Clinicopathologic Features and Magnetic Resonance Imaging Findings in 24 Cats With Histopathologically Confirmed Neurologic Feline Infectious Peritonitis

Crawford, A.H.; Stoll, A.L.; Sanchez-Masian, D.; Shea, A.; Michaels, J.; Fraser, A.R.; Beltran, E.

The severity of FIP appears to be determined primarily by host susceptibility and immune responses, as well as by virus strain. 5 We recognized 3 clinical syndromes based on the neurolocalization: a T3-L3 myelopathy, a central vestibular syndrome, and multifocal CNS disease. The cats that were presented with a T3-L3 myelopathy had neurologic deficits confined to the pelvic limbs, meningeal contrast enhancement of the spinal cord and, where imaged, the brainstem on MRI, and histopathologic lesions that consisted of pyogranulomatous or lymphoplasmacytic infiltration into the meninges of the spinal cord and brainstem. Cats with central vestibular syndrome or multifocal CNS disease typically had more severe neurologic deficits and more extensive MRI lesions with ventriculomegaly, mass effect, and more diffuse contrast enhancement affecting the ependyma, choroid plexuses, and meninges of the caudal cranial fossa that often extended to the third and lateral ventricles. Furthermore, the height of the lateral and fourth ventricles increased with worsening histopathologic lesion severity. Thus, the severity of the clinical presentation reflected the severity of the lesions detected by MRI and histopathology. Although the diagnostic utility of the proposed lesion grading schemes requires validation, the results of our case series suggest that MRI is a both sensitive tool to identify vasculitis and secondary ventriculomegaly in neurologic FIP as well as an accurate indicator of the extent of the histopathologic changes. By evaluating the severity of the clinical presentation with the extent of the MRI abnormalities, a prediction of the likely concurrent histopathologic lesions can be made.