Vestibular schwannomas: Correlations between magnetic resonance imaging and histopathologic appearance

Background: The indication for surgery of vestibular schwannomas (VS) remai ns controversial and depends on several factors. The ability to predict the ir patterns of growth would allow better surgical planning. This, growth ma y depend on tumoral proliferation but also depends on dystrophic changes. Objective: The aim of this study was to evaluate the role of magnetic reson ance imaging (MRI) in predicting the evolution of VS. For this purpose, the authors attempted (I) to compare the MRI appearance of VS with its histopa thologic features, (?) to correlate the MRI appearance of VS and its histop athologic features with its sire, and (3) to evaluate the index of prolifer ation (IP) of each VS. Patients and Methods: Thirty VS were studied with MRI before surgery. The V S were measured and classified as homogeneous, heterogeneous, and cystic. A fter surgery, IP was evaluated with immunohistochemical study using MIB-1 m onoclonal antibody. and compared with tumor sire. Pathologic studies evalua ted the prevalence of Antoni type A and type B tissue, the amount of fibros is, and the presence of siderin-loaded macrophages, xanthomatous cells, and cysts. Results: The IP was low (0.2%-2.2%) and was not correlated with VS size. On MRI, 13 VS were homogeneous. 12 heterogeneous. and 5 cystic. The 13 homoge neous VS were smaller and wen predominantly made of Antoni type A tissue. T he 12 heterogeneous and 5 cystic VS were larger and were predominantly made of Antoni type B/mixed tissue. Heterogeneous and cystic VS showed signific antly more hemosiderin deposits. There was a significant relation between t he amount of hemosiderin deposits and the mean size of VS. Microscopic cyst s were observed only in VS with cystic MRI appearance. Fibrosis was present in all tumors regardless of their size and MRI appearance. Conclusion: A heterogeneous MRI aspect (correlated with larger mean size) n ot only is related to the ratio of type A to type B tissue but also is caus ed by other pathologic changes, mainly hemosiderin deposits and cystic form ation. Increasing tumor sire probably depends less on IP than on dystrophic changes (hemosiderin, cysts) and/or on the presence of type B tissue.