A Culture-negative Refractory Brain Abscess Presumed to be Caused by Listeria Monocytogenes via a Pulmonary Arteriovenous Malformation.

A 59-year-old man presented with progressive fever, headache, and right hemiparesis. Brain magnetic resonance imaging revealed an elongated tubular rim-enhancing lesion extending along the corticospinal tract. The lesion showed a selective radiological response to ampicillin and trimethoprim-sulfamethoxazole but relapsed after treatment discontinuation. Repeat blood cultures, cerebrospinal fluid cultures, polymerase chain reaction testing, and autopsy revealed no identifiable pathogens. Based on the characteristic tract-based imaging features and selective antimicrobial response, this case was clinically considered a probable Listeria monocytogenes brain abscess. Retrospective imaging revealed a small pulmonary arteriovenous malformation that may have contributed to the brain abscess formation.