Glossopharyngeal schwannomas: a 100 year review.

OBJECTIVES To review the literature on glossopharyngeal schwannomas with a focus on clinical presentation, radiologic/audiologic characteristics, and management options, and to propose a mechanism explaining the nature of vestibulocochlear dysfunction seen with these tumors. STUDY DESIGN Contemporary review. METHODS English literature search for cases of primary isolated glossopharyngeal schwannomas and chart review of two new cases. RESULTS A total of 42 glossopharyngeal schwannoma cases between 1908-2008 were reviewed. Of these 84% presented with vestibulocochlear symptoms whereas only 30% presented with glossopharyngeal symptoms. Tumors can occur anywhere along the CNIX; however, the majority of symptomatic cases are intracranial/intraosseous, which present with vestibulocochlear dysfunction. Reviewed cases typically described the caliber of CNVII and VIII on CT/MRI as normal. We present a case where notching and displacement of CNVIII by the tumor can be appreciated on MRI, allowing for the first correlation between clinical symptoms and imaging findings. Mid frequency SNHL was prevalent in contrast to the high-frequency pattern typical of vestibular schwannomas. Tonotopic studies of CNVIII mapped low-to-mid frequency fibers along the posterior medial surface corresponding to the area of greatest compression by glossopharyngeal schwannomas. CONCLUSION Glossopharyngeal schwannomas usually present with vestibulocochlear rather than glossopharyngeal symptoms, likely due to CNVIII compression and displacement by tumor, which can be better appreciated with modern imaging. The tumor's location posterior and medial to CNVIII combined with the complex CNVIII tonotopic organization may account for the preferential mid-frequency hearing loss seen in these patients.