[A case of recurrent convexity meningioma with malignant transformation 26 years after total tumor removal].

Meningiomas are common intracranial tumors, the majority of which are considered benign. However, they sometimes show altered biologic behavior, associated with local aggressiveness and late distant metastasis. We report a patient with a convexity meningioma, which recurred as a malignant transformation 26 years after a total tumor removal. A 75-year-old man was transferred to a local hospital because of general convulsions and left hemiparesis. The patient had had an operation for the total removal of a right frontal convexity meningioma at the age of 46 and had been free of its effects until the age of 72. Brain magnetic resonance imaging (MRI) showed a recurrent tumor located in the anterior area of the previous craniotomy. Over the following two and a half years, MRI revealed rapid enlargement and infiltration of the tumor into the brain parenchyma. The primary tumor was nodular, macroscopically well demarcated from the surrounding brain tissue and, histologically, was a transitional type of meningioma without any atypical features. In contrast, the recurrent tumor, whose border was ill-defined, had invaded the neighboring brain. A histological specimen of the recurrent tumor showed highly malignant features such as necrosis, intracerebral infiltration, dense cellularity, and high proliferating activity as demonstrated by a cell kinetic study using the MIB 1 staining index. We should be mindful that recurrence from common benign type meningiomas may occur as malignant transformations after more than two decades.