Diffuse Leptomeningeal Glioneuronal Tumors: A Case Series of Five Patients with Parenchymal Forms and an Analysis of the Diagnostic Challenges, Treatment Options and Outcomes.

Background: Diffuse leptomeningeal glioneuronal tumors (DL-GNT) are rare glioneuronal neoplasms with oligodendroglioma-like cells. These tumors can present as a dominant intracranial mass or as a solitary spinal cord mass without leptomeningeal involvement. In this study, we aimed to determine the magnetic resonance imaging and histopathological features, treatment modalities, and clinical outcomes of the parenchymal forms of DL-GNTs.

Methods: This is a retrospective three-center case series study of 5 patients with a confirmed parenchymal form of DLGTs, out of which 4 patients were adults. Brain and spinal cord MR imaging were performed in all patients at either 1.5 or 3T. The patients' age ranged from 5 years to 50 years with a mean age of 27.6 years at presentation.

Results: Four of the tumors were located in the frontal lobe, and one in the tectum. They were usually solid-cystic enhancing tumors as the other mixed neuronal-glial tumors. All of the tumors had an extension to the superficial surface of a cerebral hemisphere. One had systemic bone metastases. The clinical signs and symptoms of the parenchymal form varied based on the location of the mass, in contrast to the leptomeningeal form associated with hydrocephalus. In one case, the tumor's initial grade was defined as intermediate. The initial histopathology of the two cases was low-grade and no upgrade occurred in the follow-up period. In two cases, although the tumors were low grade initially, they progressed to an anaplastic form in the follow-up period.

Conclusion: The parenchymal form of DL-GNTs is common in adults. Extension to the superficial surface of a cerebral hemisphere is a distinctive imaging feature. Systemic osseous metastasis may occur. Due to the presence of common histopathological features, including the biphasic composition of glial and neuronal cell elements and oligodendroglioma-like cells, a proposed classification approach might be more beneficial for the histopathological and imaging description, and management of the glioneuronal tumors with oligodendroglioma-like features.