Microhemorrhage, a possible mechanism for cyst formation in vestibular schwannomas

Cystic vestibular schwannoma (VS) is a unique subgroup of VSs characterized by unpredictable expansion of the cyst component. Little is known, however, about the mechanism of cyst formation. In this study the authors compared neuroimaging and histological characteristics of cystic with solid VS to determine the pathogenesis of the cystic subgroup. Two cohorts, one comprising 10 patients with cystic VS and the other comprising 10 patients with solid VS, were studied. Surgery was chosen as the primary treatment in all patients, with no other modality applied. Preoperative magnetic resonance images and histological characteristics of the tumor in patients with cystic VSs were evaluated and compared with those in the group with solid VSs. Differences between the two groups were assessed using the chi-square test. Neuroimaging findings revealed that either fluid-fluid level or hemosiderin deposit was present in all cystic VSs. Histological evidence of microhemorrhage, such as hemosiderin-laden macrophages (p = 0.069), hemosiderin deposits (p = 0.019), thrombotic vessels (p = 0.008), and abnormal vessel proliferation (p = 0.006) were more prominent in cystic VSs compared with solid ones. There was no difference in Antoni type dominance and Ki-67 proliferative index between the two groups. Intratumoral microhemorrhage is a possible mechanism of pathogenesis in cystic VS.