Tuberculous brain abscess mimicking a neoplastic lesion in a patient with well-controlled human immunodeficiency virus infection: illustrative case.

backgroundTuberculous brain abscess is a rare manifestation of CNS tuberculosis, typically occurring in patients with significant immunosuppression. These lesions may present as solitary ring-enhancing masses and can radiographically resemble neoplastic processes, creating diagnostic and management challenges. OBSERVATIONS: A 43-year-old man with well-controlled human immunodeficiency virus (HIV) infection and a remote history of treated pulmonary tuberculosis presented with progressively worsening unilateral headaches. MRI demonstrated a small, lobulated, peripherally enhancing posterior temporal lobe mass adjacent to dominant-hemisphere language cortex without surrounding edema, raising concern for a neoplastic lesion. Given the progressive symptoms and eloquent location, the patient underwent awake craniotomy with language mapping and gross-total resection. Histopathological evaluation revealed a chronic abscess with granulomatous inflammation, and acid-fast staining and polymerase chain reaction confirmed Mycobacterium tuberculosis, establishing the diagnosis of tuberculous brain abscess. The patient recovered without new neurological deficits and showed clinical improvement at follow-up. LESSONS: Tuberculous brain abscess can occur even in patients without overt immunodeficiency, including those with well-controlled HIV infection. Because imaging findings may overlap with neoplastic lesions and systemic infectious features may be absent, maintaining a broad differential diagnosis and pursuing timely tissue confirmation are essential to guide appropriate management and avoid delays in treating either infection or malignancy. https://thejns.org/doi/10.3171/CASE26178.