MRI Features of Ventricular Empyema Caused by Escherichia coli in a Dog.

Ventricular empyema is a rare but severe complication of central nervous system (CNS) infections in dogs, with a poor prognosis due to limited treatment options. A 6-year-old intact female Pomeranian (1.9 kg) presented with acute-onset nonambulatory tetraparesis, spontaneous nystagmus, and head tilt. Hematological analysis revealed leukopenia with neutropenia and elevated C-reactive protein (CRP), suggesting systemic inflammation. MRI showed ventricular dilation with distinct stratified fluid-fluid levels. The dependent material was hypointense on T2-weighted (T2W) images and unsuppressed on T2W FLAIR (fluid-attenuated inversion recovery). It was hyperintense on diffusion-weighted imaging (DWI) and hypointense on apparent diffusion coefficient (ADC) maps, consistent with restricted diffusion. Its position changed with repositioning, suggesting a gravity-dependent nature. Cervical spinal cord MRI revealed a T2W hyperintense, contrast-enhancing intramedullary lesion from C3 to C7. Cerebrospinal fluid (CSF) analysis confirmed severe neutrophilic pleocytosis with numerous bacilli, later identified as Escherichia coli. Despite antibiotic therapy, the patient's condition deteriorated, leading to euthanasia. No extracranial infectious source was identified, supporting hematogenous dissemination as the most plausible route of infection. This is the first reported case of E. coli-induced ventricular empyema in veterinary medicine confirmed via advanced imaging. This report highlights the diagnostic role of DWI/ADC mapping and the novel use of patient repositioning to assess intraventricular material dynamics, underscoring the need for further research into advanced imaging and treatment strategies.