Discrepancy between computed tomography and magnetic resonance imaging in a case of medulloblastoma

In a 2-year-old girl with signs and symptoms of a posterior fossa tumor, the computed tomographic scan showed what appeared to be a brain stem glioma. However, magnetic resonance imaging (MRI) demonstrated the lesion to be extrinsic to the brain stem. Posterior fossa exploration disclosed a medulloblastoma filling the 4th ventricle. This discrepancy in imaging techniques points out the usefulness of MRI in the evaluation and treatment of posterior fossa lesions.