Changing Criteria for Attempts at Hearing Preservation in Acoustic Neuroma Surgery

Background In the evolution of microsurgical treatment for acoustic neuromas, more complex and larger tumors have been operated on with an attempt to preserve hearing. Technological innovations and refinement of techniques have made preservation of hearing more possible. Two monitoring techniques have been particularly helpful: auditory brain response and direct monitoring of cranial nerve VIII. Notably, direct cranial nerve VIII monitoring has allowed us to ascertain various mechanisms of nerve distress with faster processing time intraoperatively. With these advancements, more patients have become candidates for hearing preservation surgery when compared with previous studies.

Methods We retrospectively reviewed 87 patients who were treated between 2010 and 2016 to preserve hearing. Thirty (34%) of these patients were men. The average age was 51 years (range: 16–72). Presenting symptoms were similar to those described in other series of acoustic neuromas with the most frequent being hearing loss. Tumor measurements were made using preoperative MRIs and size was defined as maximum tumor diameter. Tumor sizes ranged from 0.8 to 5.6 cm with an average diameter of 2.24 cm. Patients were selected for hearing preservation surgery based on preoperative hearing function, tumor size, and location. Retrosigmoid (74 patients), modified translabyrinthine (10 patients), and middle fossa (3 patients) approaches were used.

Audiometry was performed both pre- and postoperatively by the Audiology Department. Audiometry consisted of pure tone threshold average (PTA) and speech discrimination (SD). This was then stratified into levels of hearing function according to the American Academic of Otolaryngology–Head and Neck Surgery (AAO-HNS) with classes ranging from A to D corresponding to normal (A) and non-serviceable (D) hearing. Of the 87 patients in this study, 63 (72%) had complete pre- and postoperative audiometric data available.

To analyze how hearing preservation in acoustic neuroma has evolved, we compared the results of this study with a study by the senior authors (J.P.L. and D.E.A.) had previously published.

Results In our previously published series, 9.26 tumors were treated surgically to preserve hearing per year. In this series, this metric increased to 14.5 tumors per year. Of the patients with complete sets of audiometric data, 51 patients (81%) had measurable hearing as indicated by either a PTA < 120 dB or an SDS > 0% which improved from 66.2% previously. Additionally, 42 patients (66%) had a SDS score > 50% compared with 45.3% reported previously.

Conclusion Technological advancements and refinement of technique have changed the criteria for attempting hearing preservation for patients undergoing microsurgical resection of acoustic neuromas. Specifically, direct cranial nerve VIII monitoring has allowed us to better delineate the mechanisms of pathophysiology leading to hearing loss intraoperatively, thereby prompting strategic alterations of technique in real time. As microsurgical treatment of acoustic neuromas continues to evolve, the standard of care continues to increase. With the use of these new techniques, increasing the number of patients with hearing preservation surgery may be possible.

No conflict of interest has been declared by the author(s).