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Ongoing intraoperative monitoring techniques for auditory nerve response to stimulation such as clicking sounds include the ABR (auditory brainstem response) test which is most widely used and the cochlear nerve action test. If the waveforms are intact at the end of surgery, it is a sign that hearing is most likely preserved.

There are three primary approaches that surgeons use for resecting (removing) acoustic neuromas. These surgical approaches include:

• Middle fossa approach
• Suboccipital (retrosigmoid) approach
• Translabyrinthine approach

The surgical approach selected is based upon the size of the tumor, the location of the tumor, preoperative level of hearing, importance of hearing preservation, patient preference, and the professional skills of the surgeon. Patients should carefully discuss all the advantages and disadvantages of each approach with their surgeons.

When considering the various surgical approaches, the rates of efficacy and complications as reported in the medical literature are highly variable due to several factors that include:

• Differences in terminology used to describe the same surgical procedures
• Modifications of the surgical approaches that are not described in the studies
• Lack of consistency in reporting the size of the tumor
• Differing criteria for inclusion of patients
• Some studies cite results for "surgery" without defining which approach(es) were included
• Some articles report results for all types of surgery for acoustic neuromas without specifying a particular approach.

Middle Fossa Approach

The middle fossa approach to acoustic neuroma surgery is considered to be very difficult and demanding but offers the surgeon good visualization of the internal auditory canal. A small piece of cranial (skull) bone is removed above the ear canal, providing the surgeon with a good view of small tumors that are situated in the internal auditory canal. The piece of bone is put back at the end of the surgical procedure (craniotomy). The middle fossa approach is typically used if the tumor is small (less than 5 mm. extension into the cerebellopontine angle) and the patient has good preoperative hearing and speech discrimination. During this approach, the surgeon may have to manipulate the facial nerve which may increase the risk of potential complications such as facial nerve injury.

Advantages of the middle fossa approach include:

• Good visualization of the internal auditory canal
• High rates of hearing preservation
• Low rates of facial nerve injury

Difficulties involved with the middle fossa approach include:

• The facial nerve passes through this area increasing the risk of injury which may result in temporary or permanent facial paresis
• Limited exposure of certain structures in the surgical field
• Technically demanding surgery
• May cause injury to the temporal lobe

Suboccipital Approach

The suboccipital approach, also called the retrosigmoid approach can be performed for almost any size tumor. It is more versatile than the cranial middle fossa approach and offers good access to parts of the internal auditory canal and the cerebellopontine angle, a space located behind the internal auditory canal. It is performed most commonly for small tumors when preoperative hearing is good and hearing preservation is a goal of surgery.

The surgeon creates an opening in the cranium behind the mastoid part of the ear (craniotomy) or removes parts of the skull (craniectomy) over the cerebellar portion of the brain. The dura (membrane) is cut which allows drainage of cerebrospinal fluid that allows the cerebellum to move away from the tumor. With this approach, the surgeon is able to view the posterior surface of the tumor in relation to the patient's brainstem and remove the tumor. The dura is then sewn up to prevent further leakage of cerebrospinal fluid. This approach is typically used in the presence of small tumors to reduce the risk of hearing loss. While it offers better chances for hearing preservation, it may decrease the surgeon's ability to view the facial nerve, thus increasing the potential risk of facial nerve complications.