The Source for Neurovascular News and Education

July 14, 2024


Key Points:

  • Assessment of DWI and FLAIR lesions following flow diversion using Pipeline
  • De novo FLAIR lesions distinct from DWI lesions have unclear etiology, implications


Flow diverter therapy for the treatment of intracranial aneurysm using pipeline flow diversion is associated with an increased rate of delayed fluid-attenuated inversion recovery (FLAIR) lesions on magnetic resonance imaging (MRI), according to a study published online January 28, 2016, ahead of print in Stroke. These lesions appear to be distinct from perioperative diffusion weighted imaging (DWI) lesions, so both their cause and clinical implications remain unclear.

In a recent report, the authors, led by Adel M. Malek, MD, PhD, of Tufts Medical Center (Boston, MA), found that deployment of the Pipeline Embolization Device (Covidien) led to a higher rate of ipsilateral periprocedural DWI lesions than conventional stent-coil methods. “This high periprocedural rate has been replicated by an outside group with an almost identical rate of 50.9% when compared with 52% of patients in our initial study. In this light, we have elected to follow [Pipeline device] patients closely and assess them for delayed ischemic events,” they write.

To further evaluate ischemic risk of Pipeline patients, Dr. Malek and colleagues assessed 41 consecutive patients undergoing aneurysm treatment with the Pipeline device as well as a comparison group of 78 patients undergoing Neuroform stent-mediated embolizations. They used serial MRIs to identify the presence of newly occurring DWI and FLAIR lesions at multiple postprocedure time ranges. Pipeline patients had postprocedure assessments, on average, on days 1 (T1), 73 (T2), 174 (T3), 277 (T4), and 409 (T5). Neuroform patients had postprocedure assessments, on average, on days 1 (T1), 107 (T2), and 335 (T4). The investigators also estimated the DWI or FLAIR burden by lesional diameter summation.

Pipeline patients were more likely to have new ipsilateral FLAIR lesions and a greater mean FLAIR burden than Neuroform patients at all time points studied (table 1).


Overall, 34% of Pipeline patients experienced a new FLAIR lesion at any of the study time points, compared with only 10% of the Neuroform patients. Postprocedural DWI did not predict future FLAIR lesions, suggesting the cause of these lesions was not related to the procedure.

Implications of De Novo Lesions Remain Unclear

“Flow-diversion … relies on redirecting blood flow, and thereby causing stasis within the aneurysm,” the authors explain. “This stasis causes thrombosis and an inflammatory response with eventual sealing of the aneurysm neck by endothelialization and neointimal growth with the stent as a scaffold.”

Flow remains in and out of the aneurysm until it is “completely occluded by thrombus and aneurysmal neck neointimal formation along the stent,” Dr. Malek and colleagues write, adding that the “rate of thrombus egress or escape” during the transition from implantation to healing remains unclear.

Just what is causing the lesions and what their clinical effect may be is unknown, the authors conclude, suggesting the need “prudent follow-up and evaluation.” 

Safain MG, Roguski M, Heller RS, et al. Flow diverter therapy with the pipeline embolization device is associated with an elevated rate of delayed fluid-attenuated inversion recovery lesions. Stroke. 2016;Epub ahead of print.



  • Dr. Malek reports receiving funding from ev3-Covidien, Siemens, and Stryker Neurovascular .