A 52 year-old male is admitted with sudden onset of weakness affecting the left arm. He has a background of grade III astrocytoma of the right parietal lobe which was resected. This was followed by radiotherapy which was completed around 12 months ago. Over the last 2 weeks, he has been getting daily throbbing headaches lasting around 2 hours and associated with nausea and photophobia. On examination, he has power 0/5 in all muscle groups of the left arm. Two days after hospital admission, he has 4 episodes of twitching over the left side of the face which progress to generalised tonic-clonic seizures. He is started on a loading dose of phenytoin with good effect. MRI FLAIR, T1 post-contrast and DWI do not show any acute abnormality compared to previous scans. However, the weakness persists and on day 7 of admission a repeat MRI is performed. FLAIR, T1 post-contrast and DWI sequences are shown below. What is the most likely diagnosis?