Histopathological Characteristics of Clinical Growth in Sporadic Vestibular Schwannomas

Object: Vestibular schwannomas show a large variability in growth rate, which makes prediction and anticipation of tumor growth difficult. More accurate prediction of clinical behavior requires more understanding of tumor biological factors influencing tumor progression. Biological processes like intratumoral hemorrhage, cell proliferation, vascularization, and inflammation were analyzed to determine their role in vestibular schwannoma development.

Design: Retrospective study.

Methods: Tumor specimens of 67 patients, surgically treated for a histologically proven unilateral vestibular schwannoma were studied. Preoperative MRI scans were used to determine tumor size as well as to classify tumors as homogeneous, inhomogeneous, and cystic. Immunohistochemical studies evaluated cell proliferation (Histone H3, Ki-67), vascularization (CD31), and inflammation (CD45 and CD68). Intratumoral hemorrhage was assessed by the degree of hemosiderin deposition. The expression patterns of these markers were compared with clinical aspects such as tumor size, tumor growth index, MRI appearance, patients' age, and duration of symptoms.

Results: No relation between cell proliferation and clinical tumor growth or MRI appearance was found. The degree of intratumoral bleeding, vascularization, and inflammation showed positive significant correlations with tumor size and the tumor growth index. Cystic and inhomogeneous tumors showed significantly more hemosiderin deposition than homogeneous tumors. The degree of vascularization was significantly higher in tumors with increased levels of CD68 expression.

Conclusion: The results of this study indicate that the progression of vestibular schwannomas is not based on cell proliferation alone. Factors like intratumoral bleeding, (neo-) vascularization, and the degree of inflammation might influence tumor development as well.