Brain tumour. Magnetic resonance imaging (MRI) scan of an axial section through the brain of a 54-year-old male patient, showing the presence of a large ganglioglioma tumour (dark, round, upper left) affecting the frontal lobe of the right hemisphere. Ganglioglioma is a rare, slow-growing tumour that affects the central nervous system (CNS), most often in the temporal lobes of the brain. They are usually benign (non-cancerous). Here, there is also peripheral oedema (fluid accumulation) and a mass affecting the lateral ventricles.