Objective: Although tumors are generally expected to grow exponentially, it is not known whether meningiomas retain a constant growth rate or not because of the lack of long-term follow-up. We analyzed the long-term growth pattern of meningiomas.
Methods: Twenty patients with a total of 31 meningiomas were radiologically followed for 4.1 to 18.3 years (median, 10.1 yr). Seven patients (including two neurofibromatosis cases) had incidental tumors. Another 13 patients with symptomatic tumors were followed after surgery. Their volumes were measured, and their time-volume curves were plotted.
Results: The growth curves of four atypical meningiomas fitted better to an exponential curve (R > 0.95). Two calcified tumors did not grow. Although the other benign tumors grew exponentially or linearly, their tumor volume doubling times in the initial phase were shorter than those in the later phase in most cases. Meningiomas without calcification tended to grow exponentially, whereas those with calcification were likely to reveal a linear growth pattern (P = 0.002, chi2 test). This was supported by the observation that in two patients, the tumor growth pattern changed from exponential to linear and from linear to no growth with progression of calcification.
Conclusion: Three growth patterns of meningiomas were demonstrated. Atypical meningiomas grew exponentially. Conversely, benign meningiomas revealed exponential, linear, or no growth. The growth pattern of the latter may change with the appearance of calcification.