To critically analyze each reported case of malignant transformation of vestibular schwannoma (VS) after either stereotactic radiosurgery (SRS) or microsurgery (MS).
We searched the Pubmed/Medline database using the relevant key words vestibular schwannoma, acoustic neuroma, malignant, transformation, radiation, induced, stereotactic, radiosurgery, malignancy, GammaKnife, and CyberKnife and combinations thereof.
Inclusion criteria for malignant transformation of VS after SRS included histopathology of initially benign VS, subsequent histopathology confirming malignant VS, reasonable latency period between malignancy and benign diagnoses.
A neurotologist and a skull base neurosurgeon independently assessed each case report for quality, entry, exclusion criteria, and comparability of extracted data.
We calculated median age, latency times, and survival times for each case report.
Malignant transformation has been documented to occur after either SRS or MS. Eight cases were included that showed histopathologic evidence of malignant transformation after SRS and MS. Four cases of malignant transformation were included that demonstrated malignant transformation after MS only. Malignant transformation of VS can also occur de novo, and de novo malignant VSs are also encountered, which can confound a causal inference from either SRS or MS. Eighteen cases of primary malignant VS were included. Studies that were identified but not included in the review are summarized and tabulated. We found 12 studies of malignant transformation associated with NF2.
The potential mechanism leading to malignant transformation of VS seems more obvious for SRS and is less understood for MS. Given a low incidence of de novo malignant schwannoma, the possibility that these are spontaneous events in either setting cannot be ruled out. Risk of malignant transformation of VS after either SRS or MS is not zero; however, the magnitude of this risk is probably minimal based on the evidence from eight histopathologically confirmed cases.
*Division of Neurotology and Skull Base Surgery, Department of Otolaryngology–Head and Neck Surgery, †Division of Neurological Surgery, Department of Surgery, School of Medicine, and ‡Department of Biomedical Engineering, School of Engineering, University of California, Irvine, California, U.S.A.
Address correspondence and reprint requests to Hamid R. Djalilian, M.D., Director, Division of Otology, Neurotology and Skull Base Surgery, Department of Otolaryngology–Head and Neck Surgery, University of California Irvine, Otolaryngology-5386, 19182 Jamboree Rd, Irvine, CA 92697, U.S.A.; E-mail: firstname.lastname@example.org
The authors disclose no conflicts of interest.
Presented at the 2014 Combined Otolaryngology Sections Meeting, May 14–17, 2014, Las Vegas, NV, U.S.A.
M. M. M. and Y. G. contributed equally to this article.