[Tension pneumocephalus complicated from bacterial meningitis - a report of case presenting "Mount Fuji sign" in brain CT].

A 39-year-old man was suffered from bacterial meningitis spread from sphenoid sinusitis. During the first several days of the hospitalization, his clinical and laboratory findings were improved by the antibiotics. But he developed impaired consciousness and paraparesis on the sixth hospital day. A CT scan of the brain revealed pneumocephalus with compression of frontal lobes and the widening of the interhemispheric space between the tips of the frontal lobes, which was known as "Mount Fuji sign". Tension pneumocephalus was diagnosed on the basis of the clinical symptoms and the characteristic CT findings. As the bacterial meningitis itself was improving, the surgical treatment was not performed, but the antibiotics therapy continued. He gradually recovered and discharged without any other complications. The mechanism of tension pneumocephalus could not be disclosed. However, it was speculated that tension pneumocephalus was formed due to combined conditions of following factors; the fistula formation between sphenoid sinus and subdural space, the reduced CSF pressure on lumbar puncture, and a ball-valve mechanism though the fistula. We would emphasize that "Mount Fuji sign"on CT or MRI was the important finding to diagnose tension pneumocephalus.