Growth of sporadic vestibular schwannomas correlates with Ki-67 proliferation index

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Sporadic vestibular schwannoma show a wide variability of their growth rate. Some tumors might remain quiescent for a long time without symptoms and other tumors might suddenly enlarge. Sometimes during surgical removal of tumors, it is useful to have a parameter for the prediction of the further growth potential of the schwannoma, especially if tumor resection results in functional impairment of the facial nerve. An often used histological parameter for growth rate of tumor cells is the proliferation index. In our study we observed a series of 50 patients with neurinoma of the vestibular nerve by "wait and scan". After the first magnetic resonance imaging (MRI) all patients were controlled by a second MRI. The time between the MRIs ranged between 3 and 26 months (median 9). In 45 of 50 patients a surgical removal of the tumor by transtemporal approach followed. The proliferation index (Ki-67) was identified in the histological tumor specimens. The next step was the correlation of proliferation index and "tumor doubling time" (TDT). The volume of the tumors was provided by measuring three diameters of the tumors in MRI and calculating the volume with a formula. The volume of the tumors were used to calculate tumor growth and TDT. 10 patients showed no tumor growth during follow up. The average TDT in 40 cases was 22 months (SD 16). In 33 cases we were able to determine a proliferation index, which showed an average score of 1.99 %. Statistical analysis showed a correlation between proliferation index and TDT with a coefficient of - 0.42 (s: 0.014). In two cases with relevant clinical tumor growth (TDT: 12 months), the MIB-1 index was nearly 0 % in different areas of the tumor specimen. May be in these cases, the cell proliferation declined just before operation. On the other hand we found one patient with a high proliferation index of 3.3 % and a rather long TDT of 19 months. The determination of proliferation can serve as a further decision guidance during surgery of vestibular schwannoma.