It is a common practice to place epidural or subgaleal drains after craniotomies so as to prevent intracranial and extracranial blood collection . Effective hemostasis and adequate watertight closure of the dura may not necessitate the placement of vacuum drains. Even after proper care taken during the closure, still, pneumocephalus is a common finding postoperatively, though tension pneumocephalus is rare. Pneumocephalus which is common after the evacuation of subdural hematoma can be confirmed with immediate postoperative CT imaging, which usually gets absorbed within a few days.
Dabdoub et al. and Gore et al. termed pneumocephalus and tension pneumocephalus [2, 3]. Pneumocephalus is usually found in the epidural, subarachnoid, intraventricular, intracerebral, and subdural spaces of trauma patients and post-op patients . Tension pneumocephalus is a variant in which air is collected in the subdural space under pressure, and it is a common practice to place epidural or subgaleal drains less than atmospheric pressure probably due to a ball valve-like mechanism. Tension pneumocephalus causes pressure effects and might cause symptoms like lightheadedness, nausea, headache, vomiting, seizures, and hemiparesis [3, 4].
There are instances reporting aphasia, hemiparesis, and cranial nerve compression symptoms. The left hemisphere controls the analytical and language function. In the patients who are right-handed, we could expect that their left hemisphere would be dominant; as a result, language impairment is observed in them. Broca’s area present in the frontal lobe of the dominant hemisphere is usually the left side. The compression of motor neurons present in this area causes aphasia [7, 8]. The CT scan of our patient showed an accumulation of air and compression in the frontal region on the left, explaining this patient’s transient aphasia.
The percentage of oxygen in the atmospheric air is 21%. The normal partial pressure of oxygen (PO2) within the brain tissue ranges from 25 to 36 mmHg. The diffusion of O2 into the brain tissue in case of pneumocephalus is usually large. The brain tissue and blood show higher oxygen content due to its high solubility, and as a result, rapid absorption of oxygen is seen for maintaining the partial pressure within the pneumocephalus, the same as in the surrounding tissue .
As per Gore et al. predictions, in regard to the absorption of intracranial air, the rate of pneumocephalus absorption and FiO2 concentration should always be equal and the rate of absorption should be regulated as per the size of the pneumocephalus .