MRI characteristics of cerebral air embolism from a venous source

Cerebral air embolism associated with central venous catheterization often goes unrecognized and can cause major morbidity and mortality.¹ Neurologic findings are nonspecific and include altered consciousness, seizures, and stroke-like symptoms. Additional cardiopulmonary findings are common and include respiratory distress, arrhythmias, and cardiopulmonary arrest.² Brain CT is diagnostic only if obtained immediately because air is rapidly resorbed from the brain arterioles.³ We report two patients who we believe experienced cerebral air embolism originating from a central venous catheter. The patients had remarkably similar patterns of restricted diffusion on brain MRI, which may be characteristic for cerebral air embolism from a venous source.

Case reports.

Case 1.

A 28-year-old woman with systemic lupus erythematosus developed acute renal failure requiring hemodialysis, during which she suddenly developed respiratory distress, right-sided weakness, a right lower quadrantanopia, and left hand clumsiness. A noncontrast brain CT obtained 16 hours after symptom onset was normal, but a MRI with diffusion-weighted imaging (DWI) 6 hours later showed multiple areas of restricted diffusion affecting predominantly cortical areas in bilateral hemispheres (figure, A through D). A MR angiogram (MRA) and a transesophageal echocardiogram (TEE) with injection of agitated saline were normal. Four days later, she again experienced sudden respiratory distress during hemodialysis. A chest CT angiogram showed air in the right heart and right pulmonary artery, but no pulmonary embolism (see figure E-1 on the Neurology Web site at www.neurology.org). Cerebral air embolism due to a defective dialysis catheter was suspected, prompting catheter replacement. Subsequently, the patient’s neurologic status improved, and no further respiratory or neurologic symptoms occurred during 16 months of follow-up.

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Figure. MRI with diffusion-weighted imaging (DWI) obtained 1 day after symptom onset in Case 1 (A through D) and 3 days after symptom onset in Case 2 (E through H). Note the similarity between the DWI sequences of the two patients showing multiple bihemispheric, cortically based areas of restricted diffusion in a gyriform pattern.

Case 2.

Four days after debulking of an intestinal adenocarcinoma, a 58-year-old man developed sudden respiratory distress followed by pulselessness requiring cardiopulmonary resuscitation. His respiratory status improved rapidly, allowing extubation, but he then again developed unexplained respiratory distress, requiring again ventilatory support, followed by a generalized tonic-clonic seizure. He was drowsy and had left-sided weakness and a right gaze preference. Two chest CT angiograms were negative for pulmonary embolism. A noncontrast brain CT was normal, but a brain MRI revealed bilateral areas of restricted diffusion along the cortical gray matter (figure, E through H). MRA, transcranial Doppler ultrasonography, and TEE with IV injection of agitated saline were normal. On further investigation, a left subclavian triple-lumen venous catheter was found to be leaking medication from around its insertion site. After removal of the catheter, no further respiratory or neurologic symptoms occurred during 6 months of follow-up. A follow-up brain MRI 1 week later showed interval normalization of the previously identified areas with restricted diffusion.

Discussion.

We believe that both patients experienced cerebral air embolism as a complication of a central venous catheter. The clinical presentations, the demonstration of air in the right heart and right pulmonary artery in Case 1, the cessation of symptoms after removal of the venous catheters, and the absence of any other embolic source strongly suggest this diagnosis.

When air enters the venous system, air trapping in the heart and lungs can cause poor gas exchange, pulmonary hypertension, arrhythmias, and cardiopulmonary arrest.² Subsequent arterial embolism may result from paradoxical embolism, even in the absence of an intracardiac shunt, as has been reported previously in humans and confirmed in dog models.^4,5 Air is thought to pass from the venous to the arterial circulation either via prepulmonary arteriovenous shunts or by directly crossing the pulmonary capillary bed.⁶

We are aware of a case report that demonstrated DWI changes after cerebral air embolism showing a single localized region of cortical involvement with restricted diffusion.⁷ This patient had a cerebral air embolus due to a tension pneumothorax with chest tube placement. It is unclear whether this patient had a cardiac shunt.⁷ Our two patients had a remarkably similar brain MRI pattern consisting of multiple areas of restricted diffusion along the cortical gray matter in a gyriform pattern involving both cerebral hemispheres. We suspect that the DWI findings caused by cerebral air embolism depend on the size and number of the air emboli. The gyriform pattern seen in our patients may be the result of multiple air emboli that are small enough to be filtered through the pulmonary vasculature and lodge into end-artery territories of the brain, causing ischemia along the cortex.

Cerebral air embolism originating from a venous source often goes unrecognized but should be suspected in patients who have unexplained cardiopulmonary and neurologic findings in the presence of a central venous catheter and the brain DWI pattern described. The absence of an intracardiac shunt does not preclude this diagnosis.