What is the likely cause of trace pneumocephalus and emphysema in the masticator spaces and upper neck on a computed tomography (CT) brain scan?

Likely Cause of Trace Pneumocephalus and Emphysema in Masticator Spaces and Upper Neck

The most likely cause is penetrating trauma or occult skull base/facial fracture with communication between the aerodigestive tract and intracranial/soft tissue spaces, allowing air entry from the upper airway or paranasal sinuses into these compartments. 1

Primary Diagnostic Considerations

Penetrating Neck/Facial Trauma

• Subcutaneous emphysema in the masticator spaces and upper neck is a soft sign of penetrating injury that indicates violation of the aerodigestive tract or airway structures 1
• The combination of pneumocephalus with soft tissue emphysema suggests a communication pathway between the upper airway/paranasal sinuses and both the intracranial space and cervical soft tissues 2
• Even without obvious external wounds, occult penetrating injuries can present with these findings 1

Skull Base or Facial Fractures

• Fractures involving the frontal skull base near the ethmoid roof, cribriform plate, or sphenoid sinus are classic causes of pneumocephalus 3, 4
• Air can track from paranasal sinuses through microfractures or frank fractures into the intracranial space 3, 4
• Concomitant soft tissue emphysema in masticator spaces suggests fractures extending through the facial skeleton 1

Barotrauma Mechanisms

• Increased pressure in the upper airway (from coughing, sneezing, Valsalva maneuvers, or positive pressure ventilation) can force air through existing skull base defects 3, 5
• Mechanical ventilation with high peak inspiratory pressures (>45 cm H₂O) can drive air through occult skull base fractures or defects 3
• Even minor trauma with subsequent forceful sneezing has been documented to cause pneumocephalus through previously undetected fractures 5

Critical Clinical Pitfalls

Do Not Miss These Associated Injuries

• Always evaluate for vascular injury when pneumocephalus and cervical emphysema coexist, as up to 25% of penetrating neck injuries involve vascular structures 1
• Look for signs of aerodigestive tract injury: dysphagia, dysphonia, hemoptysis, or hematemesis 1
• Air bubbling in wounds or active hemorrhage are hard signs requiring immediate surgical exploration without imaging 1

Imaging Algorithm

• CT angiography (CTA) of the head and neck is the first-line imaging study with sensitivity 90-100% for detecting both vascular and aerodigestive injuries 1
• CTA simultaneously identifies the trajectory of air entry, associated fractures, and soft tissue injuries 1
• Plain radiographs may show subcutaneous emphysema and radio-opaque foreign bodies but are insufficient for definitive evaluation 1

Management Priorities

Immediate Assessment

• Determine if patient has "hard signs" (active hemorrhage, expanding hematoma, airway compromise, hemodynamic instability) requiring immediate surgical exploration 1
• If only "soft signs" present (nonexpanding hematoma, subcutaneous emphysema, dysphagia), proceed with CTA before intervention 1
• Assess neurological status for signs of tension pneumocephalus: altered mental status, fixed dilated pupils, or focal deficits 3

Conservative vs. Surgical Management

• Most cases of traumatic pneumocephalus resolve with conservative management: 100% oxygen therapy, head elevation, avoidance of Valsalva maneuvers, and observation 4, 2
• Surgical intervention is indicated for: tension pneumocephalus (Mount Fuji sign on CT), progressive neurological deterioration, or identification of surgically correctable skull base defects 3, 4
• Antibiotic prophylaxis should be considered given the communication between contaminated spaces (sinuses, oropharynx) and sterile intracranial compartment 2

Follow-up Imaging

• Repeat CT in 24-72 hours to document resolution or progression of pneumocephalus 2, 5
• Persistent or worsening pneumocephalus suggests ongoing air leak requiring surgical repair 4

Less Common Etiologies to Consider

• Iatrogenic causes: recent neurosurgery, lumbar puncture, or epidural procedures 4
• Spontaneous pneumocephalus: extremely rare, associated with skull base tumors or chronic sinusitis with bony erosion 4
• Cerebral air embolism: presents with pneumocephalus but requires pulmonary source (ruptured bulla, barotrauma) and is associated with acute cardiopulmonary events 6