BACKGROUND: The pipeline embolization device (PED) is frequently used in the treatment of anterior circulation aneurysms, especially around the carotid siphon, with generally excellent results. However, treatment of posterior inferior cerebellar artery (PICA) aneurysms with flow diversion (FD) has not been specifically described or discussed. While there are reports of treating PICA aneurysms using placement of FD stents in the vertebral artery, there are no reports of treating these lesions by placement of flow diverting stents in the PICA vessel itself. Due to the unique anatomy and morphology of these aneurysms, it requires special attention. We assessed our multi-institutional experience treating these lesions, including the first reported cases of the PED placed within the PICA. METHODS: Institutional databases of neuroendovascular procedures were reviewed for cases of intracranial aneurysms treated with the PED. Patient and aneurysm data as well as angiographic imaging were reviewed for all cases of PICA aneurysms treated with the PED. PICA aneurysms were defined as aneurysms that involved the PICA. Vertebral aneurysms without disease in the PICA were excluded from the study. RESULTS: 10 PICA aneurysms were treated during the study period. These were classified based on their morphology and location into two main types and five total subtypes for consideration of treatment with flow diversion. All aneurysms were successfully treated, with 8/10 completely obliterated and 2 with a partial reduction in size. Three patients had the PED placed entirely in the PICA and no patient suffered from a medullary or cerebellar stroke. All PEDs were patent and all patients were independent at the last follow-up. CONCLUSIONS: The PED may be used successfully to treat select aneurysms of the PICA. We present the first described cases of successful PED treatment of PICA aneurysms with direct placement of the PED in the PICA vessel itself. The proposed classification system aids in that selection.

OBJECTIVE: The Pipeline embolization device (PED) is frequently used in the treatment of anterior circulation aneurysms, especially around the carotid siphon, with generally excellent results. However, the PED has its own unique technical challenges, including the occurrence of device foreshortening or migration leading to prolapse into the aneurysm. The authors sought to determine the incidence of this phenomenon, the rescue strategies, and outcomes. METHODS: Four institutional databases of neuroendovascular procedures were reviewed for cases of intracranial aneurysms treated with PEDs. Patient and aneurysm data as well as angiographic imaging were reviewed for all cases involving device prolapse into the aneurysm. RESULTS: A total of 413 intracranial aneurysms were treated with PEDs during the study period, by 5 neurointerventionalists. Large and giant aneurysms ( > /= 2 cm) accounted for 32 of these aneurysms. Among these 32 PEDs, prolapse into the aneurysm occurred in 3 patients, with 1 of these PEDs successfully rescued and the other 2 left in situ. No patients suffered any severe complications. The 2 patients in whom the PEDs were left in situ remained on antiplatelet therapy. CONCLUSIONS: The PED may foreshorten or migrate during or after deployment, leading to prolapse into the aneurysm. This phenomenon appears to be associated with large and giant aneurysms, vessel tortuosity, short landing zones, and use of balloon angioplasty. Future study and follow-up is needed to further evaluate this phenomenon, but some of the observations and techniques described in this paper may help to prevent or salvage prolapsed devices.