Cerebral foreign body reaction (CFBR) after endovascular treatments is a rare event to be aware of: case series and review of literature.

Cerebral foreign body reaction (CFBR) due to hydrophilic polymer embolization is a rarely diagnosed complication of cerebral endovascular procedures. Despite the considerable use of endovascular treatment in the literature, few cases of CFBR have been described so far. Our main objective is to describe three patients who were diagnosed at our center with CFBR and provide an overview of the existing literature. In these three cases, cerebral aneurysms were treated with different endovascular techniques as Contour device implantation, coil embolization, and flow diversion stent. Only one patient manifested focal neurological signs characterized by contralateral strength deficit, dysarthria, and headache. In the other two cases, the lesions were asymptomatic and were found at follow-up imaging. Brain MRI showed hyperintense lesions in FLAIR sequences in subcortical white matter without diffusivity restriction on diffusion-weighted imaging (DWI) corresponding to contrast-enhancing foci in T1-weighted images, suggestive of CFBR. Pathophysiology and predisposing factors are still unclear. Corticosteroid therapy led to marked improvement at neuroimaging in all cases and to a clinical remission in the first case. Our data confirm that CFBR is an underestimated complication to be aware of, in both neurological and neuroradiological practice.