What is the favoured diagnosis?
The appearance is strongly in favour of a high grade primary glial tumour (glioblastoma (GBM) WHO Grade IV).
What is the differential for this lesion?
The main differential of a lesion crossing the corpus callosum is primary CNS lymphoma. Provided the patient has not received steroids and is not immunocompromised (e.g. HIV AIDS) the heterogeneous and peripheral enhancement would be unusual for lymphoma.
MRI better characterises the lesion, and shows it to be of low signal intensity on T1 weighted sequences and heterogeneous intensity on T2 weighted images with ares of high signal centrally (necrosis).
Contrast enhancement is prominent but heterogeneous and predominantly peripheral. The solid components demonstrate restricted diffusion, suggesting high cellularity.