Hippocampal necrosis and sclerosis in cats: A retrospective study of 35 cases

Hippocampal necrosis and hippocampal sclerosis in cats is a neuropathological entity which is a major concern in feline epilepsy. The aim of our study was to identify associated pathologic brain lesions possibly serving as aetiological triggers in this condition. Therefore, the formalin-fixed and paraffin waxembedded brain tissue of 35 cats diagnosed with hippocampal necrosis or sclerosis was examined retrospectively. In 26 cats inflammatory infiltrates could be found in the hippocampus or adjacent brain regions. Fifteen out of these animals demonstrated mild to moderate infiltrations by lymphocytes and complement deposition in the hippocampus similar to human limbic encephalitis, seven showed unspecific, predominantly non-suppurative inflammation, and two demonstrated suppurative inflammation of the hippocampus or adjacent brain regions. Additionally, one cat was diagnosed with central nervous manifestation of feline infectious peritonitis virus and another one with cerebral Toxoplasma gondii infection. Intracranial neoplasia was present in five cases altogether. Three of them comprised meningioma which was present additionally to lesions resembling limbic encephalitis in two cases, and a dentate gyrus alteration in one case. The other two tumour-associated cases comprised oligodendroglioma. Structural alterations of the dentate gyrus together with hippocampal sclerosis were encountered in three cases in total. Besides the case associated with a meningioma, one case demonstrated lesions resembling limbic encephalitis. A vascular infarct in the temporal lobe was encountered in one cat. In four cases no lesions other than hippocampal necrosis or sclerosis were found. The involvement of feline immunodeficiency virus infections, which may be able to produce hippocampal lesions, was not encountered in the cats examined.

Hippocampal Necrosis in a Cat from Australia

This paper reports findings from a feline case of hippocampal necrosis. A seven-year-old neutered female cat was seen with a history of behavioural change followed by complex focal seizures. The cat was severely pyrexic on presentation and anisocoria was present. It was treated with cooling, intravenous fluid, and phenobarbitone administration which was later changed to levetiracetam. An MRI was performed and revealed findings of a hypointense T1 and hyperintense T2 signal in the hippocampus and inferior temporal gyrus with mild gadolinium uptake, findings which were consistent with previous cases of hippocampal necrosis. The cat was witnessed to vomit and aspirate 24 hours after diagnosis leading to cardiac arrest and death. Postmortem examination revealed a subacute degenerative encephalopathy involving the hippocampus.