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Air fat embolism

Cerebral air embolism is a rare but potentially fatal condition that can occur iatrogenically during vascular procedures, central venous catheter placement, cardiac surgery, or through paradoxical embolism via a patent foramen ovale. Clinical presentation includes confusion, motor weakness, decreased consciousness, seizure, and loss of vision.

Causes

Iatrogenic/medical procedures are the most common cause, including cardiothoracic and aortic surgery, extracorporeal circulation and mechanical circulatory support, catheter-based cardiac interventions, neurosurgery, lung biopsy, interventional radiology, and — very commonly — insertion or especially removal of central venous catheters.

Diving/barotrauma: rupture of alveolar–capillary membranes as trapped compressed gas expands during ascent allows air into the pulmonary veins and thence to the cerebral arteries; this can occur from depths as shallow as 1 m.

Trauma, decompression sickness, and other barotrauma; bubble composition may be air, nitrogen, or carbon dioxide.

Pathophysiology

Bubbles cause mechanical arterial occlusion, ischemia, and infarction. Small bubbles may be rapidly reabsorbed with resolution of symptoms; large bubbles can take hours to absorb, sustaining ischemia below the threshold for neuronal survival.

Beyond obstruction, gas emboli cause endothelial/vascular injury, vasospasm, thromboinflammation, oxidative stress, and plasma leak, a secondary injury cascade resembling that of ischemic stroke.

Key Images

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Fatal

Image

Look For First
  • Gas/air within cerebral arteries or right ventricle on CT with lung window optimization
  • Acute ischemic stroke in watershed distribution on MRI DWI or CT
  • Empty right ventricle with air in right atrium (if large venous air entry)
  • History of recent instrumentation or vascular procedure
Key Image Findings
  • CT in acute setting may show hypodense gas bubbles within cerebral arteries or cardiac chambers; air is rapidly absorbed so imaging must be performed acutely.
  • Lung window settings on CT significantly improve detection of small air emboli compared to standard brain windows.
  • MRI is insensitive for direct visualization of air but shows T2/DWI hyperintense acute ischemic infarction often in watershed distribution patterns.
  • Air emboli in venous circulation may collect in the right ventricle creating a blood-air froth that impairs cardiac output.
  • Paradoxical embolism through patent foramen ovale (present in ~35% of autopsies) allows venous air to reach cerebral circulation.
  • Cerebral edema and mass effect may develop secondary to acute ischemic stroke from arterial occlusion.
  • Small air bubbles occlude distal cerebral arteries causing end-artery distribution infarcts rather than embolic shower pattern.
  • Fatal air embolism historically involves 100-300 mL of air entering systemic or coronary circulation.
Differential Diagnosis
  • Pneumocephalus: air in intracranial compartment but typically located in subdural space or ventricles following head trauma or skull base surgery, not within cerebral vessels or as acute emboli.
  • Thrombotic stroke: causes similar acute DWI hyperintense ischemic pattern but lacks visible gas on CT and has different etiologic context without instrumentation history.
  • Fat embolism: produces similar clinical presentation and stroke pattern but fat is not visible as gas on imaging and has different clinical setting (long bone fracture, orthopedic surgery).
  • Fat in dural sinuses: can mimic air in dural venous sinuses but typically follows fat embolism syndrome and shows different imaging characteristics.
  • Arterial dissection: causes acute ischemic stroke but imaging shows arterial wall abnormality rather than intravascular gas.
  • Cardioembolic stroke from atrial fibrillation: produces acute ischemic stroke pattern but lacks acute gas visualization and different risk factor profile.
Discussion

Cerebral air embolism is frequently missed and underreported, with many cases only identified post-mortem or after significant neurological deterioration, especially in patients with central venous catheters or undergoing vascular procedures.

Air enters circulation when there is access to a vessel combined with a pressure gradient favoring entry; paradoxical embolism through patent foramen ovale converts venous air sources to arterial/cerebral distribution.

Large venous air volumes collect in the right ventricle where the pumping action creates blood-air froth; because air is compressible, this causes acute circulatory failure and potential cardiac arrest.

Clinical presentation is non-specific (confusion, weakness, decreased consciousness, seizure, vision loss) making diagnosis challenging without high clinical suspicion and appropriate imaging technique.

Acute ischemic stroke from air embolism often follows a watershed distribution pattern rather than single arterial territory, reflecting hemodynamic mechanism of injury.

Increasing evidence supports hyperbaric oxygen therapy to accelerate air resorption, making early recognition critical for treatment initiation within appropriate time window.

Reporting Pearls

When reporting cerebral air embolism, specify the location and extent of intravascular gas (e.g., "hypodense gas bubbles within the middle cerebral artery distribution"), note any associated acute ischemic stroke on DWI/ADC, and explicitly mention whether imaging was performed acutely (when gas is visible) versus delayed (when only infarction is evident); always recommend lung window review on CT for optimal sensitivity.

Pitfalls
  • Failure to use lung window settings on CT severely reduces sensitivity for detecting small air emboli; standard brain windows may miss hypodense gas.
  • Delayed imaging (hours after event) may show only acute infarction without visible air, as gas is rapidly absorbed, leading to misdiagnosis as primary stroke.
  • Mistaking pneumocephalus (air in subdural space or ventricles from trauma/surgery) for cerebral air embolism; the key distinction is intravascular location of emboli versus extravascular collections.
  • Attributing acute neurological deterioration to procedural stroke without considering air embolism in patients with recent central venous catheter placement, cardiac surgery, or lung biopsy.
Source: Reference source

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