Dynamic MRI of meningiomas and schwannomas: is differential diagnosis possible?

We studied 23 patients with meningiomas and 14 with schwannomas using dynamic spin-echo (TR/TE 200/15 ms) MRI. Histologically the meningiomas were classified according to the 1993 WHO classification. Serial images were obtained every 30s for 210s after rapid injection of gadopentetate dimeglumine (0.1 mmol/kg). The contrast-enhancement ratio (CER) was divided into three patterns; a sharp rise with a peak within 60 s (A), a relatively rapid increase with a peak between 60 and 210s (B), a slow increase without a peak (C). The patterns were correlated with the histology of the tumors. The signal intensities of the tumours on T2-weighted images were also analyzed and correlated with the dynamic patterns. Meningiomas had more varied dynamic patterns than schwannomas. Almost half of the meningiomas showed pattern A, and one third pattern C. Of six meningiothelial meningiomas showed pattern A; all schwannomas and fibrous meningiomas showed pattern C. Various patterns were observed in transitional meningiomas. Of the 8 meningiomas showing pattern C, only one gave high signal on T2-weighted images, and could not be differentiated from the schwannomas. Thus, one third of meningiomas could not be differentiated from schwannomas by the dynamic contrast enhancement alone. However, when this was combined with the signal intensity on T2-weighted images, most meningiomas could be differentiated from schwannomas.