Background/Objectives: Diffuse midline glioma (DMG), H3 K27M-altered, represents a rare group of gliomas arising in midline structures of the central nervous system. Historically regarded as a pediatric entity, it is now increasingly recognized in adults. Although its relative prevalence among all midline diffuse gliomas and its clinical-radiological characteristics are well defined in children, these tumors remain less characterized in adults, and comparative evaluations with H3 K27 wildtype midline diffuse gliomas are limited. Methods: Consecutive adult patients with histopathologically confirmed diffuse glioma (WHO grade ≥ 2) diagnosed between 2016 and 2025 were retrospectively screened for midline tumor location, with systematic revision of imaging and pathology. For identified midline diffuse gliomas, comprehensive clinical, imaging, and immunohistochemical data were collected, and a detailed morphometric analysis was performed. H3 K27 alteration status was established immunohistochemically, with supplementary immunostaining when necessary. Descriptive and comparative analyses were conducted. Results: A total of 5% of the 541 adult diffuse gliomas were midline, and 23% of IDH wildtype midline gliomas were consistent with DMG, H3 K27-altered (all H3 K27M-mutant). The affected patients were significantly younger, and these tumors predominantly involved the thalamus and mesencephalon. Morphometric analyses revealed trends toward fewer high-grade features in H3 K27-altered tumors, with composite scores demonstrating significant discriminatory ability. The overall survival was not significantly different between groups but showed associations with ring-like enhancement as well as adjuvant and salvage therapies in the overall midline cohort. Conclusions: This study provides population-based prevalence estimates for DMG, H3 K27M-altered, and complements the limited literature with comparative clinical-radiological and morphometric data of potential prognostic relevance.

Meningiomas are the most common primary intracranial tumors, showing highly heterogeneous behavior and clinical outcomes. While the majority are benign, about one in five meningiomas are classified as higher grade (WHO Grade II–III), characterized by a more aggressive, treatment-resistant pathology. Although surgical resection remains the first-line therapy, peptide receptor radionuclide therapy is emerging as a novel and promising option for advanced, multifocal, or recurrent disease. The theranostic paradigm allows simultaneous detection and treatment of somatostatin receptor-expressing lesions using a single radiopharmaceutical. In this review, we explore the evolving role of PRRT in the management of meningiomas. We provide an integrated overview of preclinical findings—including radiosensitization mechanisms—and summarize the rapidly expanding clinical literature, which in recent years has grown both in patient numbers and in methodological sophistication. Particular emphasis is placed on advances in dosimetry, quantitative imaging, and radiomics, which are beginning to refine patient selection and improve response prediction. Together, current evidence highlights the therapeutic potential of radionuclide therapy in aggressive or refractory meningiomas and underscores the need for further prospective trials to define its optimal clinical application.