Listeria monocytogenes brain abscess: A case presentation

A 57-years-old male presented to our hospital with fever (38.5°C), weakness and vomiting. The PCR test for COVID-19 infection was negative. Neurological examination revealed neck stiffness. Brain Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) were performed. The cerebrospinal fluid (CSF) examination showed high levels of lymphocytes, protein and very low levels of glucose. Listeria monocytogenes were detectable in Gram stains of CSF and isolated from CSF cultures. The patient started antibiotic therapy with i.v. ampicillin for 4 weeks before surgery drainage.

Brain CT revealed a nonspecific hypodense lesion of the left frontal lobe (Fig 1).  Brain MRI showed two lesions located on the left cerebellar peduncle (Fig 2A) and on the left frontal lobe (Fig 2B). On T2-weighted images, the latter seemed to be formed by multiple converging radial foci (Fig 2C), which showed restricted diffusion on apparent diffusion coefficient (ADC) maps and were surrounded by vasogenic oedema (Fig 2D). The characteristic “worm-like” or “tunnel-like” enhanced formations are best depicted on T1- weighted post-contrast images, yet they were also been shown on other sequences (Fig 2E).

Listeria monocytogenes (LM) is a Gram-positive intracellular pathogen affecting especially the CNS and applying for ~30% of all LM infections (1,2). Meningitis is the most common manifestation (3).  Brain abscesses are rare and account for 1-10% of CNS listerial infections (4,5). Listeria is transmitted through the consumption of contaminated food such as seafood, meat, and vegetables. It is also considered one of the most common foodborne infections (6).

LM is a bacterium with affinity for the central nervous system. CNS manifestations of listerosis depend on the affected intracranial compartment and include meningitis, encephalitis, rhombencephalitis, meningoencephalitis and less commonly cerebral abscess. The distribution of brain abscesses in listerosis follows a unique pattern, and is usually observed in the midbrain, the pons and the medulla and to the lesser extent the supratentorial brain. At least 3 different pathways have been suggested for CNS invasion: 1) through the blood-brain and blood-choroid barriers, within infected phagocytes, 2) direct invasion of the capillary endothelium by the circulating extracellular bacteria, 3) retrograde migration into the CNS, by travelling through the axons of cranial nerves and especially along trigerminal nerve (7). The first two pathways are hematogenous and are considered the most common (8). MRI lesions in our case, were not primarily to the brain stem and consequently hematogenous spread is the most likely scenario.

Elderly and immunocompromised patients are the major risk groups. Supratentorial lesions seem to appear more frequently to immunocompromised patients (9).

Listeria abscesses seem to have a characteristic multitubular appearance, also referred to as “tunnel-like” or “worm-like” lesions, mentioned in previous case reports (4, 10, 11). These findings are also relatively specific for other limited pathogens, such as Spirometra mansoni (sparganosis) and Bukholderia pseudomallei (melioidosis) (12). In conclusion, these specific imaging findings are of major importance for early detection and treatment, which are mandatory to ensure the best prognosis.