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Neurofibromatosis 2 Invasion of the Internal Auditory Canal Wall: Clinical Significance

Doherty, Joni*; Go, John L.; Linthicum, Fred H. Jr.*

doi: 10.1097/MAO.0000000000000494
Tumors of the Ear & Cranial Base
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Objective To describe the infiltration of severe phenotype (“Wishart”) neurofibromatosis type 2 (NF2)–related vestibular nerve schwannomas (VSs) into the internal auditory canal wall in contrast to sporadic VS and the milder (“Gardner”) phenotype NF2-related VS.

Study Design Retrospective case series involving microscopic examination and review of clinical history.

Setting Temporal bone laboratory, harboring 849 documented pairs of decalcified, formalin-fixed, celloidin-embedded, sectioned human temporal bones (hTBs) with clinical history.

Subjects and Methods Histologic sections from 56 patients who had been treated by the House Clinic for VS and who had pledged their temporal bones were identified in the data base of the laboratory. Twenty-four hTBs were from individuals with NF2.

Each series of sections was examined microscopically for evidence of invasion of the walls of the internal auditory canal (IAC), hearing thresholds, speech discrimination, score (SDS), and tumor recurrence.

Results Infiltration of the walls of the IAC by small buds of VS was found in 17 of the 24 NF2 hTBs. The only 2 NF2 without invasion were from an elderly patient with the milder (Gardner) form of NF2. Ten of the 12 NF2 patients had undergone surgery for the removal of their tumor, but residual tumor remained in the bone surrounding the IAC. Invasive VS were associated with poorer hearing thresholds at 250, 500, 1,000, and 2,000 Hz and lower SDS score. A relationship between invasion and recurrence was not statistically significant.

Conclusion The majority of IAC tumors associated with the severe “Wishart” phenotype demonstrate bone invasion within the IAC. Invasion of bone was associated with poorer hearing. The invasive nature of NF2-associated tumors may partially explain their higher recurrence rate after resection. Surgeons managing NF2-related VS should be aware of the small infiltrations of the wall of the IAC when removing these tumors to minimize recurrence.

*The House Temporal Bone Laboratory, University of California; and †Department of Radiology, University of Southern California, Los Angeles, California, U.S.A.

Address correspondence and reprint requests to Fred H. Linthicum Jr., M.D., 2100 West 3rd Street, Los Angeles, California; E-mail: flinthicum@mednet.ucla.edu

The authors disclose no conflicts of interest.

Supported by NIDCD.NIH U24 DC 011962.

Copyright © 2014 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company