Glioneuronal
tumor with neuropil-like islands (GTNI) is featured by "neuropil-like islands (NIs)" within dominating astroglial components.
Isocitrate dehydrogenase (IDH) mutations, particularly IDH1 R132H (G395A), are found in WHO Grade II and III diffuse
gliomas as well as secondary, but not primary,
glioblastomas. We reviewed 5 cases of GTNI, and assessed histology and immunohistochemistry with various
antibodies, including those for IDH1 R132H, as well as direct
DNA sequencing for IDH1 G395A. NIs were variable in morphology, and constantly
synaptophysin-positive and
glial fibrillary acidic protein-negative. The
glioma components were primary
glioblastoma in 2 cases,
anaplastic astrocytoma in 1 and anaplastic oligoastrocytoma in 2. The IDH1 R132H was expressed in the 2 cases with oligoastrocytoma: In 1, NIs and the
astrocytoma-like area as well as the
oligodendroglioma-like area were positive. In the other, only the oligodendrogliomalike area was positive. The mutation analysis performed on the latter case with
DNA separately sampled from the
oligodendroglioma- like area and the
astrocytoma-like area detected IDH1 G395A in both areas. We have shown diverse pathologic aspects of GTNI. Also, we have shown that the expression of IDH1 R132H in GTNI is largely concordant with that in diffuse
gliomas, and that it can be dependent on each histologic component although the mutant IDH1 gene is ubiquitously present within the
tumor.