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Introduction: Foreign body-associated encephalitis is a rare condition and can be observed mainly after severe, penetrating trauma of the skull, nose or ears.
Materials and Methods: A 2-year-old Hungarian vizsla dog was presented with multiple epileptiform seizures approximately 6 weeks after hyperthermia of unknown origin. Magnetic resonance imaging revealed intra-axial changes in the right occipital lobe. Analysis of the cerebral spinal fluid (CSF) identified severe, neutrophilic to mixed cellular pleocytosis and highly increased protein, suggestive of meningoencephalitis. Bacterial culturing of the CSF and 16S rRNA gene sequencing failed to reveal bacterial involvement. The dog was humanely destroyed because of the poor prognosis.
Results: A 1.75 cm long, linear, plant-like foreign body, penetrating 1.45 cm into the cerebral parenchyma was associated with a severe and focally extensive chronic pyogranulomatous meningoencephalitis. Further histopathological lesions included unilateral rhinitis with focally extensive fibrosis on the right. The perineural connective tissue of the left optic nerve had mild multifocal lymphoplasmacytic infiltrates accompanied by macrophages and few multinucleated giant cells.
Conclusions: Despite the size of the foreign body, a migration tract was not identified. Non-traumatic routes of entry may involve nasal migration, the inner otic canal, perforation of the pharyngeal soft tissue, the Foramen magnum or a periocular pathway, for which, in this case, the histological findings in the nasal and perineural tissue may be consistent. Encephalitis due to migrating plant material, most frequently involving a grass awn, with or without bacterial infection, is an unusual lesion, presenting a challenging ante-mortem diagnosis.