The photo is from an adult, domestic long haired, barn cat who was euthanized after losing weight and exhibiting incoordination and other neurologic signs. Another cat with similar signs recently died. Rabies examination was negative.
Kidney: Pyogranulomatous vasculitis and interstitial nephritis
Grossly, there are multifocal to coalescing tan foci that are rimmed by hemorrhage. These foci track the vasculature and represent suppurative and granulomatous inflammation that extends from blood vessels to the cortical interstitium of the kidney. Microscopically, blood vessels are often occluded with fibrin thrombi, around which there is frequent necrosis.
These changes are consistent with the dry, non-effusive form of feline infectious peritonitis (FIP). FIP is caused by a mutated enteric coronavirus that is specific to cats. The neurologic signs in this case are due to the same inflammation in the kidneys being present in the meninges and ventricles of the brain.