Atypical and malignant meningiomas: importance of micronecrosis as a prognostic indicator.

Twenty-eight patients with a diagnosis of either atypical or malignant meningioma, according to the World Health Organisation (WHO) classification, were followed up to relate histopathological features with times to recurrence and death. Five year disease-free survival was 41% with a median disease free survival of 27 months. Micronecrosis was the only histopathological feature associated with increased risk of recurrence (rate ratio, 3.73: 95% confidence interval 1.03-13.6). At 36 months, 32% of patients with micronecrosis were alive compared with 71% of patients without micronecrosis. Brain invasion was not associated with disease-free survival. After recurrence, median survival was 7 months and was not correlated with any histopathological feature. The prevalence of micronecrosis was estimated from random samples of benign, atypical and malignant meningiomas to be 8%, 42% and 71% respectively. The relevance of these findings and the current WHO classification is discussed.