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.

Despite the variable severity in neurologic deficits among the 3 identified clinical syndromes, all cases were euthanized within a median of 2 days of referral. This finding may suggest that the severity of neurologic deficits on presentation does not substantially influence the decision for euthanasia, but rather that the major factor in the decision is the positive diagnosis of FIP and its associated grave prognosis. 1, 4, 5, 11 Enlargement of the ventricular system was detected in 20 cats, usually involving multiple ventricles and the mesencephalic aqueduct. Marked vasculitis with secondary accumulation of inflammatory exudate within the mesencephalic aqueduct and lateral apertures obstructs normal CSF flow leading to increased intraventricular pressure and secondary ventricular distension. 12 The FLAIR sequences identified T2W hyperintensities surrounding the lateral ventricles in 15 cats. These imaging characteristics are consistent with interstitial edema, the formation of which has been attributed to transependymal absorption of CSF that follows the pressure gradient from the ventricle to the parenchyma. 12 As previously reported, the distribution of ependymal contrast enhancement appeared to correspond to the degree of ventricular enlargement, with the third and fourth ventricles most commonly affected. 5 Magnetic resonance imaging identified intramedullary T2W hyperintensity, consistent with syringomyelia, within the cervical spinal cord in 17 cats. However, syringomyelia was not observed on postmortem examination, presumably due to failure to extensively examine the cervical spinal cord. Syringomyelia has been detected in cats with neurologic FIP previously and is presumed to result from the extensive inflammatory cell infiltrates obstructing CSF flow along the central canal of the spinal cord, which may be exacerbated by increased intracranial pressure altering normal CSF dynamics. 13, 14 In a case series of 4 cats with syringomyelia of various etiologies, each was found to have ventriculomegaly with evidence of mass effect including midline shift and foramen magnum herniation. 13 Syringomyelia also has been reported in a cat with multiple intracranial meningiomas, 15 and in a cat with severe congenital hydrocephalus. 16 Thus, identification of syringomyelia in a cat should alert the clinician to the possibility of intracranial pathology causing increased intracranial pressure.