These hypothalamic-suprasellar and ventricular tumors had an unusual histomorphology with a mixture of ependymal and piloid-like astrocytic features and a myxoid stroma. Pilocytic astrocytomas and myxopapillary ependymonas (MPE) need to be considered in the differential diagnosis. Less than 8% of all intracranial ependymonas occur in the third ventricle location (5). There have been only three reported cases of intracranial myxopapillary ependymonas with none involving the third ventricle (6). This new tumor lacks the typical hyalinized vessels and papillae of MPE. The hypothalamic and chiasmatic region is a classic location for pilocytic astrocytomas. In contrast to the pilocytic astrocytomas, this new tumor lacks rosenthal fibers, eosinophilic granular bodies and alternating solid and loose areas. On the electron microscopy, these tumor cells have more epithelial-type features that are not seen in astrocytomas. These tumor cells have similar microscopic features of the tanycyte. Tanycytes were first described by Horstmann in 1954 and are found in the floor of the 4th ventricle, aqueduct of Sylvius, circumventricular organs and most commonly in the infralateral walls of the floor of the third ventricle (4,7). The tumor cells of our cases shared several common ultrastructural features with tanycyte such as microvilli and apical blebs, coated pits, vesicles, intercellular junctions and singular elongated processes with well-formed end feet. Other very rare gliomas, the astroblastoma (8) and subependymomas (9) have had suggested origins from tayncytes. We propose the name "tanycytoma" to describe this new tumor.

Conclusion

The tanycytoma is a distinct histologic entity now recognized in the pathology literature. The imaging characteristics may not allow for clear differentiation from gliomas but histologic and electron microscopic examination can conclusively diagnose this tumor. Increased awareness of this neoplasm is necessary so that we may learn more about the diagnosis, treatment and prognosis of the tanycytoma.