E5339. Pneumocephalus: What Else We Should Know
  1. Tseng Chu Chen; China Medical University Hospital
  2. Wu I Ju; China Medical University Hospital
  3. Chou Wei Hsiang; China Medical University Hospital
  4. Wang Tzu Hsiang; China Medical University Hospital
  5. Cheng Kang Lun; China Medical University Hospital
Pneumocephalus is commonly referred to as intracranial gas and includes the presence of gas in any of the intracranial compartments (intraventricular, intraparenchymal, subarachnoid, subdural, and epidural), and it is most frequently present in the frontal lobes. Intracranial air most often results from a craniodural defect, usually postsurgical or traumatic, but it might occasionally be related to infection, iatrogenic, or anesthesia.

Educational Goals / Teaching Points
We share some cases to improve recognition of the CT image pattern of the pneumocephalus and cerebral air emboli. This will also help in differentiating the variant etiology and emergency of the pneumocephalus and cerebral air emboli.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
1. Pneumorrhachis denotes intraspinal air. 2. Pneumocele is a focal or diffuse enlargement of any paranasal sinus (usually frontal) associated with thinning of its bony walls and hyperpneumatization. 3. Pneumosinus dilatans is the same as pneumocele, but the sinus walls are intact and normal. 4. Pneumoventricle is the presence of intraventricular air. 5. Cerebral air emboli is the gas mainly burst into the cerebral vascular system. Among them, tension pneumocephalus and cerebral air emboli are critical and may result in herniation of brain and succedent cerebral infarct. Further management such as surgery or hyperbaric oxygen therapy are required. The mechanism of pneumocephalus could be divided as follows. 1. Ball-valve mechanism: a positive pressure event, such as cough or valsalva maneuver, forces air through the skull defect, which then prevents the air from spontaneously escape. Significant resistance to the outflow of air result in tension pneumocephalus. 2. Inverted bottle theory: excess drainage of CSF leads to a negative ICP gradient, which is relieved by the influx of air. This explains the ventricular shunt procedure or lumbar drain with following low ICP and may trapping of air in the vacuum created inside the cranium.

It is essential to be aware of the etiology of pneumocephalus and cerebral air emboli. Differentiation of a benign or complicated condition and early diagnosis also plays important role and may significantly impact patients’ management and outcome.