 Pneumocephalus 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 pneumocephalus can occur (similar to what can happen in a tension pneumothorax).CT scans of patients with a tension pneumocephalus 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.