Although some authors have reported the malignant transformation of meningiomas, there has been no previous report describing that a meningothelial meningioma transformed into an atypical meningioma within 1 year. This report documents a 57-year-old woman who presented with right hearing disturbance. Magnetic resonance imaging revealed a right petroclival meningioma. The tumor was subtotally removed and was diagnosed to be a meningothelial meningioma. Seven months after surgery, a recurrence of the tumor was confirmed. The diagnosis of this recurrent tumor was an atypical meningioma. The MIB-1 index and the percent of p53 protein-positive cells in the primary tumor were 4.6% and 35.4%, respectively, whereas those of the recurrent tumor were 34.7% and 33.1%, respectively. A chromosomal DNA copy number loss was observed on 1p, 6q, 10, 14q, and -22q detected in both the primary and the recurrent tumors. These results suggest that the present case had a potentially malignant tumor in the early stage, although it had the histological features of benign meningiomas. An evaluation of the MIB-1 index, as well as the expression of p53 and chromosomal aberrations, may be useful for predicting the malignant transformation of meningiomas.
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