Prospective study on patients with orbital tumors of unknown origin. Aim of the study is to differentiate benign from malignant tumors upon MR imaging. Magnetic resonance imaging of the orbit will be performed including standard morphological sequences and advanced sequence techniques. These advanced sequence techniques may allow to differentiate benign from malignant tumors based on their cellularity and vascularity (diffusion and perfusion imaging). These MRI data will be analysed and the level of diffusion and perfusion will be measured and compared to the histological findings. Cut-off values of diffusion and perfusion will be calculated that allow to separate benign from malignant tumors.