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Related Experiment Video

Updated: Jun 16, 2026

A Unified Methodological Framework for Vestibular Schwannoma Research
08:43

A Unified Methodological Framework for Vestibular Schwannoma Research

Published on: June 20, 2017

Surgical Outcomes in Large Vestibular Schwannomas: Proposed Koos Grade V and Radiological Risk Features.

Ken Matsushima1, Michihiro Kohno1, Kyosuke Matsunaga1

  • 1Department of Neurosurgery, Tokyo Medical University, Tokyo, Japan.

Operative Neurosurgery (Hagerstown, Md.)
|June 15, 2026
PubMed
Summary

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A new Koos grade V subclassification for large vestibular schwannomas (VSs) effectively identifies high-risk tumors. This refined grading improves prediction of complications and need for further treatment after surgery.

Area of Science:

  • Neurosurgery
  • Otolaryngology
  • Neurosurgical Oncology

Background:

  • Surgery for large vestibular schwannomas (VSs) demands high safety and durable tumor control.
  • The current Koos grading system has limitations in stratifying risk within grade IV VSs.
  • A need exists for improved risk stratification in managing large VSs.

Purpose of the Study:

  • To evaluate a proposed Koos grade V subclassification for large VSs.
  • To determine if Koos grade V improves risk stratification for perioperative complications and facial nerve outcomes.
  • To assess the long-term need for additional treatment in VS patients using the proposed grade V.

Main Methods:

  • Retrospective analysis of 435 patients with Koos grade III-V VSs undergoing primary microsurgical resection (2016-2020).
Keywords:
Acoustic neuromaCerebellopontine angleFacial nerve palsyFunctional preservationHearing lossSkull base tumor

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Last Updated: Jun 16, 2026

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  • Assessment of preoperative tumor size and radiological risk features (edema, ventricular enlargement, hypervascularity).
  • Time-to-event and multivariable analyses were performed for Koos grades IV-V tumors.

    • Main Results:

    • Proposed Koos grade V demonstrated clustered radiological risk features and higher rates of major perioperative complications (16.9%) compared to grade IV.
    • Despite high resection rates (95.0% in grade V), the need for additional treatment (stereotactic radiosurgery/reoperation) increased stepwise, reaching 28.1% in grade V.
    • Favorable facial nerve function was maintained (~95%) across all grades, and hypervascularity strongly predicted complications.

    Conclusions:

    • The proposed Koos grade V, defined by midline extension, is a simple and reproducible method for identifying high-risk large VSs.
    • This subclassification aids in predicting adverse imaging features, increased complication rates, and greater long-term need for additional treatment.
    • The proposed grade V maintains high resection rates and favorable facial nerve outcomes, enhancing surgical management strategies for large VSs.