Gamma knife radiosurgery for vestibular schwannoma: early hearing outcomes and evaluation of the cochlear dose.

OBJECTIVE: To evaluate the hearing outcomes for a group of unilateral vestibular schwannoma patients treated with gamma knife radiosurgery and to determine if the cochlear radiation dose affects hearing outcome measures. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: Vestibular schwannoma patients (n = 33) treated with gamma knife with complete audiometric follow-up. INTERVENTION: Gamma knife radiosurgery and audiometry. MAIN OUTCOME MEASURES: Pure-tone average (PTA), speech discrimination score (SDS), and cochlear radiation dose. RESULTS: The median audiometric follow-up was 24 months, with a range of 6 to 51 months (mean, 24.6 mo; standard deviation [SD], 13.9). Thirty-one patients received a maximum radiation dose of 26 Gy, and 2 received 24 Gy (mean, 25.9 Gy; SD, 0.48). All patients were treated to the 50% isodose line, and the prescription isodose was 13 Gy in 31 patients and 12 Gy in 2 patients (mean, 12.9 Gy; SD, 0.24). Mean pretreatment PTA and SDS were 55.86 dB and 45.70%, respectively. Mean PTA and SDS at last follow-up were 66.55 dB and 39.15%, respectively. The PTA at 6 months (p = 0.003), 12 months (p = 0.004), and last follow-up (p = 0.001) was significantly poorer than the pretreatment PTA. There was no significant difference between pretreatment and follow-up SDS at any time interval. The mean cochlear radiation dose was 5.2 Gy (range, 2.6-8.5 Gy). The median cochlear dose was 4.75 Gy. Fifteen patients received less than the median cochlear dose, and 18 received greater than or equal to the median cochlear dose. The change in PTA from baseline was significantly poorer at 12 months for those patients whose cochlea received 4.75 Gy (p = 0.02) or greater. Stepwise linear regression analysis using the variables of minimum SDS subsequent to baseline SDS versus total cochlear dose revealed a negative correlation (p = 0.012)-as total cochlear dose increased, SDS decreased. CONCLUSION: The PTA was significantly worse after gamma knife radiosurgery, with a mean follow-up of 24.6 months. Higher radiation doses to the cochlear volume negatively impacted hearing outcomes after radiosurgery for this group of vestibular schwannoma patients.

Middle ear injury through the external auditory canal: a review of 44 cases.

We performed a retrospective review of 44 patients with middle ear injury incurred through the external auditory canal. Twenty-two of the 44 patients had presented to our center within 1 month of their injury (early group), and 22 presented later (delayed group); the mean interval from the time of the trauma to presentation was 6 days in the early group and 7 years in the delayed group. The causes of injury were penetrating trauma (70% of cases), thermal insults (20%), and explosive and nonexplosive blasts (9%). Purulent otorrhea, cholesteatoma, and ossicular discontinuity were more common in the delayed group. Otologic surgery was required in 9 early-group patients (41%) and in all 22 delayed-group patients (100%). Two patients in the early group developed a dead ear. The mean pure-tone averages (PTAs) at presentation were 30.7 and 52.2 dB in the early and delayed groups, respectively; after management, the corresponding mean PTAs were 21.0 and 42.5 dB. The respective mean air-bone gaps in the two groups were 14.6 and 28.2 dB at presentation and 8.0 and 17.2 dB after management. We conclude that middle ear injury incurred as a result of trauma sustained through the external auditory canal is associated with considerable morbidity. Patients who present in a delayed fashion have significantly poorer hearing at presentation and after management. Patients who do not develop a dead ear generally derive benefit from reconstruction of the middle ear sound-conduction mechanism.