Obstructive hydrocephalus in a five-year-old German shepherd dog with Pseudomonas aeruginosa ventriculitis.

Introduction / Purpose: This report describes clinical, MRI and necropsy findings of bacterial Pseudomonas aeruginosa ventriculitis and meningitis and associated obstructive hydrocephalus internus in a dog. Methods: A five-year-old male neutered working German Shepherd Dog presented to an emergency hospital for acute onset and rapid progression of obtundation, vertical nystagmus, and ataxia. A brain MRI was performed using a 1.5 T scanner including: T2-weighted, T1-weighted, T1-STIR, T2-FLAIR, T2-GRE, T1 3D GRE and T1- weighted post-contrast series. CSF culture and cytology was obtained after the MRI. The patient was euthanized and a necropsy was performed. Culture of fresh-frozen brain tissue was collected at necropsy. Results: MRI results exhibited severe obstructive hydrocephalus and cerebellar herniation through the foramen magnum. Hyperintensity of the lining of the ventricular system was present on a T2-weighted FLAIR sequence, supporting ventricular obstruction. There were subtle FLAIR hyperintensities along the dorsal cerebral cortex and mild meningeal contrast enhancement. Necropsy and histopathology revealed hydrocephalus internus, cerebellar herniation, ventriculitis and meningitis. A moderate yield of Pseudomonas aeruginosa was detected on cerebrospinal fluid and brain tissue culture. Discussion / Conclusion: Pseudomonas aeruginosa central nervous system infection has been reported with clinical symptoms and MRI findings in humans similar to this dog. The few canine cases of encephalitis involving Pseudomonas aeruginosa reported in dogs were all described with evidence of external inoculation such as otitis interna, media and migrating nasal foreign bodies. Bacterial encephalitis should be considered as a differential for obstructive hydrocephalus internus in dogs.