Perianeurysmal Edema After Embolization with Flow Diversion

Flow diversion is an endovascular technique for embolization of intracranial aneurysms using a semi-porous stent to that redirects blood flow away from the aneurysm and is a scaffold for vessel remodeling. With flow diversion, aneurysms close slowly over 6-12 months as endothelial growth into the stent covers the neck of the aneurysm. Flow diversion is the preferred treatment for unruptured, large, paraclinoid aneurysms, which are otherwise challenging to treat with conventional open surgical or endovascular techniques. Post-embolization perianeurysmal edema (PAE) is an uncommon complication that occurs weeks to months after embolization and manifests as brain parenchymal edema surrounding the treated aneurysm. The clinical presentation is varied and includes headache, seizure or focal neurologic deficit. Frequently, PAE is misdiagnosed as an embolic stroke, which is a more common post-embolization complication and has some clinical and imaging overlap. PAE can be differentiated from ischemia by the absence of restricted diffusion and aneurysm wall enhancement on post-contrast Magnetic Resonance Imaging (MRI). PAE was initially described following coil embolization, but has subsequently been observed after flow diversion alone or with adjunctive coiling. Post-embolization PAE presumably results from rapid aneurysm thrombosis, endothelial cell necrosis, and the ensuing inflammatory reaction, which spreads to the adjacent brain parenchyma. Early recognition of PAE is critical to initiate appropriate therapy.