure.
- "Walter Dandy". Walter Dandy. Society of Neurological Surgeons. Retrieved 2011-04-28.
- Greenberg, Mark (2010). Handbook of Neurosurgery. Thieme.