Beyond the Pia Mater: A Case Report of a Rare Exophytic Hemispheric Grade-3 Astrocytoma

Gliomas account for approximately 60% of all primary central nervous system (CNS) neoplasms, typically exhibiting growth confined within the cerebral parenchyma. However, exophytic gliomas, a rare subset, challenge this conventional pattern by breaching the pia mater and extending into the subarachnoid space. We herein report the case of a 38-year-old female patient with an isocitrate dehydrogenase (IDH)-mutant, grade-3 astrocytoma exhibiting an exophytic growth pattern, an extremely uncommon manifestation in hemispheric gliomas. The patient presented with a 10-day history of progressive left brachial monoparesis and monoparesthesia, accompanied by sudden-onset aphasia. Magnetic resonance imaging scans revealed a lesion with unique radiological characteristics, including the T2-weighted/fluid-attenuated inversion recovery (FLAIR) mismatch sign, restricted diffusion, and gadolinium enhancement, consistent with high cellularity and neoangiogenesis. Histopathological findings confirmed a grade-3 IDH-mutant astrocytoma. The patient underwent microsurgical resection with neuronavigation and intraoperative neurophysiological monitoring, achieving complete resection of the exophytic component. Postoperatively, she recovered without complications and commenced adjuvant therapy with temozolomide and radiotherapy. This case highlights the clinical and radiological complexities of exophytic gliomas, emphasizing the importance of multidisciplinary approaches for accurate diagnosis and management. It also underscores the need for further studies to explore the underlying mechanisms and optimize therapeutic strategies for these rare tumors.