Purely cystic meningioma: extremely rare clinical and radiographic mimic of intra-axial glioblastoma multiforme with systematic review of the literature. Illustrative case.

backgroundPurely cystic meningiomas are extremely rare extra-axial neoplasms that can mimic aggressive malignancies, like glioblastoma multiforme (GBM), because radiologically and intraoperatively they lack a visible solid component and demonstrate postcontrast enhancement and significant vasogenic edema. The authors present a case of a purely cystic intra-axial meningioma mimicking GBM with an accompanying systematic review of the literature. OBSERVATIONS: An 84-year-old female presented with expressive dysphasia. MRI revealed a 3-cm inhomogeneously enhancing intra-axial left temporal lobe mass with apparent MRI presentation of central necrosis, suggesting a high-grade glioma. Intraoperatively, the lesion appeared vascular and infiltrative like a GBM; however, histopathological and immunohistochemical analyses (somatostatin receptor 2 antigen positive, progesterone receptor positive, glial fibrillary acidic protein negative) confirmed an angiomatous meningioma (WHO grade 1). Postoperatively, the patient's symptoms resolved, and 10 years of annual follow-up MRI studies confirmed no recurrence. Only 3 other purely cystic meningioma cases (extra-axial) were identified in the literature. LESSONS: Cystic meningiomas are rarely GBM "imitators." Surgeons should consider cystic meningioma when classic radiological hallmarks are absent. Despite an aggressive imaging profile, these tumors are biologically and clinically benign. Gross-total resection remains the gold-standard treatment, offering excellent long-term prognosis and the potential for a permanent cure. This case highlights the need for histological tissue diagnosis before final treatment plans are considered. https://thejns.org/doi/10.3171/CASE26438.