Immunohistochemical expression of thrombomodulin in vestibular schwannoma.

Many vestibular schwannomas (VS) manifest intratumoral microhemorrhages whose underlying mechanisms are not fully understood. Thrombomodulin (TM) is an endothelial anticoagulant cofactor that promotes the thrombin-mediated formation of activated protein C that inhibits thrombus formation. We investigated the existence of TM in VS and its potential role in the development of microhemorrhages. We used immunohistochemical staining to study the expression of TM in tissues derived from 25 patients with VS. Hemosiderin deposition was examined by Berlin blue staining and compared with the expression of TM. Vascular endothelial cells in all 25 VS tissues expressed TM. The TM-positive vessel ratio, calculated by dividing the number of TM-positive by the number of CD34-positive lumens, was significantly higher in hemosiderin-laden than hemosiderin-negative tissues (0.71 ± 0.17 vs. 0.53 ± 0.31, p = 0.049, Mann-Whitney U test). Our findings suggest a close relationship between the expression of TM and microhemorrhage in VS.