Quantitative Assessment of In-Stent Stenosis After Pipeline Embolization Device Treatment of Intracranial Aneurysms: A Single-Institution Series and Systematic Review

BACKGROUND: Very little is known about the incidence of in-stent stenosis after flow diverter treatment of intracranial aneurysms. We sought to evaluate the incidence and clinical significance of in-stent stenosis at angiographic follow-up after Pipeline embolization device (PED) placement using quantitative measures. METHODS: The clinical and radiological records from all patients undergoing PED treatment of intracranial aneurysms at a major U.S. academic center from March 2013 to July 2017 were retrospectively reviewed. A modified version of the North American Symptomatic Carotid Endarterectomy criteria was used to quantify the degree of stenosis on the most recent postprocedural angiogram. The percentage of stenosis was calculated as 1 - (narrowest vessel diameter/ maximal midstent diameter within the artery) at the first follow-up angiogram. The PubMed, Web of Science, and EMBASE databases were additionally searched from inception until April 2018 for the rates of in-stent stenosis after flow diversion. RESULTS: A total of 155 patients (mean age, 58.3 years; 30 males) with 162 aneurysms underwent treatment with the PED at our institution. In-stent stenosis was detected in 12 patients (7.1%) at 6 months. The mean percentage of stenosis was 39.7%. All 12 patients remained asymptomatic, except for 1 who developed hemiplegia secondary to an unrelated ischemic stroke. The aneurysm occlusion rates at 6 months were comparable between the stenosis and nonstenosis cohorts (76.9% and 71.6%, respectively). Within the stenosis cohort, further follow-up angiograms after 6 months were available for 6 patients, of whom 3 (50%) had either complete resolution or improvement. Of the 43 included studies, 28 reported on the use of the PED, with 2448 patients. The mean reported rate of in-stent stenosis after PED placement was 8.8% (range, 0%-39%). CONCLUSIONS: In-stent stenosis remains a rare complication of PED placement for intracranial aneurysms. When occurring, it appears to largely be self-limiting, with a benign clinical course.