Objective. Intracranial meningiomas are mostly considered to be slow growing tumors. However, only a few previous reports provide information on the growth rate of these tumors. The aim of this study was to determine the growth rates of intracranial meningiomas after subtotal resection, analysing their relation to radiological appearance and histological features. Results are compared with our previous analysis of growth rates in incidental meningiomas.

Methods. The hospital charts, follow up records and imaging studies were reviewed in 36 patients with subtotally resected intracranial meningiomas. The tumor growth rates were determined by calculating the absolute and relative growth rates and the tumor volume doubling times.

Results. In the group of 33 patients with histologically verified grade 1 meningiomas, the mean absolute growth rate was 1.51 cm³/year, the median relative growth rate and tumor doubling time was 14.18%/year and 5.228 years. In young patients annual relative growth rates were significantly higher. The median annual relative growth rate of meningiomas with calcification was significantly lower than in tumors without calcification. Also tumors with hypo— or isointense T₂-signals on MRI revealed a lower growth rate. There was no significant difference between males and females. Histological studies revealed 22 meningiomas of a meningotheliomatous subtype, 8 fibrous and 3 psammomatous meningiomas. The comparison of growth rates between these subtypes did not show any significant differences. In atypical meningiomas (WHO grade 2), absolute and relative growth rates were significantly higher and tumor doubling times shorter.

Conclusion. The majority of intracranial meningiomas are slow growing tumors, although the growth rates may vary widely even among benign grade 1 meningiomas. In meningiomas after subtotal surgical resection, the age of the patients seems to present a predictive factor for tumor growth in analogy to our previous observation in incidental meningiomas. Significantly higher relative growth rates were detected in younger patients. Gender does not seem to play a major role as a predictive factor. Radiological features such as calcification or T₂-signal intensity may provide additional information to predict the growth potential of meningiomas. Close clinical and radiological observation should be performed in young patients harboring tumors with absence of calcification or high T₂-signal intensities due to the higher growth potential in this patient group.