The Method for Placement of an Intraoperative Continuous Facial Nerve Stimulating Electrode in Acoustic Neuroma Surgery: Technical Note.

Preservation of facial nerve (FN) function is the most important goal in acoustic neuroma (AN) surgery. We have been using intraoperative continuous facial nerve monitoring (ICFNm) of evoked electromyography during AN surgery. ICFNm is very useful, and we can identify the real-time functions of the FN. Some surgeons have experienced difficulty with placing the ICFN stimulating electrode (SE). We therefore show how to place the ICFN SE. We mostly perform AN surgery with a retrosigmoid approach (RSA). A craniotomy with four burr holes is performed. We dissect the arachnoid membrane along the accessory nerve from the cisterna magna to the glossopharyngeal nerve. When we are able to identify the root exit zone (REZ) of the FN near the brainstem, we place the ICFN SE on it. However, when a large tumor covers the REZ, we have to debulk the tumor to create a space between the tumor and the glossopharyngeal nerve. After that, we can place the SE on the REZ. A method for placement of the ICFN SE is needed for some techniques of AN surgery. Once we learn how to place the SE, we can identify continuous FN function during AN surgery. This method is useful for the preservation of postoperative FN function in AN surgery.