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located on chromosome 22 has been suggested. Aberrations involving chromosomes 1, 6, 7, 9, 10, 11, 12, 13, 16, 17, 19 and 20 have been reported less frequently. Ependymomas are genetically different from astrocytic and oligodendroglial tumours. No mutations or deletions of the tumour suppres- sor genes CDKN2A and CDKN2B and no amplification of CDK4 or CCND1 or EGFR have been described [23,24] . The p53 gene has only a minor and unclear role in induction of ependymomas [25,26] . However, mdm2 gene amplification has been found in up to 35% of ependymomas [27] . The gene product MDM2 is believed to act as a cellular regulator of p53-mediated tumour growth. MDM2 immunopositivity was detected in 96% of specimens, suggesting not only a role of mdm2 amplification in the tumorigenesis of ependymoma but also the presence of a mechanism of MDM2 overexpression other than gene amplification [27] . Analyses of mutations of the NF2 suppressor gene yielded conflicting results [28,29] . It is likely that NF2 mutations are related to spinal ependymo- mas only [30] , which constitute a molecular variant, while a tumour-suppressor gene, independent of the NF2 gene, might be implicated in the genesis of cerebral ependymomas [31] . The cytogenetic aberrations seem to differ between tumours from adult and younger patients, and between intracranial and spinal ependymomas [32] . Clinical presentation is non-specific, and depends on the size, location and malignancy of the tumour. Anaplastic ependymomas give rise to signs and symptoms more rapidly. Intraventricular ependymomas often cause headache, nau- sea and vomiting, papilloedema, ataxia, and vertigo due to increased intracranial pressure and hydrocephalus. The compression of posterior fossa structures leads to visual dis- turbances, ataxia and hemiparesis, dizziness and neck pain. Patients with extraventricular supratentorial ependymomas may show forgetfulness, behavioural changes and lethargy with signs like seizures and focal neurological deficits. Spinal cord lesions are typically associated with back pain of long duration, and motor or sensory deficits of lower and upper extremities. Ependymomas are more commonly infratentorial (60%), particularly in the fourth ventricle, and in 50% of cases can extend into the subarachnoid space of the cisterna magna or the cerebello-pontine angle, or involve the medulla and upper cervical cord [33,34] . The second most common loca- tion is the spinal cord, followed by the lateral ventricles and the third ventricle. Approximately one-half of supratentorial ependymomas are parenchymal and one-half are primarily intraventricular, arisingmore often (75%) in the lateral ventri- 3. Diagnosis 3.1. Clinical presentation 3.2. Localisation

in the conus-cauda-filum terminale region) and subependy- moma, a benign, slowly growing intraventricular lesion with a very favourable prognosis, WHO grade II ependymoma andWHO grade III anaplastic ependymoma. Ependymoblas- tomas are being classified as primitive neuroectodermal tumours (PNET) and must be distinguished from anaplastic ependymomas. 2.1.1. Myxopapillary ependymoma (WHO grade I) This entity is characterised by cuboidal tumour cells, with GFAP expression and lack of cytokeratin expression, sur- rounding blood vessels in a mucoid matrix. Mitotic activity is very low or absent. 2.1.2. Subependymoma (WHO grade I) Subependymoma has isomorphic nuclei in an abundant and dense fibrillary matrix with frequent microcysts; mitoses are very rare or absent. 2.1.3. Ependymoma (WHO grade II) This neoplasm has moderate cellularity; mitoses are rare or absent and nuclear morphology is monomorphic. Key histological features are perivascular pseudorosettes and ependymal rosettes [14] . Four histological variants have been described: cellular ependymoma, which has hypercellularity and increased mitotic rate, papillary ependymoma, clear cell ependymoma and tanycytic ependymoma. 2.1.4. Anaplastic ependymoma (WHO grade III) This tumour is characterised by hypercellularity, cellular and nuclear pleomorphism, frequent mitosis, pseudopalisad- ing necrosis and endothelial proliferation. The latter two criteria do not appear to be independently related to prognosis [15] . Perivascular rosettes are a histological hallmark. 2.2.1. Immunophenotype Ependymomas typically express GFAP, particularly in pseudorosettes and in grades I–II lesions, S100 protein and vimentin [16,17] . In some cases, focal expression of cytok- eratins has been observed [18] , while neuronal antigens are never observed. The proliferation index is variable and is higher when anaplastic features are present or the patient is aged 2.3.1. Genetic features Data concerning the cytogenetic features of ependymoma are sparse. Approximately two thirds of patients exhibit cyto- genetic abnormalities but no primary deletion is evident. The most frequent abnormal cytogenetic features consist of monosomy 22 or in various translocations involving chromo- some 22, which have been detected in approximately 30% of cases [19–22] . The absence of a tumour-suppressor gene 2.2. Immunophenotype 2.3. Genetic features