Cryptogenic brain abscess mimicking brain tumor in an immunocompetent young adult

Brain abscess is a rare but potentially fatal intracranial infection. In immunocompetent young adults, cryptogenic brain abscesses may mimic brain tumors and delay diagnosis. We report a 28-year-old man presenting with acute left-sided weakness, headache, and seizures. Initial evaluation suggested an intracranial tumor. Magnetic resonance imaging revealed a ring-enhancing parietal lesion with edema and mass effect. No primary source of infection was identified, and laboratory tests showed elevated inflammatory markers without leukocytosis. Craniotomy with excision and drainage confirmed a brain abscess, while cultures were negative. Empirical antibiotics were administered with regimen adjustment for metronidazole allergy, resulting in full neurological recovery. This case highlights that cryptogenic brain abscesses can closely resemble intracranial tumors in immunocompetent patients. Early recognition and prompt intervention are essential for favorable outcomes.