Adult Thoracic Intramedullary Pilocytic Astrocytoma With Prominent Glomeruloid Microvascular Proliferation Diagnosed by Integrated Molecular Analysis A Case Report

Background: Pilocytic astrocytoma (PA) is a circumscribed, World Health Organization (WHO) grade 1 glioma that predominantly affects children and is rare in the adult spinal cord. Diagnostic difficulty arises when adult spinal PAs exhibit radiological or histopathological features typically associated with high-grade gliomas, particularly prominent microvascular proliferation, which may result in tumor overgrading and overtreatment. Case Description: We report a 20-year-old male presenting with progressive thoracic myelopathy and evolving paraplegia. Magnetic resonance imaging demonstrated diffuse intramedullary spinal cord expansion from T2 to T9 with a focal, avidly ring-enhancing lesion at T6–7, raising concern for a high-grade intramedullary glioma. Surgical resection was undertaken, guided by the presumed malignant nature of the lesion. Histopathology revealed classic pilocytic architecture with abundant Rosenthal fibers but also striking glomeruloid microvascular proliferation. Integrated molecular analysis showed retained H3K27me3 expression, wild-type BRAF V600E, and absence of TERT promoter mutation, establishing a final diagnosis of pilocytic astrocytoma, CNS WHO grade 1. Postoperatively, the patient developed complete spinal cord injury but achieved functional independence in wheelchair mobility and autonomous bladder management through structured rehabilitation. Conclusion: This case highlights a critical diagnostic pitfall in adult intramedullary spinal tumors: microvascular proliferation in pilocytic astrocytoma does not equate to malignant biological behavior. Integrated molecular diagnostics—particularly assessment of H3K27 status—are essential to avoid misclassification, inappropriate treatment escalation, and irreversible neurological morbidity.