An Underlying Pathological Mechanism of Meningiomas with Intratumoral Hemorrhage: Undifferentiated Microvessels

BackgroundMeningiomas usually present with a gradual onset of symptoms, and their acute presentation with a hemorrhagic event appears to be a rare condition. Although many clinical features of such a condition have been characterized, pathophysiological mechanisms underlying the bleeding remain unclear, and some contradictory results have been reported. The value of tumor vascularity as an index for the bleeding propensity of meningiomas is inconsistent. We sought to identify whether meningiomas have different types of blood vessels, and to explore the association of the different tumor vessels with intratumoral hemorrhage.MethodsSix patients with meningioma with acute onset due to intratumoral hemorrhage were identified, and 12 nonhemorrhagic meningiomas were matched according to specific clinical data. The characteristics of tumor vessels were examined through immunohistochemical staining of CD31, CD34, and smooth muscle actin (SMA). The number of stained vessels was counted and compared between the 2 groups.ResultsTwo distinct types of blood vessels were determined in all meningiomas: undifferentiated (CD31+/CD34−) and differentiated (CD31+/CD34+) vessels, and most differentiated vessels were covered by pericytes marked by SMA. However, only the mean number of undifferentiated vessels in hemorrhagic meningiomas was significantly higher than that in controls (15.3 ± 4.9 vs. 6.4 ± 3.6; P < 0.01). Neither the number of differentiated vessels nor the total number of tumor vessels were significantly different between the 2 groups (P > 0.05).ConclusionsOur results suggest that tumor vasculature in meningiomas is heterogeneous, and that the undifferentiated vessels may play a pivotal role in the spontaneous intratumoral hemorrhage from meningiomas.