Vestibular schwannomas and auditory function: options in large T3 and T4 tumors?

While hearing preservation has become an accepted treatment goal, there are still major doubts whether and to what extent this aim is feasible in large tumors that cover the auditory nerve and involve the brainstem.

One thousand eight hundred (1,800) vestibular schwannomas (VS) were operated on at Nordstadt Neurosurgical Department from 1978 to 1999 by the senior surgeon (MS). There were 1,800 tumors in 1,750 patients, 1,605 patients had unilateral tumors, 145 patients had neurofibromatosis type 2 with bilateral tumors, 195 of which were treated surgically in our unit. Preservation of the cochlear nerve was attempted when ever possible. The audiometric data are analyzed by Hannover Classification System graded in steps of 20 dB by audiometry and in steps of 10% to 30% by speech discrimination. Those data were set into relation with the Hannover tumor extension grading T1 to T4.

Overall preservation rate was 40% with considerable differences, though, depending on the preoperative hearing quality and the tumor extension. Best results were obtained for intrameatal tumors (T1) with 56% and small intra-extrameatal tumors (T2) with 57% preservation rate. While preservation rate was at 44% in medium-sized tumors (T3), it was at 20% for T4 tumors with brainstem compression or even dislocation. However, satisfactory chances were encountered in cases with normal or good preoperative hearing, on average 54%, specifically 71% in T1, 69% in T2, 58% in T3 and 29% in T4. Regarding the quality of the preserved hearing, up to one third of cases in T1 and T2 may retain their preoperative hearing level, while this ranges around 20% for T3 and 10% to 14% in T4 tumors.

For long, hearing preservation in medium sized or large tumors has not received any attention because of the presumed lack of realistic chances and the expected bad quality. Obviously, hearing preservation may be achieved in relevant numbers and at satisfactory quality levels. This aspects appears important to be addressed further in view of the fact that over 70% of tumors are presented for surgery at T3 or T4 extensions.

The summit of hearing preservation has not been reached as improvements are still achieved even in most difficult conditions.