Background
A 65-year-old man presented with headache after a minor head injury (slip and fall
with head lightly hitting a chair). Computed tomography (CT) revealed pneumocephalus
with Mount Fuji sign. The possibility of tension pneumothorax was suspected. Because
the patient did not have any signs of raised intracranial tension (ICT), after his
proper counseling, surgery was withheld. In addition to this, the patient was not
willing for any procedures; hence he was kept under observation. Repeat CT after 3
days and 1 week showed a progressive reduction in extra-axial air. Neurologic status
of the patient remained stable, and he was discharged.
Imaging Findings
Plain CT of the brain showed extra-axial accumulation of air that is predominantly
seen in the prefrontal subdural space, interhemispheric and sylvian fissures, and
basal cisterns. Air in the interhemispheric fissure causing separation of the cerebral
hemispheres with a heaped-up appearance of the frontal lobes showed the characteristic
Mount Fuji sign ([Fig. 1]). No obvious fractures were visualized in the cranium. Follow-up CT of the brain
after 3 and 7 days ([Fig. 2]) showed reduction in pneumocephalus with subdural cerebrospinal fluid (CSF) density
fluid.
Fig. 1 Nonenhanced computed tomography axial sections of brain showing “Mount Fuji sign.”
Air noted in bilateral frontal subdural space and interhemispheric fissure (arrows).
Also seen “air bubble sign” (arrowhead) in the left sylvian fissure.
Fig. 2 Follow-up computed tomography axial sections of brain after 7 days showing reduction
in subdural and interhemispheric air and minimal subdural hygroma (arrow).
Discussion
Mount Fuji sign is widely regarded as a radiologic sign of tension pneumocephalus,[1] a neurosurgical emergency. It is documented as a useful sign to differentiate between
tension and nontension pneumocephalus.[1]
[2] Presence of air in the interhemispheric space between the frontal lobes is considered
as a sign of raised ICT, with air pressure at least greater than the CSF pressure.[2] In spite of all these features, fortunately our patient did not show any signs of
raised ICT and was managed conservatively. In the literature, all the cases reporting
Mount Fuji sign, due to various causes, have been managed neurosurgically to relieve
the raised ICT.[3]
[4] To the best of our knowledge, this is the first reported case of the patient with
Mount Fuji sign on CT of the brain and was managed conservatively. Also, the case
demonstrates that Mount Fuji sign can be seen in nontension pneumothorax that can
even be due to trivial trauma to the head. Again, it proves the famous saying by William
Osler: “Medicine is a science of uncertainty and an art of probability.”[5] Nothing in medicine comes without exceptions. Contrary to the popular belief at
least among residents and young radiologists, one should always consider the neurologic
condition of the patient before the diagnosis of tension pneumocephalus based on Mount
Fuji sign.
Age-related diffuse brain atrophy and volume loss could be the possible reason that
helped our patient tide over the pneumocephalus and remain asymptomatic. All cases
should be evaluated based on clinical features along with radiologic appearance and
then only be considered for conservative management with close monitoring.
