Extraventricular neurocytoma (EVN), a variant of central neurocytoma, is a rare neuronal neoplasm, composed of round cells with neuronal differentiation, which is located outside of the ventricular system, usually within the spinal cord or cerebral hemispheres and that manifests with headache, nausea, vomiting, complex partial seizures or focal neurological deficits. In some cases it may exhibit atypical features consistent with aggressive clinical behavior. The disease is extraventricular neurocytoma (Monarch Disease Ontology id MONDO_0016727). Also known as: EVN, extraventricular neurocytoma (WHO grade II).