Original ArticleCan the Windkessel Hypothesis Explain Delayed Intraparenchymal Haemorrhage After Flow Diversion? A Case Report and Model-Based Analysis of Possible Mechanisms
Introduction
Recently, several reports have surfaced demonstrating delayed ipsilateral intraparenchymal haemorrhage (IPH) as a potential complication of flow diversion treatment of intracranial aneurysms [1], [2], [3]. Common to these reports is that all patients awoke from general anaesthetic at baseline condition, then experienced delayed neurological deterioration (hours to days post-procedure) related to the development of IPH in a vascular distribution ipsilateral, but distal to the treated aneurysm. Although uncommon, the pathophysiology of this process is unknown; hence, we are unable to predict which patients are more susceptible to this potentially severe complication.
In this paper, we report another case of delayed ipsilateral IPH following flow diversion occurring at our institution. Our case is among the most severe examples reported to date, and resulted in death. After describing the case, we critically assess possible mechanisms that have been advanced to explain delayed intraparenchymal haemorrhages in this setting, making use of a novel electrical analogue model based on fundamental fluid dynamics principles.
Section snippets
Case Report
The patient was a 48 year-old woman with a past history of hypertension, hypothyroidism and a known left cavernous internal carotid artery (ICA) fusiform aneurysm of 1.5 cm maximum diameter (Figure 1A). The patient was diagnosed with the initially incidental aneurysm in 2004 following a magnetic resonance imaging (MRI) scan investigating unrelated symptoms of right-sided hearing loss, dizziness, and chronic headaches. At the time of initial diagnosis, the decision was made to follow the aneurysm
Model Analysis
One hypothesis that has been advanced as a possible mechanism of delayed ipsilateral IPH is that replacing the relatively compliant segment of the aneurysm and blood vessel wall with a relatively rigid stent alters pressure transmission across this segment [1], [3]. This has been described as a reduction in the windkessel effect, which refers to a decrease in blood vessel elasticity that leads to an increase in distal pulse pressure [1]. While this hypothesis has not yet been tested in-vivo,
Discussion
Flow diverting stents are relatively new devices in the treatment armamentarium for intracranial aneurysms. These devices are designed to reduce flow into the aneurysmal portion of the artery in order to promote thrombosis within the aneurysm, while maintaining patency of the parent and branch vessels. Flow diverters have also been observed to promote endothelial regrowth across the neck of the aneurysm, further reducing the potential for aneurysm recurrence or recanalisation. The Pipeline
Conclusion
Delayed intraparenchymal haemorrhage after flow diversion is increasingly being recognised as a potentially significant complication and may result in death. Proper counselling of patients prior to treatment should include a discussion of this possible risk. A number of considerations based on established fluid dynamics theory suggest that haemodynamic changes caused by the presence of a flow diverting stent, in place of a compliant aneurysm, are likely to be small and may not provide an
Acknowledgements
Author JPM was supported by a CJ Martin Early Career Fellowship from the National Health and Medical Research Council of Australia.
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Equal first author