Glial fibrillary acidic protein immunopositive neuroglial tissues with or without ependyma-lined canal in spinal lipoma of filar type: Relationship with retained medullary cord.

Background: Retained medullary cord (RMC) and filar lipomas are believed to originate from secondary neurulation failure; filar lipomas are reported to histopathologically contain a central canal-like ependyma-lined lumen with surrounding neuroglial tissue with ependyma-lined central canal (NGT w/E-LC) as a remnant of the medullary cord, which is a characteristic histopathology of RMC. With the addition of glial fibrillary acidic protein (GFAP) immunostaining, we reported the presence of GFAP-positive NGT without E-LCs (NGT w/o E-LCs) in RMC and filar lipomas, and we believe that both have the same embryopathological significance.

Methods: We examined the frequency of GFAP-positive NGT, with or without E-LC, in 91 patients with filar lipoma.

Results: Eight patients (8.8%) had NGT w/E-LC, 25 patients (27.5%) had NGT w/o E-LC, and 18 patients (19.8%) had tiny NGT w/o E-LC that could only be identified by GFAP immunostaining. Combining these subgroups, 56% of the patients (n = 51) with filar lipoma had GFAP immunopositive NGT.

Conclusion: The fact that more than half of filar lipomas have NGT provides further evidence that filar lipoma and RMC can be considered consequences of a continuum of regression failure that occurs during late secondary neurulation.