Is delayed haemorrhage a complication following treatment with a flow diverter?


A recently published study reports that delayed ipsilateral parenchymal haemorrhage may occur after the treatment of anterior circulation aneurysms with flow diverters. The study was published in the American Journal of Neuroradiology.

The authors, Thomas R Marotta, St Michael’s Hospital, Toronto, Canada, and colleagues Juan Cruz, David Fiorella, and Cian O’Kelly wrote that this complication does not seem to be restricted to a specific aneurysm subtype and does not seem to be related to an intraprocedural complication or solely attributable to dual antiplatelet treatment.

Marotta et al reported four cases of delayed ipsilateral parenchymal haemorrhage following the technically successful treatment of anterior circulation aneurysms with the Pipeline Embolization Device.

The Pipeline Embolization Device is a flow-diverting stent designed for the treatment of cerebral aneurysms.

The investigators analysed both clinical and imaging data from all patients undergoing aneurysm treatment with the Pipeline Embolization Device at two institutions to assess the incidence of delayed ipsilateral parenchymal haemorrhage after treatment with the device.


Authors of the paper noted that a total of 66 patients (47 anterior circulation) with cerebral aneurysms underwent treatment with a Pipeline Embolization Device between January 2008 and November 2010. “Four patients experienced delayed periprocedural ipsilateral parenchymal haemorrhage, all after the treatment of anterior circulation aneurysms (8.5%, 4/47). The aneurysm size ranged from 5 to 21mm. All ipsilateral parenchymal haemorrhages occurred within the cerebral hemisphere, ipsilateral to the treated aneurysm, and were anatomically remote from the treated aneurysms,” the authors wrote.

They further clarified that all procedures had been uncomplicated, and that the patients had emerged from general anaesthesia at neurologic baseline. “The haemorrhages became clinically evident between one and six days after the procedure. Two patients had unfavourable outcomes (mRS scores, 4 and 6),” they wrote.

Marotta spoke to NeuroNews about the study.

What is the importance of this study?

This study provides additional evidence to support the concept that delayed ipsilateral parenchymal haemorrhage may occur after treatment with flow diverters. Unlike delayed growth or rupture of cerebral aneurysms after flow diversion which can be clearly attributed to the aneurysm/treatment, parenchymal haemorrhage presents more of a conundrum. Since the haemorrhages are remote to the aneurysm and the bleeds typically occur days to weeks after the treatment, it is difficult to understand how the event could be related to the aneurysm or the treatment. The findings that the bleeds are all ipsilateral to the treated aneurysm and occur at a frequency which far exceed what would be expected within the context of a few weeks of treatment with dual antiplatelet medications support the idea that these events are somehow treatment or device related. Changes related to the windkessel effect may act as a triggering event for the parenchymal haemorrhage in a more susceptible distal circulation. This hypothesis may be one step toward a more complete understanding of the phenomenon and how to avoid it. 

What is your message to interventionalists based on the results of this study?

Flow diversion represents a quantum advance for the treatment of some of the most difficult and lethal aneurysms we encounter. At the same time, we are still working to understand its optimal application and limitations. The complications we encounter with flow diversion differ from those commonly seen with the endovascular treatment of aneurysms. Delayed ipsilateral parenchymal haemorrhage after PED reconstruction of aneurysms is a low frequency event, but one that must be recognised as potentially related to the treatment. Unlike aneurysm rupture, delayed ipsilateral parenchymal haemorrhage does not appear to be related to the size or intradural location of the aneurysm. As such, this potential complication (observed in 8.5% of our patients with anterior circulation aneurysms) should be integrated into the risk assessment when one considers treating a smaller unruptured aneurysm which may be amenable to better understood and potentially safer conventional treatments. 

What are the limitations of the study?

This is a small retrospective study, susceptible to the usual biases inherent to this design. Based on lower incidence in other studies (PITA, PUFS), our number (8.5%) may represent an overestimation of the actual risk for the treatment of anterior circulation aneurysms. As a result of our small sample size, the 95% confidence interval (2.8%–21.3%) is relatively wide.