Listeria Brainstem Encephalitis in Small Ruminants: Correlation of Magnetic Resonance Imaging and Histopathology.

Abstract

Listeria Brainstem Encephalitis in Small Ruminants: Correlation of Magnetic Resonance Imaging and Histopathology Christina Stahl1, Anna Oevermann2, Daniela Gorgas1 1Clinical Radiology, Department of Clinical Veterinary Medicine, Vetsuisse-Faculty, University of Bern, Switzerland 2Neurocenter, Department of Clinical Research and Veterinary Public Health, Vetsuisse-Faculty, University of Bern, Switzerland Abstract Brainstem encephalitis is an intriguing form of Listeria monocytogenes central nervous system (CNS) infection in humans and ruminants and has a high fatality rate. However, intra vitam diagnosis remains difficult in both species (1, 2). We performed MRI of affected small ruminants, in which Listeria brainstem encephalitis is a common CNS disease, and correlated MRI features with histopathology in order to define MRI criteria for the diagnosis of listeria brainstem encephalitis. Fifteen small ruminants (nine sheep, six goats) with listeriosis underwent MRI examination of the brain using a 0.3 T system (five animals) and 1.0 T system (ten animals) including T2w, FLAIR and T1w sequences pre and post Gadolinium administration. Listeria brainstem encephalitis was confirmed by histopathology, and histopathological changes were correlated to MRI features. On MRI, lesions were best visualized in T2-weighted sequences. In all animals they were characterized by asymmetric increased signal intensity in the rhombencephalon in T2w and FLAIR sequences. The lesions showed a variable pattern and distribution, ranging from patchy with ill defined borders to diffusely affecting the entire cross-sectional area of the brainstem. Few animals had lesions in the diencephalon (three animals), whilst histopathologically detectable lesions commonly extended to the diencephalon and involved cranial nerve roots (twelve animals). The lesions were iso- to mildly hypointens in T1w sequence. Mild to moderate patchy or ring-like contrast uptake was observed in the rhombencephalon of five animals (one sheep, four goats), which showed vascular damage and perivascular fibrin accumulation on light microscopy. In the brainstem, the asymmetric T2-hyperintense lesions observed by MRI correlated well with the inflammatory infiltrates observed in histopathology (3). However, lesions in the diencephalon, cranial nerves and meninges of rostral brain areas were rarely detected by MRI, indicating that MRI underestimates involvement of the rostral brain and brain associated structures. Contrary to reported human cases of neurolisteriosis (4), contrast uptake was an inconsistent finding occurring in the rhombencephalon of only five animals.