Pneumocephalus — CT Brain (Key Radiological Features)

 

Pneumocephalus — CT Brain (Key Radiological Features)






1. Density
  • Very low attenuation (black)
  • HU ≈ −1000 (air)

2. Typical Locations

  • Subdural (most common)
  • Epidural
  • Intraventricular
  • Intracerebral / intraparenchymal
  • Subarachnoid / cisternal

3. Characteristic Signs

  • Mount Fuji sign (tension pneumocephalus)
    → Separation + compression of frontal lobes by subdural air
  • Air bubble / multiple loculi sign
    → Scattered small air pockets
  • Air-fluid level
    → Suggests CSF leak or communication

4. Mass Effect (if tension)

  • Sulcal effacement
  • Ventricular compression
  • Midline shift
  • Frontal lobe compression

5. Distribution Pattern Clues

  • Non-dependent air (rises anteriorly/superiorly)
  • Often frontal region in supine CT
  • May outline cisterns → “negative contrast effect”

6. Associated Findings

  • Skull base fracture
  • Postoperative changes (craniotomy)
  • Sinus/mastoid air communication
  • CSF leak

One-line clinical correlation

  • Simple pneumocephalus → incidental, small, no mass effect
  • Tension pneumocephalus → neurosurgical emergency (mass effect + Mount Fuji sign)
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