A meningioma with peripheral rim enhancement on MRI.

Meningiomas are common, typically benign intracranial neoplasms with well-demarcated borders.Meningiomas with indistinct boundaries have been reported.These can invade surrounding structures, and present surgical and diagnostic challenges. We present the case of an unusual meningioma in a 53-year-old male in which preoperative magnetic resonance imaging (MRI) revealed an irregular lesion with clear boundaries and peripheral rim enhancement. Intraoperatively, however, no cleavage plane was apparent. Histological examination showed an increase of fibroconnective tissue with proliferation of dilated vessels in the periphery of the tumor concordant with the rim.Immunohistochemical staining of the tumor was positive for EMA and CD34, but negative for CEA, Ki67, and GFAP. Immunohistochemical staining of proliferating vessels in the periphery of the tumor was positive for CD34. A so-called ‘capsule’ structure was suggested according to MRI findings and pathological examination.The tumor was diagnosed as a mixed type meningioma,WHO grade I.