Tumor-mimicking primary CNS vasculitis: illustrative case.

backgroundA subset of primary CNS vasculitis (PCNSV) cases can present with clinical and radiological features that closely resemble brain tumors, creating a significant diagnostic challenge for clinicians. Accurate differentiation between these entities is crucial for timely and appropriate management, as their treatment strategies and prognoses differ substantially. The authors report an illustrative case and summarize the published literature on tumor-mimicking PCNSV to show diagnostic features, treatment, and outcomes. OBSERVATIONS: This illustrative case involved a 35-year-old male initially presenting with stroke-like symptoms, whose MRI findings suggested a diffuse left hemispheric lesion concerning for glioma. Despite initial biopsies, the diagnosis remained unclear until a subsequent biopsy revealed PCNSV after a course of chemotherapy and radiation therapy. The review included 63 patients with tumor-mimicking PCNSV, with a mean age of 40 years. Common presentations were focal deficits (62%) and headaches (52%). MRI consistently showed T2/FLAIR-hyperintense lesions with variable enhancement and edema. Lymphocytic vasculitis was the predominant histological finding (76%). Most patients (92%) received high-dose steroids. Granulomatous findings were associated with lower odds of recurrence. LESSONS: Tumor-mimicking PCNSV poses a significant diagnostic challenge. Recognizing its diverse presentations is critical for prompt diagnosis and appropriate clinical management. https://thejns.org/doi/10.3171/CASE26201.