Background Flow-diverting stents have demonstrated great promise for the treatment of cerebral aneurysms; however, clinical experience with the devices remains very preliminary. We present two cases of spontaneous delayed complications—one fatal aneurysm rupture and one symptomatic increase in aneurysm volume—following the treatment of intradural aneurysms with the Pipeline Embolization Device (PED).

Presentation/intervention Two patients with unruptured, intradural aneurysms of the carotid artery underwent uneventful treatment with the PED (eV3, Irvine, California, USA). One patient, with a giant aneurysm of the carotid terminus, experienced worsening headache 5 days after the procedure and ultimately collapsed and became unresponsive. CT of the head demonstrated acute subarachnoid and intraventricular hemorrhage. The patient died the following day. A second patient with a large left posterior communicating artery aneurysm presented with progressive memory loss 3 months after PED reconstruction of the carotid artery. Although serial CT angiograms showed progressive thrombosis of the aneurysm to near-complete occlusion, MR of the brain demonstrated marked interval growth of the collective aneurysm–intra-aneurysmal thrombus mass with extensive edema throughout the adjacent left temporal lobe.

Conclusions Flow-diverting devices have demonstrated tremendous promise for the treatment of complex, unruptured cerebral aneurysms. However, experience with this novel approach to aneurysm treatment is preliminary and the consequences of its application within the cerebrovasculature remain incompletely defined. Mural destabilization resulting in delayed, spontaneous, aneurysm growth and/or rupture may occur in the days to weeks following the application of flow-diverting devices to treat previously unruptured intracranial aneurysms. A better understanding of the incidence and etiology of these complications is essential for this technology to be optimally applied.