Brain metastasis mimicking brain abscess: illustrative case and systematic review.

backgroundDiffusion-weighted imaging (DWI) is a valuable tool in distinguishing brain abscesses from neoplastic lesions, with restricted diffusion often interpreted as indicative of infection. However, some metastatic brain lesions can mimic abscesses both radiologically and clinically, presenting a diagnostic challenge. OBSERVATIONS: A 58-year-old woman presented with confusion and was found to have multiple ring-enhancing brain lesions with uniform restricted diffusion on DWI. Initial imaging raised concern for pyogenic abscesses, and empiric antibiotics were initiated. However, systemic imaging revealed a left upper lobe lung mass, and stereotactic biopsy confirmed metastatic adenocarcinoma. The authors performed a systematic review and identified 28 studies describing metastatic lesions with restricted diffusion, most involving solitary lesions with partial restriction. Only a few described multiple lesions with partial restricted diffusion. Lung adenocarcinoma was the most common primary source. LESSONS: This case illustrates that metastatic disease can mimic abscesses on DWI, particularly when lesions are ring enhancing and diffusion restricting. In the absence of clear infectious signs, a broader differential should be considered. Clinical context, systemic imaging, and early biopsy may help clarify the diagnosis and guide appropriate management. https://thejns.org/doi/10.3171/CASE25528.