A 52 y.o. woman presents with altered mental status

She had complained of a headache according to her husband.

What do you see on the head CT?

Our patient had pneumocephalus; air within the cranial cavity.  In the case of our patient a middle ear infection had progressed to mastoiditis and erosion through the dura into the cranial cavity.  Meningitis also occurred and a culture grew out Pneumococcus.  Purulent material was draining from the R ear.

Lecat   was the first to find air within the cranial cavity in 1741.  The name Pneumocephalus was coined in 1884 by Chiari.  

CAUSES OF PNEUMOCEPHALUS

Trauma- Most causes of pneumocephalus are due to trauma or surgery. Trauma accounts for 75% of the cases. In these cases a ball valve effect can occur with a tear in the dural acting as a valve allowing air to enter but preventing outflow. A vacuum effect is also thought to occur as in the case of a CSF leak where  CSF leaking out may create a vacuum and  draw air into the intracranial space.

This pt had lung cancer with erosion into the airway during hiccuping he developed a fatal air embolus.

Injected air- an air embolus can occur from inadvertent injection while starting an IV or doing an LP. Nitrous oxide inhalation and barotrauma from diving , sneezing and Valsalva can also cause it.

Airline flights- Boyles law states  when pressure and volume are inversely proportional . When the pressure decreased in the cranial cavity the  volume of air increases.  This explains why pneumocephalus increases during airline flights. Tension pneumocephalus has been reported on an airline flight after a cervical epidural injection.

Boyles law: as the pressure increases the volume decreases

https://en.wikipedia.org/wiki/Boyle%27s_law#/media/File:Boyles_Law_animated.gif

Infection-the middle ear is the most likely source of infection causing pneumocephalus.

Tumors-Tumors, especially at the base of the skull can allow air to enter the supratentorial space.

While 85% of cases of pneumocephalus resolve spontaneously in one week; the rest may go on to develop “tension pneumocephalus” which is life-threatening.  The classic Mount Fuji sign develops prior to the increased pressure causing brain herniation.

Mt. Fuji sign

Our patient underwent a tube placement through the TM on the R and is awaiting a definitive surgery.

Smilowska K, Sznajder-Stacha K, Kocylowski D, et al. Pneumocephalus as a rare complication: a systematicreview plus clinical vignette. Polish Journal of Neurology and Neurosurgery 2021, Vol 55(3) 253-258.

Baba M, Tarar O, Syed A. A rare cawe of spontaneous pneumocephalus associated with nontraumatic cerebrospinal fluid leak. Case Rep Neuro Med. 2016;2016:1828461.

Chiari H, A case of accumulation of air in the ventricles of human brain. Zeitschrift fur Heilkunde, vol 5,PP384-390, 1884.