Hearing Preservation in Vestibular Schwannoma
Postoperative improvements in hearing in patients with vestibular schwannoma are extremely rare.
Despite no universally accepted definition of hearing preservation following vestibular schwannoma treatment, numerous variables have been identified as possible factors that may affect hearing outcomes following radiotherapy. Age, pretreatment hearing, radiation dose, tumor location and tumor size, length of follow-up, fractionation, and timing of radiation have all been explored, among other variables, as factors related to hearing outcomes following radiation 1).
Prophylactic nimodipine treatment and improvement in hearing outcome after vestibular schwannoma surgery
In clinical routines, neuroprotective strategies in neurosurgical interventions are still missing. A pilot study (n = 30) and an analogously performed Phase III trial (n = 112) pointed to a beneficial effect of prophylactic nimodipine and hydroxyethyl starch (HES) in vestibular schwannoma (VS) surgery. Considering the small sample size, the data from both studies were pooled. METHODS The patients in both investigator-initiated studies were assigned to 2 groups. The treatment group (n = 70) received parenteral nimodipine (1-2 mg/hour) and HES (hematocrit 30%-35%) from the day before surgery until the 7th postoperative day. The control group (n = 72) was not treated prophylactically. Facial and cochlear nerve functions were documented preoperatively, during the inpatient care, and 1 year after surgery. RESULTS Pooled raw data were analyzed retrospectively. Intent-to-treat analysis revealed a significantly lower risk for hearing loss (Class D) 12 months after surgery in the treatment group compared with the control group (OR 0.46, 95% CI 0.22-0.97; p = 0.04). After exclusion of patients with preoperative Class D hearing, this effect was more pronounced (OR 0.38, 95% CI 0.17-0.83; p = 0.016). Logistic regression analysis adjusted for tumor size showed a 4 times lower risk for hearing loss in the treatment group compared with the control group (OR 0.25, 95% CI 0.09-0.63; p = 0.003). Facial nerve function was not significantly improved with treatment. Apart from dose-dependent hypotension (p < 0.001), the study medication was well tolerated. CONCLUSIONS Prophylactic nimodipine is safe and may be recommended in VS surgery to preserve hearing. Prophylactic neuroprotective treatment in surgeries in which nerves are at risk seems to be a novel and promising concept. Clinical trial registration no.: DRKS 00000328 ( https://drks-neu.uniklinik-freiburg.de/drks_web/) 2).
SRS resulted in a high rate of long-term tumor control and cranial nerve preservation. The Pittsburgh Hearing Prediction Score (PHPS) helped to predict long-term hearing preservation rates in patients who underwent SRS when they still had a serviceable hearing. The best long-term hearing preservation rates were found in younger patients with smaller tumor volumes 3).
Hearing preservation in VS surgery may be accomplished via the middle fossa or retrosigmoid approaches. Appropriate patient selection and surgical approach is critical in achieving the best hearing outcomes. This article highlights the preoperative assessment, patient selection and prognostic factors, intraoperative monitoring of hearing, and surgical approaches to optimize hearing preservation during VS removal 4).
In a systematic review of the literature on the spontaneous course of hearing in patients observed with a vestibular schwannoma. Included studies were appraised using the Grading of Recommendations Assessment, Development and Evaluation system.
PubMed, Embase, Medline, Cochrane library, and CINAHL (Cumulative Index to Nursing and Allied Health Literature) were searched for literature on hearing in patients observed with a vestibular schwannoma.
Of 217 evaluated papers, 15 were included, representing a total of 2,142 patients. Main Outcome Measures Hearing according to the AAO-HNS (American Academy of Otorhinolaryngology- Head and Neck Surgery) classification system. Weighted average of the proportion of patients preserving good hearing (>70% discrimination score and pure tone audiometry [PTA] < 30dB) and serviceable hearing (>50% discrimination score and PTA < 50dB) was determined. Results Fifty percent of patients presenting with good hearing at diagnosis had preserved this after a mean of 5 years of observation, whereas serviceable hearing was preserved in 54%. Patients with normal discrimination at diagnosis preserve their hearing very well. Very few studies exist on long-term hearing preservation.
After 5 years of observation, around half of patients will have preserved good or serviceable hearing. Patients with normal discrimination at diagnosis are more likely to preserve good hearing 5).
The focus of vestibular schwannoma surgery has shifted from low mortality and tumor resection to retention of neurological function. Hearing preservation is another point in addition to facial nerve function preservation. Hearing preservation rates overall ranged from 2% to 93% in recent studies. Characteristics such as approach, pre-operative neurological function, tumor size, nerve of origin and fundal fluid of the internal auditory canal have been reported as possible influencing factors 6).
Translabyrinthine approach is a useful approach for resection of vestibular schwannomas in cases where hearing preservation is not a concern. Additionally Morrison and King have described a modified use of this approach in combination with a transtentorial approach for the resection of vestibular schwannomas and other cerebellopontine angle tumors and proximate anatomy 7).
Refinement of intraoperative auditory monitoring may improve postoperative hearing. We have introduced a newly designed intracranial electrode enabling continuous monitoring of the cochlear nerve compound action potential (CNAP). We performed simultaneous monitoring of the auditory brainstem response (ABR) and CNAP during retrosigmoid small AN removal, and clarified the surgical outcome and the usefulness of CNAP monitoring.
Hearing preservation can be expected after removal of the acoustic neurinomas under the following situations; hearing acuity of less than 50-60dB in preoperative pure tone audiogram, tumor size of less than 20 mm in maximum diameter, cases with preservation of cochlear nerve and of the internal auditory artery during the operation, and no injury to the labyrinth during the operation. In some cases, tinnitus becomes aggravated in the case with cochlear nerve preservation associated with unserviceable hearing. Furthermore, the degree of tinnitus shows a decrease as postoperative hearing improves in some cases 8).