Tension pneumocephalus is a neurosurgical emergency that occurs when subdural air causes a mass-effect over the underlying brain parenchyma, often from a ball-valve mechanism causing one-way entry of air into the subdural space 1.
Tension pneumocephalus has a varied clinical presentation, with reported features including 2:
- severe restlessness
- deteriorating consciousness
- focal neurological deficits
- cardiac arrest.
There are numerous etiologies, including 1-3:
- trauma with leakage of cerebrospinal fluid
- recent neurosurgery (e.g. the complication risk is reported to be 2.5% after chronic subdural hematoma evacuation)
- tumors of the paranasal sinuses
- use of nitrous oxide as an anesthetic agent (NO dissolves into blood and enters the subdural space, expanding the pre-existing gaseous volume)
Irrespective of the mechanism, the increased pressure leads to extra-axial mass effect and compression of the frontal lobes 1,2. The presence of air between the frontal tips suggests that the pressure of the air is at least greater than that of the surface tension of cerebrospinal fluid between the frontal lobes 4.
Initially, subdural air compresses the frontal lobes resulting in the peaking sign is present, before the frontal lobes become separated in a characteristic appearance, aptly termed the Mount Fuji sign 3-5.
An additional reported sign of tension pneumocephalus is the presence of multiple small air bubbles in the subarachnoid space. This has been referred to as the air bubble sign 6 .
These features are, however, not pathognomonic for tension pneumocephalus and can be seen in patients with normal intracranial pressures 7. Regardless of the exact pattern of intracranial gas, clinical deterioration is the key indicator for surgical intervention.
Treatment and prognosis
Tension pneumocephalus is a neurosurgical emergency 2. Treatment is with surgical decompression 2.
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- 2. Pulickal GG, Sitoh YY, Ng WH. Tension pneumocephalus. Singapore medical journal. 55 (3): e46-8. Pubmed
- 3. Heckmann JG, Ganslandt O. Images in clinical medicine. The Mount Fuji sign. The New England journal of medicine. 350 (18): 1881. doi:10.1056/NEJMicm020479 - Pubmed
- 4. Michel SJ. The Mount Fuji sign. Radiology. 2004;232 (2): 449-50. doi:10.1148/radiol.2322021556 - Pubmed citation
- 5. Sinclair AG, Scoffings DJ. Imaging of the post-operative cranium. Radiographics : a review publication of the Radiological Society of North America, Inc. 30 (2): 461-82. doi:10.1148/rg.302095115 - Pubmed
- 6. Ishiwata Y, Fujitsu K, Sekino T, et al. Subdural tension pneumocephalus following surgery for chronic subdural hematoma. J Neurosurg 1988; 68:58–61
- 7. Sebastian B, Moideen J. Mount Fuji is Not as “Active” as We Think. (2018) Indian Journal of Neurosurgery. 77 (11): 880.