A Case Report of Listeria monocytogenes Abscesses Presenting as Cortically Predominant Ring-Enhancing Lesions.

Introduction: Listeria monocytogenes, a common cause of bacterial meningitis, rarely involves the central nervous system (CNS) in the form of multiple cerebral ring-enhancing lesions.

Methods: An 81-year-old woman with rapidly progressive decline in her mental status in the setting of multiple cortically predominant ring-enhancing lesions was transferred to our institution. A mild upper respiratory tract infection and diarrhea symptoms preceded the mental status deterioration. Her past medical history is significant for type 2 diabetes mellitus. In light of the patient's age, the presence of hyponatremia and the history of diabetes mellitus, the empiric antimicrobial treatment was modified to include ampicillin, meropenem, vancomycin, voriconazole and pyrimethamine/sulfadiazine to prevent opportunistic infections. Intravenous dexamethasone was added due to significant perilesional vasogenic edema.

Results: The patient presented with stupor, but neither fever nor leukocytosis. CSF results were significant only for a mildly elevated protein level. The report of a repeat brain MRI was as follows: large areas of high FLAIR signals and tubular/lobulated/ring enhacement in bifrontal regions with a smaller focus in the left anterior midbrain, indicating for underlying multicentric glioma or multicentric primary CNS lymphoma. A brain biopsy, however, revealed an early abscess formation caused by a L. monocytogenes infection.

Conclusion: A high index of suspicion in patients with risk factors for this infection is key to ensure the timely initiation of appropriate empirical antibiotic therapy in the setting of cerebral ring-enhancing lesions. Intravenous ampicillin is the treatment of choice, but meropenem represents a valid alternative.