Tectal glioma: clinical, radiological, and pathological features, and the importance of molecular analysis

Abstract

Tectal glioma (TG) is a rare lower grade glioma (LrGG) that occurs in the tectum, mainly affecting children. TG shares pathological similarities with pilocytic astrocytoma (PA), but recent genetic analyses have revealed distinct features, such as alterations in KRAS and BRAF. We conducted a retrospective review of cases clinically diagnosed as TG and treated at our institute between January 2005 and March 2023. Six cases were identified and the median age was 30.5 years. Four patients underwent biopsy and two patients underwent tumor resection. Histological diagnoses included three cases of PA, one case of astrocytoma, and two cases of high-grade glioma. The integrated diagnosis, according to the fifth edition of the World Health Organization Classification of Tumours of the central nervous system, included two cases of PA and one case each of diffuse high-grade glioma; diffuse midline glioma H3 K27-altered; glioblastoma; and circumscribed astrocytic glioma. Among the three patients who underwent molecular evaluation, two had KRAS mutation and one had H3-3A K27M mutation. Our results demonstrate the diverse histological and molecular characteristics of TG distinct from other LrGGs. Given the heterogeneous pathological background and the risk of pathological progression in TG, we emphasize the importance of comprehensive diagnosis, including molecular evaluation.

Keywords: KRAS; H3 K27M; Lower grade glioma; Molecular analysis; Tectal glioma.

Fig. 1

Progression-free survival and overall survival in our cohort. The median progression-free survival (PFS) was 3.4 years (A). The median overall survival (OS) was 6.2 years (B)

Fig. 2

Radiological, histological findings and DNA methylation analysis in Case 2 (A–G). The tumor was located in the tectum and exhibited high intensity on FLAIR (Fluid Attenuated Inversion Recovery) images (A) and partial enhancement after gadolinium administration (B, C). Hematoxylin and eosin staining revealed microvascular proliferation (D), mitosis (with the arrow indicating a mitotic cell), and proliferation of atypical tumor cells with irregular nuclei (E). The Ki-67 proliferation index was 5.7% in the most stained areas (F). The scale bar indicates 200 μm (D, F) and 50 μm (E). Genome-wide DNA methylation showed no KIAA1549::BRAF fusion (G)

Fig. 3

Radiological, histological findings and DNA methylation analysis in Case 3 (A–F). The ventricles were enlarged, the tumor was located in the tectum and exhibited high intensity on FLAIR images (A). Tumor was not enhanced after gadolinium administration (B, C). Hematoxylin and eosin staining revealed a biphasic pattern with alternating dense and loose components (D). Glial cells with long, hair-like (piloid) processes were observed, and Rosenthal fibers appeared as brightly eosinophilic structures (D). Tumor cells were positive for the H3K27M antibody (E) and negative for the H3K27me3 antibody (F) in immunohistochemistry. The scale bar indicates 200 μm (D) and 50 μm (E, F). The copy-number profile of the genome-wide DNA methylation is shown (G)