As more and more experience has been accumulated with flow diversion, we have begun to see unexpected complications, leading to permanent morbidity and mortality. The ipsilateral parenchymal hemorrhage was one of those complications, and we have been unable to fully understand it. We felt that it was important to make the interventional neuroradiology community aware of such a phenomenon so it can be considered in the decision-making process when confronted with an aneurysm that might be treated with flow diversion or suitable for other, more conventional endovascular or surgical techniques.

We have become aware that flow-diverter stents are complex devices that may induce changes in the parent vessel, covered branches, and distal branches that we do not fully comprehend. As such, the use of these devices has been reserved for aneurysms unsuitable for other treatment modalities, or those in which conventional treatments carry high risk, based on careful analysis of experienced neurovascular teams.

We have noticed some resistance to accept this complication as something related to flow diversion effects. We have been confronted with criticism (some more polite and academically oriented than others), particularly for not including the in vitro antiplatelet point-of-care platelet reactivity testing (which is not available in Canada). However, so far, the literature has not provided strong evidence for its routine use, especially when considering hemorrhagic complications. Other criticism (to which we have replied) has questioned our technical skills and suggested these are the reason why our series reported a relatively high rate of this complication (8.5%; 95% CI=2.8-21.3%). In spite of this, the majority of the members of the interventional community we have discussed this with have shown an interest in the phenomenon and provided valuable feedback from their own experiences.

We have planned to do elastography with intra-arterial optical coherence tomography in animal models, comparing the changes in the arterial wall elasticty with the different stents, so as to see if our hypothesis of the

Windkessel effect can be supported. Also, with the ongoing Canadian Experience with Pipeline Embolization Device (initial experience), which includes a greater number of cases and centers, we are getting a better idea of the real incidence of this phenomenon, as well as the clinical implications.  Another potential mechanism for the phenomenon of ipsilateral parenchymal hemorrhage may relate to thromboembolic foreign material (possibly from access tools) depositing in the downstream vessels creating a "susceptible" vascular territory, with the Windkessel effect synergizing and leading to hemorrhage.

These cases have been discussed at the 2011 WFITN meeting, 2012 ASNR meeting, and published in AJNR. We are waiting for more authors to share their experiences. As more data are collected and animal models provide some quantitative values, we may be able to provide better insight and present these new findings at upcoming conferences.

Juan Pablo Cruz and Tom Marotta

Read this article at AJNR.org . . .

 

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