[Lipomatous ependymomas of the posterior fossa. An infrequent and little-known subtype. A case report and review of the literature].

Ependymomas are well defined glial tumours composed of uniform small cells with round nuclei in a fibrillar matrix. They have characteristic perivascular acellular areas (pseudorosettes) and, in some cases, ependymal rosettes. The three most well-known histological phenotypes are papillary, clear-cell and tanycytic. The WHO classification includes rare cases of ependymoma with lipomatous metaplasia. Lipomatous ependymomas of the posterior fossa are extremely rare; we only found 7reports of cases in adults. They usually arise in the fourth ventricle and may extend into the cerebellum, when they often show extensive vacuolization, pushing the nucleus to the periphery and giving rise to a signet-ring cell appearance. Radiologically, there are few findings characteristic of these tumours. Immunohistochemistry is essential to differentiate this subtype from other more common lesions, such as metastatic adenocarcinoma, especially from breast, intestine and kidney.