Leptomeningeal and Ependymal Seeding of a High-Grade Glioma Following Ventricular Opening and Carmustine Wafer Implantation: A Case Report Highlighting a Diagnostic Dilemma.

Leptomeningeal and ependymal seeding (LES) is an uncommon but devastating complication of high-grade gliomas, and its incidence appears to be rising as improved multimodal treatment prolongs patient survival. Intraoperative ventricular entry and repeated surgery are well-established risk factors, and their coexistence with carmustine wafer implantation raises technical and diagnostic questions that remain underexplored in the literature. We report the case of a 37-year-old man with a right parieto-occipital WHO grade III anaplastic astrocytoma, initially treated with gross total resection and standard chemoradiotherapy. Following local recurrence at 19 months and a second resection with cranioplasty, the patient developed advanced tumor progression 17 months later that required a third surgery, during which an incidental opening of the lateral ventricle occurred; the defect was sealed with Gelfoam (Pfizer Inc., New York, United States) and Surgicel (Ethicon, Inc., Raritan, New Jersey, United States), and eight carmustine wafers were subsequently implanted in the surgical bed. Definitive histopathology documented malignant transformation to glioblastoma (WHO grade IV) with mutant IDH1. Two months later, the patient developed acute neurological deterioration with diffuse ependymal and leptomeningeal enhancement; because lumbar puncture was relatively contraindicated, magnetic resonance spectroscopy (MRS) directed at the hypothalamic and cervical regions of abnormal enhancement showed a pattern highly suggestive of active neoplastic seeding (choline/N-acetylaspartate (Cho/NAA) 8.0, choline/creatine (Cho/Cr) 3.2). Despite high-dose corticosteroid therapy, the patient died of progressive motor and respiratory decline. This case illustrates the diagnostic dilemma that arises when intraoperative ventricular entry and subsequent carmustine wafer implantation coincide in the same procedure: distinguishing true leptomeningeal tumor seeding from carmustine-induced chemical leptomeningitis, since both can produce an indistinguishable enhancement pattern on conventional MRI. We also discuss the clinical rationale for using carmustine wafers as a local therapeutic bridge. At the same time, a patient awaits formal oncologic evaluation, a wait that is often prolonged in publicly funded health systems. We review the reported evidence on risk factors for cerebrospinal fluid (CSF) dissemination, carmustine-related complications near the ventricular system, the role of MRS when lumbar puncture is contraindicated, and the relevance of the 2021 WHO nomenclature for interpreting this case.