Listerial rhombencephalitis

Clinical History

A previously healthy 66-year-old female patient was diagnosed with gastroenteritis by her family doctor due to vomiting, diarrhoea and fever of 39ºC. Two days later, she was referred to our Emergency Department due to dysarthria, facial palsy, ataxia and fever of 38ºC.

Imaging Findings

Non-contrast and contrast-enhanced CT of the brain were reported as normal but a faint focal low density area was identified in the left dorsal pons retrospectively (Fig. 1). MRI performed one day later showed a symmetric hyperintensity in the mesencephalon on T2WI that extended downwards from the dorsal pons to the left middle cerebellar peduncle (Fig. 2-4). This hyperintensity was homogeneous except for a pontine hypointense area with peripheral enhancement on post-contrast T1WI that corresponded with an abscess (Fig. 5).
Other similar lesions were seen in the right middle cerebellar peduncle and ipsilateral cerebellar hemisphere that produced minimum mass effect and showed a small hypointense dot with faint ring enhancement in relation to another cerebellar abscess (Fig. 2-5).
DWI sequence showed foci of restriction in the mesencephalon, pons, medulla and right cerebellar peduncle and their respective hypointensity on ADC maps (Fig. 6).
Definitive diagnosis was obtained by blood culture.

Discussion

A. Background
Listeria monocytogenes is an anaerobic gram positive bacteria that can be found in water, vegetables and animals like birds and fish, so the main way of infection is the ingestion of contaminated food [1]. There are two ways of disease: noninvasive gastrointestinal listeriosis (that affects inmunocompetent people and causes fever and gastrointestinal symptoms) and invasive listeriosis (that affects inmunosuppressed people which present meningoencephalitis or septicemy) [1]. Listeric CNS predilection is controversial [2]. Nevertheless, several studies suggest that Listeria invades the brainstem by axonal migration from the neural pathways that connect this region with the upper gastrointestinal tract [2, 3].

B. Clinical perspective
Listeriosis evolves in two phases. The prodromal phase shows unspecific symptoms [4] which can be misdiagnosed [5] like fever, vomiting and headache [1, 4]. The neurological phase symptoms are sensory and motor deficits, ataxia and cranial nerves palsies [1, 4].

C. Imaging perspective
MRI is very important in order to identify the typical parenchymal localization, with predilection of listeriosis for the cerebellum and brainstem. It usually shows hyperintense areas on T2-weighted images in the rhombencephalon and hypointense dots with ring enhancement due to microabscesses [1, 5]. However, CT is usually normal [1, 5, 6].

D. Outcome
Listerial rhombencephalitis has a mortality rate higher than 50% [1, 5].
CSF shows an increased leukocyte count, normal glucose levels and increased protein levels [5], however, in our patient it was normal. Definitive diagnosis is obtained by culturing the microorganism in blood (as was done in our patient), CSF or another sterile fluid. Nevertheless, early diagnosis cannot be performed by the relative slow growth of the microorganism, approximately 3-4 days.

Penicillin and ampicillin are the initial treatment. Since its bactericidal activity is slow, it is advisable to combine with an aminoglycoside. Penicillin’s association with gentamicin acts synergistically against Listeria, and has become the standard of care [7].

Our patient was transferred to Intensive Care Unit in a coma and was treated with ampicillin and gentamicin. She was also connected to mechanical ventilation. After a brief improvement, although with persistent involvement of the brainstem, facial palsy and quadriplegia, she suffered from further deterioration of consciousness, so treatment was replaced by linezolid and rifampicin. After that moment she had a progressive neurological improvement until spontaneous eye opening and force recovery.

E. Take home message
Listerial encephalitis should be suspected in ataxia, sensitive or motor symptoms, cranial nerve dysfunction with rhombencephalic affectation and microabscesses in MRI.

Differential Diagnosis List

Final Diagnosis

Listerial rhombencephalitis

URL:	https://www.eurorad.org/case/13797
DOI:	10.1594/EURORAD/CASE.13797
ISSN:	1563-4086