These patients presented with an unusual myxoid lesion similar to the pilocytic astrocytoma but with other features of the myxopapillary ependymoma. On gross histology, the tumor was grossly heterogenous with firm tan areas interrupted by multiple foci of softened reddish tissue and central necrosis. On light microscopy, all surgical specimens were composed of a monotonous population of cells with delicate piloid-like processes, loosely arranged within a prominent myxoid background. Focally, the neoplastic cells converged upon small blood vessels in pseudorosette-like formations. There was minimal nuclear pleomorphism and mitotic figures (Figure 6B). These histomorphologic features are identical to those of the recently described astrocytoma with monomorphous pilomyxoid features (1). The tumor cells showed strong cytoplasmic immunoreactivity with antibodies to glial fibrillary acidic protein (GFAP) and vimentin, as well as nuclear and cytoplasmic staining with S-100 (Figure 6C). All cases stained positive for synaptophysin and negative for chromogranin (Figure 6D). This is in contrast to astrocytomas, which do not stain positive for synaptophysin. Electron microscopy (EM) in four of the cases revealed the presence of neoplastic cell bodies in the third ventricle ependymal lining with long synaptic processes extending to adjacent blood vessels and apical surfaces displaying microvilli, cytoplasmic blebs and rare cilia. Neuronal tumors have true synaptic junctions while this neoplasm displayed synaptoid complexes in closely apposed processes containing vesicles (Figure 6E). The neoplastic cells in all cases were identical in both staining and EM characteristics of the normal tanycyte (Figure 6A)(2,4).

A.		B.
C.		D.
E.

Figure 6. Pathology of tanycytomas

1. H & E histology: stained normal tanycytes radiating to blood vessel in area postrema.
2. H & E histology: stained tanycytes radiating to blood vessel in tanycytoma specimen.
3. Immunoreactivity to glial fibrillary acidic protein (GFAP): positive brown stained glial processes radiating to blood vessel in tanycytoma specimen.
4. Immunoreactivity to synaptophysin: positive brown stained glial processes radiating to blood vessel in tanyctoma specimen.
5. Electron microscopy: tanycytes with long synaptic processes (red arrow) and synaptic junctions (yellow arrow) from a tanycytoma specimen.