The Solid Component of Radiographically Non-Growing, Post-Radiated Vestibular Schwannoma Retains Proliferative Capacity

Objective: Nearly all radiated vestibular schwannomas (VS) have solid tissue remaining at the radiation bed. The viability and proliferation capacity of this tissue has never been objectively assessed. The goals of our study were to (1) determine whether this tissue retains the morphological and immunohistochemical features of VS and (2) evaluate whether the tissue is capable of proliferation in cell culture. Methods: Case history, magnetic resonance imaging (MRI), cell culture, histology, and immunohistochemistry. Results: We report the first case of a post-radiated, sporadic VS patient whose non-growing, residual MR-enhancing solid tissue was examined histologically and in cell culture. These cells were architecturally identical to non-radiated VS, had a Ki67 proliferative index similar to non-radiated sporadic and NF2-associated VS, were S100 positive, and grew in culture with kinetics comparable to non-radiated VS. Conclusion: The long-term risk for delayed tumor growth and/or secondary malignancy in radiated VS patients is unknown. Because the average life span in the United States is nearly 80 years, patients should be informed that (1) residual VS cells are viable even when tumors appear to be non-growing on MRI, (2) post-radiation surveillance imaging is required indefinitely, and (3) radiation may incur more risk in those patients with life expectancy >20-25 years.