gms | German Medical Science

ESBS 2005: Skull Base Surgery: An Interdisciplinary Challenge
7th Congress of the European Skull Base Society held in association with
the 13th Congress of the German Society of Skull Base Surgery

18. - 21.05.2005, Fulda, Germany

Surgical considerations in cerebello-pontine angle (CPA) meningiomas involving the internal auditory canal (IAC)

Meeting Contribution

  • F. Roser - Dept. of Neurosurgery, University of Tübingen, Tübingen, Germany
  • M. Nakamura
  • P. Vorkapic
  • M. Samii - Department of Neurosurgery, International Neuroscience Institute, Hannover, Germany
  • M. Tatagiba - Dept. of Neurosurgery, University of Tübingen, Tübingen, Germany

ESBS 2005: Skull Base Surgery: An Interdisciplinary Challenge. 7th Congress of the European Skull Base Society held in association with the 13th Congress of the German Society of Skull Base Surgery. Fulda, 18.-21.05.2005. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc05esbs33

DOI: 10.3205/05esbs33, URN: urn:nbn:de:0183-05esbs333

Published: January 27, 2009

© 2009 Roser et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en). You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.


Outline

Text

Introduction

Among all different classification systems that have been proposed for CPA meningiomas, there was no attention paid to those extending into the IAC or originating from the IAC, which we found to be of high influence on surgery and clinical outcome [1], [7]. We conducted the study to distinguish the impact of either primary dural involvement of the meningioma in the IAC or secondary extensive growth into the IAC. We discuss cases with dural insertion in/at the IAC or cranial nerve (CN) infiltration of the meningioma.

Material and methods

The presented study group consists of 74 patients with histological and radiological confirmation of a CPA meningioma with dural involvement of the IAC. The pre- and postoperative facial nerve function was examined according to the House & Brackmann grading system [4]. Pre- and postoperative hearing function was graded according to the Hannover Classification System in steps of 20 dB hearing loss, calculated as the mean of air conduction data at 1, 1.5, 2, and 3 kHz in the PTA. Additionally charts of the patients including surgical and clinical records, intra-operative auditory evoked potentials and imaging studies were reviewed.

Results

The site of dural origin could be determined intraoperatively in 55 patients, showing insertion of the CPA-meningioma in/at the IAC in 36%, ventral to the IAC in 23.6%, inferior and superior to the IAC in each 16.4% and dorsal to the IAC in 7.3% of cases (Figure 1 [Fig. 1]). Total resection has been achieved in 86.1%. 34 patients needed opening of the IAC for total removal; this procedure did not influence the functional outcome. Patients with secondary involvement of the IAC had anatomical preservation of the facial and cochlear nerve in 94%, whereas patients with dural insertion in the IAC of 80% resp. 75%. Functional preservation of CN VII/VIII in cases of tumour extension within the IAC was 86%/77%, in the IAC-involved group only in 60%. Sacrifice of the petrosal vein significantly contributed to the surgical morbidity of the patients (cerebellar edema and bleeding, Peduncular hallucinosis). Multiple or longer than 5 min lasting acoustic-evoked-potential-phase decreases inherit a 75% risk of hearing loss. Due to involvement of the IAC in all cases in this cohort, the differentiation to vestibular schwannoma was not obvious in all cases: Widening of the IAC with bony erosion, cystic degeneration of the tumour or pure globoid shape of the tumour without dural attachment has been seen in infrequently.

Conclusion

Meningiomas of the CPA involving the IAC need special surgical management. The clinical outcome depends almost exclusively on the biological behavior of the tumor, as we demonstrated with comparisons of patients with secondary IAC involvement and different surgical approach (opening vs. intact IAC) or different tumour extension (ventral vs. dorsal to the IAC). The skills and experience of the surgeon must be appropriate in a way that the outcome should not depend on the necessary drilling procedures at the IAC [8].

In the majority of the cases, dural origin within the IAC implied infiltrative or at least strong adhesive nature of the meningioma. Ischemic events of the cochlear nerve or shared vascular supply at the tumor-nerve border, as well as microscopic invasion of the cochlear nerve itself may be responsible for the far inferior clinical outcome in cases with IAC-involvement compared to other CPA meningiomas [2], [3]. Facial and cochlear nerve functional outcome reflected this fact in a reliable way.

Presence and absence of acoustic evoked potentials in surgery of CPA meningiomas reliably predicted presence and absence of postoperative auditory function. Intermittent deterioration of ABRs may result in postoperative deafness depending on the duration of these events during surgery. Hearing improvement is only seen when the ABRs are stable for amplitudes and latencies throughout surgery [5], [6].

Dural involvement of the IAC requires its opening by diamond drill. Drilling and opening the IAC per se as part of a surgical procedure does not influence the outcome of facial or cochlear nerve function.

The increased cranial nerve morbidity is attributed to the infiltrative behavior of these meningiomas. If affected nerve segments have to be sacrificed, immediate reconstruction enables satisfactory long-term results.


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