Pneumocephalus, pneumoencephalus, intracranial pneumatocele or aerocele are all terms for air in the head, where it is not meant to be. It can be a normal consequence of brain surgery and is usually not a major thing, except were there is too much air, or when it ends up under tension. This condition has never come up in the exam until a relatively recent radiology question (Question 14.2 from the first paper of 2016). The college presented us with a CT slice depicting the classical "Mount Fuji" sign, in a patient who has lost consciousness following a C5-6 epidural abscess drainage.
To answer the question "what would it be like to have a lot of air around my brain", Markham (1967) performed a survey of around 300 patient cases. The patients had the following symptoms:
In addition to these, one might expect tension pneumocephalus to present with all the characteristic features of increased intracranial pressure.
The list below is copied directly from Schirmer et al (2010)
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Other causes of pneumocephalus not mentioned above may include:
This image, used for Question 14.2 from the first paper of 2016, was stolen shamelessly from Eric Miller's Emergency Medical Minute (Podcast #93). Specifically, it is tension subdural pneumoencephaly, which can be identified by the "Mount Fuji" sign (S.Michel, 2004). Observe how the intracranial air is under pressure: the frontal lobes have been squished and separated, giving a twin peak appearance. The lateral venticle is somewhat squashed-looking, which also suggests that there is increased intracranial pressure.
Tension pneumoencephalus is a situation where air is able to enter the skull, but not exit it. This occurs when some sort of a valve-like mechanism is formed. This is called the "ball-valve" or the "inverted bottle" mechanisms.
The ball-valve effect is where air enters the cranial cavity through a defect when it is forced there under prssure (eg. coughing, sneezing etc.). Then, it cannot passively escape (the pressure is not great enough).
The inverted bottle effect is due to CSF drainage, and is the most likely explanation for tension pneumocephalus following spinal surgery. It is also the most likely mechanism to explain the pathology in Question 14.2 from the first paper of 2016. Lundsford et al described this in 1979. In essence, the drainage of CSF from the spine creates a negative intracranial pressure, which entrains air. " The mechanism for entry of air into the intracranial compartment is analogous to the entry of air into an inverted soda-pop bottle", the authors muse. "As the fluid pours out, air bubbles to the top of the container".
This is well covered in the excellent free article by Dabdoub et al (2015), the salient features of which are summarised below.
In summary, these are the management options:
Nelson, A. S., et al. "Pneumoencephaly following lumbar puncture in association with an ethmoidal osteoma and porencephalic cyst." Journal of Neurology, Neurosurgery & Psychiatry 78.10 (2007): 1149-1151.
Michel, Steven J. "The Mount Fuji Sign 1." Radiology 232.2 (2004): 449-450.
Turgut, Mehmet, and Orhan Akyüz. "Symptomatic tension pneumocephalus: an unusual post-operative complication of posterior spinal surgery." Journal of clinical neuroscience 14.7 (2007): 666-668.
Schirmer, Clemens M., Carl B. Heilman, and Anish Bhardwaj. "Pneumocephalus: case illustrations and review." Neurocritical care 13.1 (2010): 152-158.
Satapathy, G. C., and H. H. Dash. "Tension pneumocephalus after neurosurgery in the supine position." British journal of anaesthesia 84.1 (2000): 115-117.
Markham, J. W. "The clinical features of pneumocephalus based upon a survey of 284 cases with report of 11 additional cases." Acta neurochirurgica 16.1-2 (1967): 1-78.
Lunsford, L. Dade, et al. "Subdural tension pneumocephalos: Report of two cases." Journal of neurosurgery 50.4 (1979): 525-527.
Dabdoub, Carlos B., et al. "Review of the management of pneumocephalus." Surgical neurology international 6 (2015).
Karavelioglu, Ergun, Olcay Eser, and Alpay Haktanir. "Pneumocephalus and pneumorrhachis after spinal surgery: Case report and review of the literature." Neurologia medico-chirurgica 54.5 (2014): 405-407.
Gore, Pankaj A., et al. "Normobaric oxygen therapy strategies in the treatment of postcraniotomy pneumocephalus." (2008). Journal of Neurosurgery May 2008 / Vol. 108 / No. 5 / Pages 926-929
Paiva, Wellingson Silva, et al. "Effects of hyperbaric oxygenation therapy on symptomatic pneumocephalus." Therapeutics and clinical risk management 10 (2014): 769.
Donovan, Daniel J., et al. "Aeromedical evacuation of patients with pneumocephalus: outcomes in 21 cases." Aviation, space, and environmental medicine 79.1 (2008): 30-35.
Dabdoub, Carlos B., et al. "Review of the management of pneumocephalus." Surgical neurology international 6 (2015).
Viswanathan, Rajanandhan, Venkatesan Sanjeevi, and Balasubramanian Dhandapani. "Unusual and Rare Pneumocephalus Presentations in a Tertiary Care Center: Management Strategies and Review of Literature." Indian Journal of Neurosurgery 9.01 (2020): 42-48.