question: OBJECT Delayed ipsilateral intraparenchymal hemorrhage has been observed following aneurysm treatment with the Pipeline Embolization Device (PED). The relationship of this phenomenon to the device and/or procedure remains unclear. The authors present the results of histopathological analyses of the brain sections from 3 patients in whom fatal ipsilateral intracerebral hemorrhages developed several days after uneventful PED treatment of supraclinoid aneurysms. METHODS Microscopic analyses revealed foreign material occluding small vessels within the hemorrhagic area in all patients. Further analyses of the embolic materials using Fourier transform infrared (FTIR) spectroscopy was conducted on specimens from 2 of the 3 patients. Although microscopically identical, the quantity of material recovered from the third patient was insufficient for FTIR spectroscopy. RESULTS FTIR spectroscopy showed that the foreign material was polyvinylpyrrolidone (PVP), a substance that is commonly used in the coatings of interventional devices. CONCLUSIONS These findings are suggestive of a potential association between intraprocedural foreign body emboli and post-PED treatment-delayed ipsilateral intraparenchymal hemorrhage.