LAUSR

Background: A special type of meningioma is known to have infiltrated inflammatory cells within the tumor, associated with peritumoral inflammation. However, there have been no reports of meningioma with inflammatory response only around the tumor, without inflammatory cells within the tumor itself. Case Description: A 70-year-old woman presented with transient right hemiparesis due to an extra-axial tumor on the left frontal convexity. The tumor appeared hypointense on T1-weighted magnetic resonance images and hyperintense on T2-weighted images without peritumoral edema, and was homogenously enhanced associated with the peritumoral leptomeningeal enhancement. Cerebrospinal fluid examination showed an increase in the number of inflammatory cells with a predominance of mononuclear cells. During the following 1 month, the tumor size was unchanged, but the peritumoral leptomeningeal enhancement was remarkably enlarged with uncontrolled focal seizures. The tumor was subtotally removed and semisolid substances in the subarachnoid space were biopsied. Pathological examination with immunostaining revealed angiomatous meningioma: the tumor had no inflammatory cell infiltration within it, but was associated with the infiltration of immunoglobulin G4-negative lymphocytes into the border zone between the tumor and the dura mater, as well as numerous neutrophils and fibrinous exudates in the peritumoral subarachnoid space. The tumor removal rapidly improved the leptomeningeal enhancement and inflammatory reactions. Conclusion: The authors reported the first case of angiomatous meningioma associated with massive peritumoral inflammation without inflammatory infiltrates within the tumor itself.