Infratentorial ependymoma in the fourth ventricle CMRI axial T1 with contrast mediumCMRI sagittal T1 with contrast mediumCMRI coronal T1 with contrast medium Ependymomas are tumors of the central nervous system with different biological behavior (classification in grade 1 to 3 according to WHO). Often they are slow-growing with a relatively favorable prognosis. They have their origin in the ependyma, the epithelial lining of the ventricles and central canal of the spinal cord. Thus they always have a topographical relation to the ventricular system or lie directly subependymal. This also explains the most common symptoms: Occlusion hydrocephalus with intracranial ependymomas or local pressure on nerve fibers in the spinal canal in the area of the medullary conus and cauda equina. Intracranially they occur frequently in childhood and adolescence and are among the most common intracranial tumors in infancy. Despite the slow growth and the overall often favorable prognosis, there are often, even after many years, relapses, especially after incomplete surgical removal. If a patient had an ependymoma once, he should get checked for recurrences regularly for his whole life. The prognosis for patients is mainly determined by the location and extent of the tumor, determined histological classification (grade 1 to 3 according to WHO), surgical treatment options (radical), and primary symptoms. It is easy to understand that large tumors of the cauda equina are rarely removed completely and can even before surgery lead to paraplegia that can often not be cured. Another unique feature of ependymomas is their tendency to intrathecal metastasis, which also influences prognosis.