[Pathological anatomy of tumors of the third ventricle]

The walls of the third ventricle contain a large variety of tissues, and the pathological processes in this area are extremely varied. The pathological lesions encountered in the third ventricle are analyzed with interest to their incidence in the national series. Colloid cysts have a single layer of epithelial cells, mimicking the bronchus epithelium, which may reveal their probable endodermic origin. Xanthogranulomas are not true neoplasms but are only reactional to local hemorrhages. Histological diagnosis may be difficult for glial tumors if the biopsy sampling is insufficient : pilocytic astrocytomas can be overgraded and confused with high grade astrocytomas. Subependymomas should be separated from ependymomas, and giant cell subependymal astrocytomas are specific lesions occurring in tuberous sclerosis. Craniopharyngiomas often show a papillary type when located in the third ventricle. Germinal tumors are associated with immunological markers. The variety of the encountered lesions in the third ventricle needs a close collaboration between neuropathologists and neurosurgeons, and a confrontation of histological data with clinical and radiological data.