Mixed oligodendroglioma ependymoma is a rare and complex type of brain tumor that originates from the cells that make up the central nervous system. This tumor consists of a mixture of two specific types of brain tumors: oligodendroglioma and ependymoma. The term "mixed" refers to the presence of both these tumor types within a single tumor. Oligodendroglioma is a slow-growing tumor that arises from the cells that produce a protective covering called myelin in the brain, while ependymoma originates from the ependymal cells that line the ventricles in the brain and the central canal of the spinal cord.