Microhemorrhagic transformation of ischemic lesions on T2*-weighted magnetic resonance imaging after Pipeline embolization device treatment.

OBJECTIVE The authors sought to demonstrate that hemorrhagic transformation of ischemic lesions is the main cause of delayed intracerebral hemorrhage (ICH) after Pipeline embolization device (PED) treatment and to estimate the rate of hemorrhagic transformation of new postprocedure ischemic lesions. METHODS Patients who underwent PED placement (PED group) from November 2015 to March 2017 or stent-mediated embolization (EN group) from December 2010 to October 2015 were retrospectively analyzed. Pre- and postprocedural MR images and 6-month follow-up MR images for each patient were scored for the presence of postprocedural bland ischemic and hemorrhagic lesions using diffusion-weighted MRI (DWI) and T2*-weighted MRI (T2*WI), respectively. RESULTS The PED group comprised 28 patients with 30 intracranial aneurysms, and the EN group comprised 24 patients with 27 intracranial aneurysms. The mean number of ischemic lesions on DWI 1 day postprocedure was higher in the PED group than in the EN group (5.2 vs 2.7, p = 0.0010). The mean number of microbleeds detected on T2*WI 6 months postprocedure was higher in the PED group than in the EN group (0.6 vs 0.15, p = 0.028). A total of 36.7% of PED-treated patients exhibited new microbleeds on T2*WI at 6 months postprocedure, with at least 77.8% of these lesions representing hemorrhagic transformations of the new ischemic lesions observed on day 1 postprocedure. The rate of adjunctive coil embolization (27.3% vs 0.0%, p = 0.016) and the mean number of ischemic lesions observed 1 day postprocedure (6.6 vs 4.3, p = 0.020) were predictors of subsequent microbleeds in the PED group. CONCLUSIONS New microbleeds detected using T2*WI at 6 months postprocedure were more common after PED treatment than after stent-mediated embolization. Approximately three-quarters of these lesions were hemorrhagic transformations of new ischemic lesions observed on day 1 postprocedure. Prevention of intraprocedural or postprocedural infarcts is necessary to reduce the risk of hemorrhagic complications following PED placement.