Glioneuronal tumor with neuropil-like islands (GTNI)
GTNI is a rare neoplasm of neuronal differentiation and diffusely infiltrating astroglial and oligodendrocyte-like components showed characteristic histologic features and immunoprofile arising in adults, which was included in the 2007 World Health Organization (WHO) classification of central nervous system tumors as a pattern variation of anaplastic astrocytoma (5). Later, it had been added to the group of glioneuronal tumors in the most recent update of the World Health Organization classification of tumors of the central nervous system (1).
Teo et al (8) described firstly a four-case series with GTNI in 1999. Since then, it has been reported to occur in the adult cerebrum mainly. Whereas spinal GTNI localization is relatively rare (4,6,7). The tumor contained predominating micronodular neuropil-like islands and the diffusely infiltrating glial component. The latter, consist mainly of GFAP-positive, fibrillary and gemistocytic elements identical to those populating conventional astrocytomas, but can include small numbers of GFAP negative cells resembling oligodendrocytes. GTNIs seem to behave in a manner comparable to neoplasms of diffuse astrocytic type when matched for WHO grade of their glial components. Even though they can exhibit low-grade morphology and low cell proliferation indices, most cases in the literature have shown progression, so this lesion should be considered as aggressive (2). The microvascular proliferation changes of this case resembling high-grade gliomas implied its anaplastic temperament (5).
The main differential diagnoses include oligodendroglioma and extraventricular neurocytoma. Some oligodendrogliomas may contain neoplastic cells that express synaptophysin and/or other neuronal markers, such as NeuN, NF and others, but they lack neuropil-like islands immunoreactivity for synaptophysin. Characteristic 1p and 19q deletions, seen in almost 50% to 80% of the cases of oligodendrogliomas, are not observed in glioneuronal tumors with neuropil-like islands. Extraventricular neurocytoma differs from GTNI by its diffuse immunoreactivity to synaptophysin in fibrillary zones and perivascular nuclei-free cuffs. Importantly, a significant number of nuclei are immunopositive for NeuN in almost all cases.
From above, it seems that GTNI does not share pathologic or genetic features with conventional astrocytoma, suggesting a unique entity with aggressive behavior. Moreover due to the rarity of this pattern, the prognostic significance of the GTNI is yet to be ascertained and the potential molecular differences accounting for GTNI still remains to be identified. Chemotherapy and stereotactic radiosurgery have also been advocated. However, the value of these treatment modalities on disease progression in GTNI will need to be further investigated in prospective study.
Contributed by Cui-Yun Sun, PhD; Shi-Zhu Yu, PhD; Qian Wang, PhD; Tong-Ling An, MD; Yan-Jun Wen, MD