Surgical Treatment for Acoustic Neuromas
Surgery vs. Radiosurgery
Intervention options for acoustic neuromas include observation, surgery and radiosurgery. Determining optimal treatment varies based on several factors, including: tumor size, whether the tumor has caused neurologic damage prior to treatment and patient preferences.
Because acoustic neuromas are usually slow-growing, immediate intervention is not always necessary. For patients with very small, asymptomatic tumors, some elderly patients, or patients with medical complications, a conservative approach with observation including serial MRI studies may be reasonable.
Considering the Options
The options for the treatment of the acoustic neuromas include surgery and radiosurgery. Radiosurgery is a relatively non-invasive treatment that uses narrow beams of radiation to both treat the acoustic neuroma while minimizing the dose of radiation delivered to the surrounding tissues.
Considerations in Choice of Treatment
Controversy exists regarding the optimal form of treatment for the acoustic neuromas. Small tumors do not typically pose a risk to brain function and may not present with noticeable symptoms. These smaller tumors may be monitored over time with imaging studies, including MRI scans. For larger tumors, intervention options may be indicated. For both surgery and radiotherapy approaches to acoustic neuroma treatment, the important issues to consider are preservation of the facial nerve, preservation of hearing and control of the tumor. "Control of the tumor" is a phrase that should be considered carefully.
Microsurgical resection (removal) of acoustic neuromas can be accomplished using one of three operative approaches.
- A sub-occipital approach offers preservation of hearing sensitivity and preservation of the seventh (facial) nerve function. The success rates with hearing preservation are inversely related to tumor size (removal of large acoustic neuromas may result in more significant declines in hearing sensitivity). Hearing preservation after surgery for acoustic neuroma removal varies between reported groups of patients. Approximately half of patients with small tumors who have useful hearing prior to surgery will preserve hearing post-operatively.
- A translabyrinthine approach for removal of the acoustic neuroma may be chosen when significant hearing loss is present and to improve visualization of the seventh nerve and internal auditory canal. This surgical approach results in complete loss of ipsilateral hearing in virtually all patients.
- The middle fossa approach may be considered for smaller, intra-canalicular acoustic neuromas in patients where hearing preservation is important. A higher incidence of seventh nerve palsy has been reported with the middle fossa approach in comparison with the sub-occipital approach, particularly if the tumor lies in a low, dependent position within the internal auditory canal.
Surgical removal of acoustic neuromas have been aided by the following technological advances, including:
- Intraoperative monitoring of brain and nerve function is now routinely performed with all surgical procedures for the resection of acoustic neuromas.
- Image-guided surgery brings together the skills of experienced surgeons with two- and three-dimensional images of the skull base obtained using CT or MRI scans. Graphic displays in the operating room link those images to the sterile instruments used by the surgeons, so that the instrument tips in real space also appear in the virtual space of the CT or MRI images. The virtual surgical field allows the surgeon to predict what lies ahead, to avoid damaging vital structures and to assure complete tumor removal.
