Hearing improvement after middle fossa resection of vestibular schwannoma

Objective: The preoperative, intraoperative, and postoperative variables of patients experiencing hearing improvement after middle fossa resection of vestibular schwannomas were evaluated as potential prognostic indicators. Study Design: Retrospective case review with new objective postoperative da ta collected on patients with documented hearing improvement. Setting: California Ear Institute at Stanford and Stanford University Hospi tal, a tertiary referral center. Patients: The patient group consisted of 30 consecutive patients undergoing middle fossa approach to vestibular schwannoma between October 24, 1994, a nd November 11, 1998. Intervention: Hearing preservation surgery via the mi ddle cranial fossa approach was performed on all patients. Main Outcome Measures: Pure-tone averages (PTAs) and speech discrimination scores (SDS) were used to document hearing preoperatively and postoperative ly. Preoperative electrophysiologic studies of auditory brainstem response, electronystagmography, electrical neuronography, transient evoked otoacous tic emissions, and distortion product otoacoustic emissions were evaluated. Intraoperative continuous nerve action potential and auditory brainstem re sponse tracings were reviewed. Postoperative auditory brainstem response an d transient evoked otoacoustic emissions were obtained when possible on pat ients whose hearing improved. Statistical analysis was completed using Stud ent's t test and chi-square test. Results: Seventeen (57%) of 30 patients with tumors ranging from 2 to 31 mm maintained hearing postoperatively, Among patients with hearing preservati on, 7 (41% or 23% of the overall group) exhibited hearing improvement (PTA( 2) improved by greater than or equal to5 dB and/or SDS improved by greater than or equal to 12%). Three of these 7 patients moved from nonfunctional ( AAOHNS class C/D) to functional (AAOHNS class A/B) categories. All patients who enjoyed postoperative hearing improvement had preoperative absence or abnormality of ABRs. No patient with normal preoperative ABR experienced he aring improvement. Hearing improvement patients also had lower preoperative caloric function on electronystagmography compared with the entire group ( p < 0.02) and were more likely to have superior vestibular nerve tumors. No differences were noted for electrical neurography and otoacoustic emission s. Conclusions: Middle fossa resection of vestibular schwannoma offers patient s the possibility of hearing improvement after treatment. The chance of hea ring improvement is significantly higher than with other forms of treatment such as radiation therapy or translabyrinthine surgery. Although preoperat ive ABR abnormality may be an indicator of poor prognosis for hearing prese rvation, those patients who enjoy hearing improvement come from the group o f patients with abnormal preoperative ABRs. Other factors identified as ass ociated with hearing improvement include poor SDS with more normal PTA,, an d significantly decreased electronystagmographic caloric function (as an in dicator of superior vestibular nerve tumors), Hearing improvement to the fu nctional range after surgical resection is possible in some patients previo usly thought to be poor candidates for hearing preservation attempts. Heari ng improvement may continue for many months after surgery.