Hearing preservation surgery for vestibular schwannomas via the retrosigmoid transmeatal approach: surgical tips

Masahiko Wanibuchi; Takanori Fukushima; Allan H. Friedman; Kentaro Watanabe; Yukinori Akiyama; Takeshi Mikami; Satoshi Iihoshi; Tomohiro Murakami; Toshiya Sugino; Nobuhiro Mikuni

doi:10.1007/s10143-014-0543-9

Neurosurgical Review

July 2014, Volume 37, Issue 3, pp 431–444 | Cite as

Hearing preservation surgery for vestibular schwannomas via the retrosigmoid transmeatal approach: surgical tips

Authors
Authors and affiliations

Masahiko WanibuchiEmail author
Takanori Fukushima
Allan H. Friedman
Kentaro Watanabe
Yukinori Akiyama
Takeshi Mikami
Satoshi Iihoshi
Tomohiro Murakami
Toshiya Sugino
Nobuhiro Mikuni

Original Article

First Online: 22 April 2014

Received: 28 February 2013

Revised: 25 November 2013

Accepted: 19 January 2014

Abstract

Maximum tumor extirpation with preservation of the facial and cochlear nerve function is the goal of surgery for vestibular schwannoma. To preserve cochlear nerve function, the surgeon must employ a detailed knowledge of microanatomy, precise microsurgical techniques, and persistence. This paper describes the “pearls” of surgical techniques based on the anatomical study inside the mastoid from the view of the retrosigmoid transmeatal approach. A total of 592 consecutive patients underwent surgical removal of unilateral vestibular schwannoma (VS) between January 1994 and December 2009. The hearing preservation rate was 53.7 % for large vestibular schwannomas (>20 mm in diameter) and 74.1 % for tumors of all sizes. The key procedures for hearing preservation surgery are as follows: bloodless microdissection, sufficient coring-debulking, capsular elevation to locate the facial and cochlear nerves both electrophysiologically and by visual observation, sharp dissection of the facial and cochlear nerves, and avoidance of heat and mechanical injury to the nerves, the internal auditory artery, and the brain stem. Besides these techniques, appropriate instruments are essential to preserve hearing. The function of the facial and cochlear nerves should be the foremost concern. Meticulous techniques and the knowledge of microsurgical anatomy lead to hearing preservation with maximum tumor removal.

Keywords

Acoustic neuroma Cerebellopontine angle tumor Hearing preservation Microsurgery Retrosigmoid transmeatal approach Vestibular schwannoma

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Notes

Comments

Venelin Gerganov, Hannover, Germany

The authors of this nicely written manuscript present their technique for function-preserving vestibular schwannoma surgery. Using this technique in a relatively large series of patients, they could achieve excellent functional results: the hearing preservation rate was 54 % for vestibular schwannomas >20 mm and 74 % for tumors of all sizes. The facial nerve functional outcome corresponds also to the highest current treatment standards. One should highlight explicitly their surgical philosophy, which I completely share: the patient’s preoperative hearing level is the sole criterion for attempting hearing preservation surgery and the size of the tumor is irrelevant.

Whatever operative technique one applies in his practice, the detailed description of the technique developed and used by the senior authors, is highly valuable. It does not differ essentially from the operative technique that we use (developed by M. Samii). Still, there are some minor differences, such as the preoperative placement of spinal drainage catheter, the dural incision, or the closure of the internal auditory canal (IAC). Other differences are more important and need to be mentioned.

We prefer the semisitting positioning of the patient, which allows for two-hand tumor dissection because there is no need for constant suction. Moreover, this position obviates the need for frequent bipolar coagulation that may be very dangerous for the nervous structures. In this point, I disagree with the view of the authors on the necessity to keep a “bloodless surgical field.” Only the major bleeding arteries need to be coagulated. The blood is “washed-out” by irrigation, and the CSF, blood, and fluids drain out spontaneously.

We prefer to open the IAC prior to tumor debulking (with the exception of giant VS) thereby avoiding the spread of bone dust. Importantly, the canal should always be widely opened—for approximately 180°—in order to provide an unobstructed view to the tumor. The extent of lateral opening, however, is determined by the tumor extension, which is assessed at surgery: the preoperative MR imaging may be misleading in this regard.

The constant auditory brain stem monitoring is essential because it provides constant feedback on the cochlear nerve function. Thus, surgical manipulations and actions could be modified accordingly.

Once the intracanalicular tumor portion is removed, the extracanalicular is approached. Tumor debulking should proceed systematically in all directions. Then, the remaining tumor part is pulled slightly into the operative field and its capsule is dissected in the arachnoid plane. In larger VS, these steps are repeated alternatively in all directions. The dissection of the nerves should always be performed in the arachnoid plane, usually by using just two instruments: to hold the tumor capsule and to pealing off the arachnoid. Thus, the microvasculature running in the arachnoid that is essential for the hearing can be preserved.

At the end, we plug the IAC with fat pieces harvested from the incisional area and seal them with fibrin glue.

Ricardo Ramina and Luis Fernando M Silva, Curitiba, Brazil

The authors describe step-by-step tips for preservation of the cochlear nerve function in a large series of 592 unilateral vestibular schwannomas. The retrosigmoid transmeatal approach was used in 70 % of the cases. Maximum tumor removal with preservation of facial and cochlear nerve function was the aim of surgery. Hearing preservation was attempted in patients with preoperative hearing levels of class A, B, C, or D (pure tone average (PTA) <60 dB and speech discrimination score (SDS) >50 %). They emphasizes the importance of intraoperative monitoring, not opening the vestibule or the posterior semicircular canal during drilling the wall of the IAC, and sharp dissection of the nerves avoiding heat and mechanical injury. Employing these surgical strategies, the authors achieved a high rate of hearing preservation (74.1 %) for tumors of all sizes and 53.7 % for large vestibular schwannomas (>20 mm in diameter). However, gross total removal was performed in only 74.6 % of cases. Functional facial nerve preservation (grades I and II on the House–Brackmann scale) was 90.7 % for large tumors and 92.7 % for tumors of all sizes. CSF leak was observed in 3 of 54 patients with larger tumors. No mortality associated with the surgery was reported. This article highlights the importance of functional preservation of the involved cranial nerves in vestibular schwannomas surgery and provides valuable surgical tips for hearing preservation.

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Authors and Affiliations

Masahiko Wanibuchi
- 1
Email author
Takanori Fukushima
- 2
- 3
Allan H. Friedman
- 2
Kentaro Watanabe
- 2
- 3
Yukinori Akiyama
- 1
Takeshi Mikami
- 1
Satoshi Iihoshi
- 1
Tomohiro Murakami
- 1
Toshiya Sugino
- 1
Nobuhiro Mikuni
- 1

1.Department of NeurosurgerySapporo Medical University School of MedicineSapporoJapan
2.Division of NeurosurgeryDuke University Medical CenterDurhamUSA
3.Carolina Neuroscience InstituteRaleighUSA

Hearing preservation surgery for vestibular schwannomas via the retrosigmoid transmeatal approach: surgical tips

Abstract

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