Audiologic prognostic factors for hearing preservation following vestibular schwannoma surgery

Background: Postoperative hearing loss after vestibular schwannoma (VS) removal still remains a lifelong problem for the patients. The present study analyzes the problem of hearing preservation after VS removal from a different angle than available professional literature on this topic.

Objectives: To identify audiologic factors which determine the extent of hearing loss in patients operated on for VS.

Material and methods: The study group included 86 patients operated on due to VS accessed via the middle cranial fossa. The analyses involved the effect on absolute hearing loss, which was calculated on the basis of the results of pure-tone audiometry performed preand postoperatively, and factors included in the preoperative audiologic tests, such as pure-tone audiometry, speech audiometry, auditory brainstem response (ABR), and impedance audiometry.

Results: The following parameters were demonstrated to have a prognostic value: 1. hearing thresholds at 125 Hz, 500 Hz and 1,000 Hz for the operated ear, Pure Tone Average (PTA) - calculated specifically at 500 Hz, 1,000 Hz and 2,000 Hz and at 500 Hz, 1,000 Hz, 2,000 Hz, and 4,000 Hz for the operated ear, and normal audiometric curve; 2. speech discrimination ranging from 55 dB to 75 dB for the operated ear, speech detection threshold (SDT) in the operated ear and interaural difference at 25-35 dB (non-operated vs operated ear); 3. presence of wave V, the values of I-V and III-V intervals for the operated ear, the amplitude of wave V, and the interaural ratio of wave V amplitudes; 4. intensity level for obtaining stapedial reflex or an abnormal reflex at Ipsi 500 Hz, 1,000 Hz and 2,000 Hz, and Contra 500 Hz, 1,000 Hz, 2,000 Hz, and 4,000 Hz.

Conclusions: The better the preoperative hearing status, the more substantial surgery-related hearing loss was observed. A number of preoperative parameters of the basic diagnostic set of audiologic tests present a prognostic value for the degree of surgery-related hearing loss in VS patients.