Many ablative procedures are effective for hemifacial spasm (HFS) (including sectioning of divisions of the facial nerve), however, this leaves the patient with some degree of facial paresis. The current procedure of choice for HFS is microvascular decompression (MVD) wherein the offending vessel is physically moved off of the nerve, and a sponge (e.g. Ivalon®, polyvinyl formyl alcohol foam) is interposed as a cushion. Other cushions may not prove to be as satisfactory (muscle may disappear, and Teflon felt may thin 1).
Compression of the trigeminal root entry zone, caused by the prosthesis itself or by severe adhesions, has been reported by several authors 3) 4) , and even indirect vascular compression caused by fairly hard implants like Ivalon has been reported 5) 6).