Is pneumocephalus visible on a head computed tomography (CT) scan without contrast?

Pneumocephalus Detection on Non-Contrast Head CT

Yes, pneumocephalus is readily visible on head CT without contrast. Air appears as hypodense (black) areas within the cranial cavity on CT imaging, creating a distinctive appearance that is easily identifiable without the need for contrast enhancement 1.

Imaging Characteristics of Pneumocephalus on Non-Contrast Head CT

• Air appears as hypodense (black) areas with Hounsfield units of approximately -1000, creating high contrast against brain tissue (+20 to +45 HU) and cerebrospinal fluid (0 to +15 HU)
• Location can vary depending on etiology:
  • Subdural spaces
  • Subarachnoid spaces
  • Intraventricular spaces
  • Intraparenchymal areas

Clinical Context and Etiology

Pneumocephalus is most commonly associated with:

1. Traumatic causes - skull fractures, especially those involving paranasal sinuses or mastoid air cells 2
2. Iatrogenic causes - neurosurgical procedures, spinal surgeries 3, 4, 5
3. Infectious causes - gas-forming bacterial infections (rare) 6
4. Spontaneous causes - rare, may occur with sneezing or other Valsalva maneuvers in patients with existing skull defects 2

Diagnostic Algorithm

When pneumocephalus is suspected:

1. First-line imaging: Non-contrast head CT

   • Rapid acquisition
   • High sensitivity for detecting intracranial air
   • Can simultaneously evaluate for other pathologies (fractures, hemorrhage)

2. Follow-up imaging (if needed):

   • Repeat non-contrast head CT to monitor resolution
   • Consider CT with thin-slice technique through skull base if source is unclear
   • MRI may be considered for evaluating associated complications or underlying causes

Clinical Significance and Management Implications

The detection of pneumocephalus should prompt:

• Identification of the source of air entry
• Evaluation for associated cerebrospinal fluid leak
• Assessment for signs of tension pneumocephalus (mass effect)
• Appropriate management based on cause and severity

Common Pitfalls to Avoid

• Misinterpretation: Don't confuse pneumocephalus with normal air-containing structures (paranasal sinuses, mastoid air cells)
• Incomplete evaluation: Always assess for underlying skull fractures or CSF leaks when pneumocephalus is identified
• Delayed diagnosis: In post-surgical or post-traumatic patients with new neurological symptoms, consider pneumocephalus even if initial imaging was negative 5

According to the ACR Appropriateness Criteria for altered mental status, non-contrast head CT is the first-line imaging test for evaluating suspected progressive intracranial complications, including pneumocephalus 1. This modality provides rapid assessment and can effectively detect air within the cranial cavity without the need for contrast enhancement.