Neurooncology of Benign Central and Peripheral Nervous System Tumors

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This ongoing natural history study has resulted in significant improvements in the understanding how NF2 affects patients. We found that central nervous system tumors in NF2 demonstrate a stepwise growth pattern. We also found that these tumors are made of many different populations of tumor cells. These findings emphasize the need for long term follow up of patients with NF2 to evaluate disease progression. Patients with NF2 have symptoms that significantly affect their lives such as hearing loss and speech/swallowing dysfunction. This natural history study has helped us understand how these symptoms arise even when the tumors are very small or quiescent. These findings will help clinicians find better ways to prevent hearing loss and to counsel patients about speech and swallowing problems. We now hope to understand the biologic basis for speech and swallowing dysfunction in patients with NF2. We will study and report the strength of association of MRI findings, clinical assessments cranial nerve deficits and speech/swallowing dysfunction. We hope to identify imaging biomarkers of hearing loss in NF2. We will attempt to discover the mode of peripheral neuropathy in patients with NF2. Lastly, we will attempt to discover previously unknown serum biomarkers associated with high tumor burden in NF2. Using the current cohort of subjects with NF2, we confirmed the presence of increased protein within perilymph by MRI imaging as FLAIR hyperintensity.36 In this cross sectional study, a close correlation between increased protein and hearing loss was demonstrated. This study validated MRI imaging as a method to detect increased protein within perilymph, and as a marker for hearing loss. We now have a convenient, non-invasive tool for monitoring of perilymph protein content. MRI imaging can be performed repeatedly and over long periods to detect changes in perilymph protein with time and with changes in hearing. In another analysis, we found that a large proportion of patients with NF2 report speech and swallow deficits that are not evident on objective measurements. We also found hypoglossal neuropathy unrelated to prior surgical interventions. Our findings suggest that swallowing and speech in problems in NF2 are associated with lower cranial nerve neuropathy, some due to compressive effects of posterior fossa tumors. We found that patients with NF2 present with neuropathy related to peripheral nerve schwannomas as well as unexplained EMG/NCS findings. In instances of distinct schwannoma growth along peripheral nerves, nerve fascicle sparing surgical resection leads to resolution of neuropathic symptoms. EMG/NCS studies and imaging helps guide the management of NF2 patients with high degree of certainty.