Introduction: The Koos classification of acoustic neuromas, introduced in 1998, is a system designed to stratify these tumors based on extrameatal extension and compression of the brainstem. Grade I tumors are completely confined to the internal auditory canal. Grade II tumors have both intra- and extra-meatal components, but do not contact the brainstem. Grade III tumors make contact with the brainstem but do not compress it, while grade IV tumors cause brainstem compression. While this classification system is widely reported in the literature, to date no study has assessed the reliability of this grading system. We present an assessment of the intra- and inter-rater reliability of the Koos classification system.
Methods: A retrospective chart review was performed and the MRIs of 40 patients with acoustic schwannomas, confirmed after surgery, were selected for review. Four raters were selected to assign a Koos grade to 50 total scans (10 scans were randomly selected for test-retest). Inter- and intra-rater reliability was calculated and reported using Fleiss' kappa, Kendall's W, and Intraclass correlation (ICC).
Results: Inter-rater reliability was found to be substantial when measured using Fleiss' kappa (0.71), extremely strong using Kendall's W (0.92), and excellent as calculated by ICC (0.88).
Intra-rater reliability was perfect for three out of four raters as assessed using weighted kappa, Kendall's W and ICC, with the intra-rater agreement for the fourth rater measured as extremely high.
Conclusions: We have demonstrated that the Koos classification system for acoustic schwannoma is a reliable method for tumor classification. This study lends further support to the results of current literature using Koos grading system. Further studies are required to evaluate its validity and utility in counseling patients with regard to outcomes.
Patient Care: Conversations with the patient regarding treatment options are equally as important when it comes to counseling and prognostication. Now that the reliability of this system has been demonstrated, further studies assessing validity are warranted. We are currently working on a retrospective study correlating Koos grade to outcomes after microsurgery, radiosurgery or both. The results of this study will hopefully aid in the counseling of patients and facilitate conversations regarding treatment options and prognosis by using a uniform, reliable and valid classification system.
Learning Objectives: By the conclusion of this session, participants should be able to: 1)Describe the importance of the Koos grading scale with regard to reliability and potential validity when characterizing acoustic schwannomas. 2) Discuss, in small groups how a reliable and valid grading system can assist in counseling patients on their diagnosis and in discussing treatment options. 3) Identify the importance of reliability assessments on widely used grading scales
References: 1. Chen B, Zaebst S. In: A Macro to Calculate Kappa Statistics for Categorizations by Multiple Raters. ; 2005.
2. Anaizi AN, Gantwerker EA, Pensak ML, Theodosopoulos PV. Facial Nerve Preservation Surgery for Koos Grade 3 and 4 Vestibular Schwannomas: Neurosurgery. 2014;75(6):671-677. doi:10.1227/NEU.0000000000000547
3. Rosahl S BC. GMS | GMS Current Topics in Otorhinolaryngology - Head and Neck Surgery | Diagnostics and therapy of vestibular schwannomas – an interdisciplinary challenge. http://www.egms.de/static/en/journals/cto/2017-16/cto000142.shtml. Accessed January 22, 2018.
4. Mindermann T, Schlegel I. Grading of vestibular schwannomas and corresponding tumor volumes: ramifications for radiosurgery. Acta Neurochir. 2013;155(1):71-74. doi:10.1007/s00701-012-1553-4
5. Fischer G, Fischer C, Rémond J. Hearing preservation in acoustic neurinoma surgery. Journal of Neurosurgery. 1992;76(6):910-917. doi:10.3171/jns.1992.76.6.0910
6. Frischer JM, Gruber E, Schöffmann V, et al. Long-term outcome after Gamma Knife radiosurgery for acoustic neuroma of all Koos grades: a single-center study. Journal of Neurosurgery. March 2018:1-10. doi:10.3171/2017.8.JNS171281
7. Matthies C, Samii M. Management of 1000 Vestibular Schwannomas (Acoustic Neuromas): Clinical Presentation. Neurosurgery. 1997;40(1):1-10.
8. Kazim SF, Shamim MS, Enam SA, Bari ME. Microsurgical excisions of vestibular schwannomas: A tumor-size-based analysis of neurological outcomes and surgical complications. Surg Neurol Int. 2011;2. doi:10.4103/2152-7806.78516
9. Koos WT, Day JD, Matula C, Levy DI. Neurotopographic considerations in the microsurgical treatment of small acoustic neurinomas. Journal of Neurosurgery. 1998;88(3):506-512. doi:10.3171/jns.1998.88.3.0506
10. Kendall M, Gibbons J. Rank Correlation Methods. 5th ed. London: Edward Arnold; 1990.
11. Starnoni D, Daniel RT, Tuleasca C, George M, Levivier M, Messerer M. Systematic review and meta-analysis of the technique of subtotal resection and stereotactic radiosurgery for large vestibular schwannomas: a “nerve-centered” approach. Neurosurg Focus. 2018;44(3):E4. doi:10.3171/2017.12.FOCUS17669
12. Fleiss J. The Design and Analysis of Clinical Experiments. New York: John Wiley & Sons Inc; 1986.
13. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics. 1977;33(1):159-174.
14. Myrseth E, Møller P, Pedersen P-H, Lund-Johansen M. Vestibular Schwannoma: Surgery or Gamma Knife Radiosurgery? A Prospective, Nonrandomized Study. Neurosurgery. 2009;64(4):654-663. doi:10.1227/01.NEU.0000340684.60443.55
15. Cohen J. Weighted kappa: nominal scale agreement with provision for scaled disagreement or partial credit. Psychol Bull. 1968;70(4):213-220.