Tension pneumocephalus occurs with subdural air causing mass effect over the underlying brain parenchyma, often from a ball valve mechanism causing one way entry of air into the subdural space1.
Tension pneumocephalus can be a neurosurgical emergency.
- dehiscence in the skull base or calvaria, such that the egress of air is blocked by an obstruction.
- nitrous oxide, which was used as an anaesthetic, diffused into air-filled spaces and expanded the gaseous volume.
Irrespective of the mechanism, the increased pressure lead to extra-axial mass effect and compression of the frontal lobes. 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 lobes2.
On CT, compression of bilateral frontal lobes with separation of the tips due to air is named the Mount Fuji sign.
Treatment and prognosis
Tension pneumocephalus is a neurosurgical emergency. Treatment is with surgical decompression.