The CT scan in this Teaching NeuroImage1 proves the presence of air in the cavernous sinus. The most plausible explanation for this is a retrograde venous air embolism from the port-a-catheter with the patient in a vertical position. Retrograde venous cerebral embolism may lead to focal or generalized venous congestion, venous brain infarction, or even death. It is not credible that paradoxical arterial air emboli would have coalesced in the cavernous sinus after passing through brain capillaries.
Whether the acute clinical picture in this case can be explained by retrograde venous cerebral air embolism remains unclear. Theoretically, in this patient both paradoxical (antegrade) arterial air and (retrograde) venous air embolism may have occurred. If this were the case, the CT image only illustrates the venous part of the story. Unimaged arterial air may have led to a small but strategic lacunar lesion (e.g., in the internal capsule) that was not visualized on diffusion-weighted MRI.
Author Response
Coebergh et al. agree that the most plausible mechanism for air in the cavernous sinus is a retrograde venous embolism. In reviewing our article, we concur that the discussion may be misleading; we used the term TIA to denote a clinical syndrome which resolved within 1 hour rather than to referring to a proposed mechanism.
We know that the patient was sitting upright at the time. Because air is less dense than blood, it is possible that the embolism traveled retrogradely to produce the transient symptoms. On review of the catheter placement seen on chest x-ray at time of admission, the line appears to be placed with the tip in the superior vena cava. We refer to a study2 that monitored paradoxical emboli in patients with transatrial shunts after central line placements. The head CT shows presence of air in the sinus and makes it more likely that it was retrograde. However, paradoxical air embolism should always be considered in patients with transatrial shunts. We thank Coebergh et al. for raising this important issue.
References
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