Case Report: Imaging and pathological features of compartmentalized subdural empyema and pachymeningitis within pre-existing porencephaly in a dog.

A 2-year-old Golden Retriever was presented with progressive intracranial signs. Neurological examination was consistent with multifocal brain disease. Magnetic resonance imaging (MRI) revealed encephaloclastic porencephaly lesions, which were worse on the right side, as well as changes within the fluid compartments, including incomplete fluid-attenuated inversion recovery (FLAIR) signal suppression, ring-like T1-weighted (T1W) contrast enhancement, and increased post-contrast FLAIR hyperintensity without restricted diffusion. Susceptibility-weighted imaging (SWAN) susceptibility was noted through the septations of the fluid compartments, and significant pachymeningeal and leptomeningeal thickening and contrast enhancement were observed. The changes were consistent with infection of the porencephalic fluid compartment with hydrocephalus ex vacuo. Moderate syringohydromyelia was observed. Intracranial cerebrospinal fluid samples were collected, and analysis showed normal cerebrospinal fluid (CSF) from the left side and neutrophilic inflammation consistent with empyema from the right fluid compartment. Despite aggressive treatment, the patient declined neurologically and was euthanized. Necropsy confirmed subdural empyema with pachymeningitis, restricted mainly to the right hemisphere. This report is a novel presentation and description of the imaging and necropsy findings of unilateral subdural empyema within pre-existing encephaloclastic pathology.