Recurrent Foreign Body Reactions to Neuroendovascular Polymers—A Clinicopathologic Case Study

Objective We provide histopathologic and neuroimaging evidence of recurrent foreign body reactions in a patient following separate stent-assisted coiling of two contralateral intracranial aneurysms a decade apart. Background Stent-assisted endovascular coiling for wide-neck cerebral aneurysms introduces permanent foreign materials into the cerebral vasculature. While foreign body reactions after endovascular coiling are increasingly reported in the literature, compelling histopathologic data remains very limited. Design/Methods Electronic medical record review for clinical details and neuroimaging. Histopathology was extensively reviewed with a neuropathologist. Results A 37-year-old woman presents with left arm weakness. Magnetic resonance imaging (MRI) shows numerous enhancing lesions with large multifocal T2 FLAIR changes in the right hemisphere. An extensive vascular, infectious, autoimmune, and neoplastic workup returns negative. Months earlier, she had undergone stent-assisted coiling of a right internal carotid artery (ICA) aneurysm. A decade prior, she had presented with focal right-sided seizures after coiling of a left ICA aneurysm; MRI brain at the time revealed two enhancing lesions in the left hemisphere of unclear etiology. A brain biopsy is performed, and histopathology reveals multifocal, chronic micro-abscesses characterized by collections of neutrophils surrounded by a rim of multinucleated giant cells and histiocytes which are in turn rimmed by fibrosis and granulation tissue. Staining is negative for neoplastic changes and infectious organisms. Rare filamentous structures are identified in association with the giant cells; these resemble coil polymers described in the endovascular literature and are highly suspicious for inducing a neuroinflammatory foreign body reaction. She improves following glucocorticoid treatment, and repeat imaging shows substantial reduction in parenchymal abnormalities. Conclusions Foreign body reactions are an uncommon complication of endovascular aneurysm coiling and can manifest as an embolic inflammatory phenomenon. These neuroinflammatory reactions are driven by endovascular polymers and responsive to glucocorticoid treatment. Heightened awareness can facilitate earlier diagnosis and treatment, with prompt neuroimmunology consultation for repeat endovascular procedures.