Can an mri tell if a brain tumor is benign or malignant?

Maybe, or not: Sometimes appearance is characteristic, sometimes not. Other imaging, including pet/ct can help differentiate.

Sometimes.: Depending on the imaging characteristics of the brain abnormality, MRI may be able to tell if it's benign or malignant. A meningioma (benign) has a characteristic appearance and can be diagnosed on mri. Certain malignancies are also characteristic. Contrast enhancement & spectroscopy on MRI are useful.