A 30-year-old patient presents with headache and is found to have a mass located in the anterior right lateral ventricle on brain MRI. The mass appears to be well-defined, solid and cystic, and shows heterogenous contrast enhancement. A biopsy is performed, with H&E photomicrographs and immunostains shown. Tumor cells are additionally found to be non-reactive for an Olig2 immunostain. 

What is your diagnosis?

A. Oligodendroglioma, CNS WHO grade 2

B. Ependymoma, CNS WHO Grade 2

C. Ganglioglioma, CNS WHO Grade 1

D. Central neurocytoma, CNS WHO Grade 2