Although histologically benign (no malignant growth) vestibular schwannomas grow in a critical location, adjacent to vital brain structures, nerves and blood vessels. One of the most critical of these is called the facial nerve (or the seventh cranial nerve) which controls movement of the facial muscles. The facial nerve often closely adheres to the capsule of the tumour resulting in it being extremely stretched and thinned out. This makes surgery on vestibular schwannomas very delicate as the facial nerve is very susceptible to damage during surgery. Thus, it is critical to use special surgical techniques to preserve the function of the facial nerve.
Facial nerve preservation is enabled through the use of intra-operative facial nerve monitoring. This is a technique which utilises tiny electrodes placed into the facial muscles at the commencement of the procedure. Using special anesthetic techniques and a nerve stimulator the position and course of the entire facial nerve is accurately plotted. This allows doctors to ensure preservation of the facial nerve during the excision of the tumour.
In addition to the facial nerve, other critical nerves like the trigeminal nerve (or fifth nerve) which control sensation over the head and face is also closely located to the tumour. The lower cranial nerves which are responsible for voice and swallowing are located below the tumour and are also critically important nerves which need to be carefully preserved. This tumour often extends into the skull bone (internal auditory canal). This portion of the tumour must be addressed by drilling part of the skull bone internally and removal of ‘the tail’ of the tumour to prevent any future regrowth. In patietns with longstanding or very large tumours, complete excision may carry the risk of nerve injury and hence some microscopic remnants of tumour might need to be left behind which can be addressed with gamma knife radio surgery post operatively.