Synthetic material. Foreign bodies from duraplasty, microvascular decompression surgery, vessel wrapping or grafting, and artifacts from materials unintentionally implanted into tissue may also be seen. Examples of these include silicone fibers, shredded Teflon felt used in microvascular decompression, and PVA sponges (also microvascular decompression). (A, B) Biomesh dural replacement. Silicone fibers are seen as transparent, uniform, round fibrils with minimal pigmentation (A). CD68 immunohistochemistry shows the silicone fibers within the cytoplasm of multinucleate giant cells (B). (C, D) Teflon. Transparent fibers of shredded Teflon fleece in fibrous tissue (C) and in the cytoplasm of multinucleate giant cells (D). (E, F) PVA sponge. The porous, basophilic material embedded in agar is characteristically vacuolated with slightly irregular borders (E). CD68 immunohistochemical stain again displays multinucleate giant cells surrounding the PVA fragments (F). Scale bar = 100 µm.