Foreign body-type giant cell reaction post intracranial endovascular clot retrieval: a postmortem case.

Background and aims: Endovascular clot retrieval (ECR) has revolutionised acute ischaemic stroke management. While procedural safety is well established, little attention has been paid to vascular responses to hydrophilic polymer coatings used on retrieval devices. This report presents postmortem histopathological findings implicating a foreign body giant cell reaction secondary to hydrophilic polymer exposure as a cause of recurrent stroke following ECR. Methods: A detailed clinical and neuropathological review was conducted on a 72-year-old patient who experienced three sequential ischaemic strokes within 4 months following ECR and angioplasty of a right middle cerebral artery (M2) occlusion. Limited postmortem examination of the heart and brain was undertaken with histopathological and immunoperoxidase staining to assess potential vascular inflammatory mechanisms. Results: Postmortem examination demonstrated multiple infarcts of differing ages, diffuse atherosclerotic change and a florid multinucleated giant cell reaction containing non-polarisable basophilic material along the luminal surface of the right M2 segment and adjacent vessels. The internal elastic lamina remained intact, with only focal fibrinoid necrosis and sparse medial inflammation. No amyloid angiopathy, vasculitis or cardiac embolic source was identified. The morphological features were consistent with a chronic inflammatory response to embolised hydrophilic polymer coating material from prior endovascular instrumentation. Conclusions: This case highlights an under-recognised mechanism of post-ECR recurrent stroke linked to hydrophilic polymer-induced vascular inflammation. If recognised antemortem, immunosuppression may be more effective than usual secondary stroke prevention treatments.