Can Long Term hearing be Preserved after Retrosigmoid Removal of Large Vestibular Schwannoma

Hearing preservation with total/near total (T/NT) tumor removal is a worthwhile yet challenging strategy in patients with large vestibular schwannoma (VS) who have hearing before surgery.

Hearing preservation after large VS removal is challenging and the long-term outcomes of postoperatively preserved hearing have not been elucidated.

Hearing preserved after T/NT removal of large VS is maintained for a long time (>10 years), though tumor recurrence on MRI is somewhat common. Detecting small recurrence early, and regular MRI follow-up contributes to the long-term maintenance of hearing. Hearing preservation with tumor removal is a challenging yet worthwhile strategy in large VS patients with preoperative hearing.

The optimum goal of large vestibular schwannoma (VS) removal is curative tumor removal with functional preservation, especially the preservation of facial function and hearing. Though facial function is preserved at an acceptable rate, hearing preservation has proved more challenging, with disappointingly low rates of 0%–9% being reported. Several recent studies have reported relatively high rates of hearing preservation (20%–56%) after large VS removal, none established the long-term outcomes of hearing preservation.

Although improved surgical techniques and instrumentation have contributed to preserving facial function after large VS removal, the chance of hearing preservation is still low, varying from 0% to 56% among studies. Recently, a relatively high rate of hearing preservation (>20%) has been reported in several series, although the number of patients with preserved hearing in each series was ≤10. No series have reported a large number of patients in whom hearing was preserved after large VS removal.

Hearing preservation after large VS removal depends on a variety of factors, which can be classified into two groups: Those relating to patients and those relating to surgery. The former may include tumor characteristics (size, consistency, nerve of tumor origin), preoperative hearing, etc. The latter may include surgical approach and technique, intraoperative monitoring, etc. Tumor size generally affects the outcome of tumor removal, but hearing preservation is possible even in patients with giant VSs (>4 cm).

In the study by Yamakami et al, four of the six patients had a giant VS. The results showed that the postoperative hearing preservation rate was higher in cystic tumors than in solid ones, although the difference was not significant. Using cyst evacuation, a cystic tumor can be debulked much easier and in a much shorter time than a solid tumor. For this reason, tumor dissection from the cochlear nerve must be performed with more carefulness, taking more time. Furthermore, cystic VSs often grow faster than solid ones, and faster tumor growth preserves the dissecting plane between the tumor and the cochlear nerve.

In the present series, the authors showed that the hearing preserved after removal of large VS was maintained for a long time period—more than 10 years. In spite of a mild decline of PTA during the follow-up period, the annual PTA decline rate (1.26 dB/year) observed in this series was the same as that (1.2 dB/year) observed after small VS removal, and moreover, was much lower than that (3.77 dB/year) observed after radiosurgery. The mild PTA decline may represent a natural hearing decline from aging (presbycusis)

They showed that postoperatively preserved hearing was maintained for a long time, even after small CPA tumor recurrence, and that hearing was lost in the patient with IAC tumor recurrence. The major mechanism of hearing loss in patients with VS is the elevation of intracanalicular pressure caused by tumor growth in the IAC, not in the CPA. Therefore, small CPA tumor recurrence not extending into the IAC does not affect postoperatively preserved hearing. The small CPA tumor recurrences in the present series were well controlled non-surgically, either by the GK or by the observation only.

The study showed that the hearing preserved after retrosigmoid T/NT removal of large VS was maintained for a long time of more than 10 years, though tumor recurrence was somewhat common, and long-term follow-up using regular MRI enabled early diagnosis of tumor recurrence, which was controlled non-surgically.

Reference : Long-Term Outcomes of Hearing Preservation After Retrosigmoid Removal of Large Vestibular Schwannoma

Neurology India

Iwao Yamakami, Shunsuke Kubota, Yoshinori Higuchi, Toru Serizawa

DOI: 10.4103/0028-3886.375385