Syrinx morphology in Chiari II malformations. A Type 1 syrinx: the ventral portion of the cavity is ependymal lined (asterix), while the dorsal aspect is irregularly lined by a layer of hyperplastic glia (arrow). Despite the lack of dorsal ependymal lining, the impression that this is simply a wedge shaped extension of the more caudal dysraphism is difficult to escape. B Type 2 syrinx, extending in this section into the cervical cord, with a prominent paramedian and dorsal distribution. The arrow indicates the normal dorsal and median glial raphe and arrowheads the slit-like paramedian syrinx. This cavity was continuous with the dilated central canal (asterix) caudally. C Dorsal aspect of the same section as B at higher power, demonstrating glial processes lining a slit like cavity containing macrophages, with axonal tracts in the walls of the cavity. D and E: Same specimen, type 3 syrinx, demonstrating irregular extension of the syrinx both dorsolaterally (D) and ventrolaterally (E). The cavity marked by an asterix is partially lined by ependyma and is continuous with the central canal. All sections stained immunohistochemically for vimentin.Fetal syringomyelia. Guo A, Chitayat D, Blaser S, Keating S, Shannon P - Acta neuropathologica communications (2014). Not Altered. CC.