Leptomeningeal metastases. When assessing an MRI brain for metastatic disease, in addition to searching for focal lesions in the cerebrum and cerebellum, we have to look carefully at the post-contrast sequences for abnormal enhancement of the meninges due to metastatic infiltration. This can be very subtle, as in this example. The image on the left is non-contrast T1-weighted, and appears normal, however following gadolinium injection, the T1-weighted image on the right shows abnormal enhancement of the meninges around the midbrain and along the cerebellar folia (arrows). This patient had a background of lung cancer, which is one of the most common sources of meningeal metastatic disease, in addition to breast cancer and melanoma.