<unk>  is the presence of air or gas within the cranial cavity. It is usually associated with disruption of the skull: after head and facial trauma, tumors of the skull base, after neurosurgery or otorhinolaryngology, and rarely, spontaneously.<unk>  can occur in scuba diving, but is very rare in this context. If there is a valve mechanism which allows air to enter the skull but prevents it from escaping, a tension<unk>  can occur (similar to what can happen in a tension pneumothorax). CT scans of patients with a tension<unk>  typically show air that compresses the frontal lobes of the brain, which results in a tented appearance of the brain in the skull known as the Mount Fuji sign. The name is derived from the resemblance of the brain to Mount Fuji in Japan, a volcano known for its symmetrical cone. In typical cases, there is a symmetrical depression near the midline (such as the crater of a volcano), due to intact bridging veins. Its occurrence seems to be limited to tension<unk>  (not occurring in<unk>  without tension). The sign was first described by a team of Japanese neurosurgeons.<unk>  has also been shown to follow neurosurgical procedures such as deep brain stimulation, where while seemingly innocuous to the patient, may cause brain shift and subsequent stereotactic inaccuracy. Efforts are made by neurosurgeons to reduce<unk>  volume during surgery, and thus, subsequent brain shift.
Pneumocephalus
Hydrocephalus
Cerebrospinal fluid leak
Intraventricular hemorrhage
Acephaly
Pachygyria
Vocal cord hemorrhage
Hemicrania continua