Ependymoma: Ependymomas usually arise from the ependyma lining of one of the ventricles. This specimen is a transverse section through a poorly differentiated and rapidly growing ependymoma that has completely filled and distended the fourth ventricle. It has displaced and focally infiltrated the cerebellum. As with astrocytomas, the margin of ependymomas may be sharply demarcated, or may be indistinct. Signs and symptoms related to obstruction of the fourth ventricle occur as well as disturbance of cerebellar and brain stem function.