This patient went on to have a biopsy which revealed the lesion to be a pineocytoma. The report of the histology is no longer available and predates 2010. Given the ill-defined margins, high signal on DWI suggesting probably reduce ADC values and edema in the surrounding parenchyma the imaging appearances are more in keeping with a higher grade tumor such as a pineal parenchymal tumor with intermediate differentiation (WHO II or WHO III) or even pineoblastoma (WHO IV). 

Given that this tumor likely was assessed histologically prior to pineal parenchymal tumors with intermediate differentiation being included in the WHO classification of CNS tumors it is probable that were it to be assessed now it would prove to be a WHO grade III tumor. 

We will never be able to tell, but it remains a good teaching case.