Investigating Intracranial Causes of Seizures in Cats: MRI, CSF and Infectious Disease Testing

Once reactive causes have been ruled out, attention shifts towards the brain. Advanced imaging can identify structural abnormalities, while cerebrospinal fluid (CSF) analysis and targeted infectious testing may provide additional information when inflammatory, infectious or neoplastic disease is suspected. 

Choosing Between CT and MRI 

Both CT and MRI have a role, but their clinical strengths differ. 

CT may be more accessible and can sometimes be performed under sedation. It is useful for detecting certain neoplasms and is particularly valuable in trauma cases for identifying skull fractures and acute haemorrhage. Its main limitation is poorer definition of the brain compared with MRI. 

MRI generally requires general anaesthesia and is more costly and time-consuming but provides substantially better soft tissue resolution. It offers detailed assessment of the brain and meninges and can identify changes consistent with structural, metabolic, and neurodegenerative disease^[1],[2]. 

For these reasons, MRI is the imaging modality of choice for most cats with epileptic seizures. 

The choice should nevertheless remain clinically appropriate. CT can be particularly useful when osseous abnormalities or acute traumatic changes are a priority, whereas MRI provides more detailed assessment of intracranial soft tissues. 

When is CSF Analysis Useful? 

Imaging findings can help determine whether CSF sampling is warranted. 

CSF analysis can be particularly useful when inflammatory or infectious disease is suspected. Some neoplastic processes, including lymphoma, may also be detected through CSF, although neoplastic cells are uncommon even in cats with central nervous system lymphoma. 

CSF findings can help establish whether inflammation is present, but they are often non-specific for the underlying disease. 

In cats with epileptic seizures, collection from the cerebellomedullary cistern, or cisterna magna, is typically preferred. One reported finding is particularly relevant when interpreting apparently normal investigations: only 4.6% of cats with normal brain MRI or MRI showing only hippocampal changes had abnormal CSF findings^[3]. 

Interpreting the CSF Sample 

Normal CSF is clear, colourless and largely acellular, with fewer than five nucleated cells/μl considered within normal limits. Protein concentration should be below 27 mg/dl in a cisternal sample^[2]. 

Changes in appearance can provide additional clues. Increased turbidity may indicate a highly cellular sample, whereas xanthochromia can reflect previous haemorrhage. Red discoloration is often attributable to iatrogenic blood contamination^[2]. 

Albuminocytologic dissociation, an increased protein concentration without an increased nucleated cell count, is non-specific and may occur with inflammatory, vascular, neoplastic, and degenerative processes. 

Increased nucleated cell counts and cytological evaluation can be particularly useful when inflammatory or infectious disease is suspected. Ideally, CSF should be analysed shortly after collection, so laboratories should be contacted in advance regarding preferred collection tubes and fixation methods. 

Add Targeted Infectious Disease Testing 

The clinical history, imaging findings, and geographical or travel context should guide infectious disease testing. 

Bacterial culture or PCR can be performed on CSF, including testing for feline infectious peritonitis (FIP) or Toxoplasma gondii. Serology provides a non-invasive option for T. gondii testing. 

Depending on geographical location and travel history, fungal testing for organisms such as Cryptococcus gattii or Blastomyces dermatitidis may also be relevant. 

Aberrant parasitic migration can produce neurological signs, including seizures. Cuterebra species are particularly relevant, although Dirofilaria immitis can also be involved^[2],[4]. 

FeLV and FIV status should also be checked. Although there are no published reports supporting either virus as a direct cause of epileptic seizures, both can compromise immunity and increase the risk of clinically relevant infections, while both appear to be associated with lymphoma, which can involve the central nervous system^[2]. 

Urinalysis and urine culture and sensitivity may also be useful because bacteriuria has been associated with encephalopathy in cats, with epileptic seizures reported in these cases^[5]. 

Clinical Bottom Line 

After reactive causes have been excluded, MRI provides the most comprehensive assessment of intracranial disease in most epileptic cats, while CSF analysis and targeted infectious testing can add diagnostic information in selected cases. Because CSF collection carries risks, including potential inadvertent neural injury, sampling should be considered only after weighing the expected diagnostic benefit against those risks.

References:

1. Miguel-Garcés M, Gonçalves R, Quintana R, Álvarez P, Beckmann KM, Alcoverro E, Moioli M, Ives EJ, Madden M, Gomes SA, Galban E. Magnetic resonance imaging pattern recognition of metabolic and neurodegenerative encephalopathies in dogs and cats. Frontiers in Veterinary Science. 2024 Jul 30;11:1390971. https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1390971/pdf
2. Sivolapenko D, Lowrie M. Epileptic seizures in cats: practical approaches to diagnosis. Journal of Feline Medicine and Surgery. 2026 Feb;28(2):1098612X251407905. https://journals.sagepub.com/doi/pdf/10.1177/1098612X251407905
3. Majercikova R, Rütgen BC, Luckschander-Zeller N, Lörincz BA, Pakozdy A. Diagnostic value of cerebrospinal fluid analysis in epileptic cats with unremarkable brain MRI or hippocampal signal changes only. Journal of Feline Medicine and Surgery. 2023 Mar;25(3):1098612X231158573. https://journals.sagepub.com/doi/pdf/10.1177/1098612X231158573
4. James FM, Poma R. Neurological manifestations of feline cuterebriasis. The Canadian Veterinary Journal. 2010 Feb;51(2):213. https://pmc.ncbi.nlm.nih.gov/articles/PMC2808293/pdf/cvj_02_213.pdf
5. Crawford AH, Cardy TJ. Is there a link between bacteriuria and a reversible encephalopathy in dogs and cats?. Journal of Small Animal Practice. 2020 Aug;61(8):467-74. https://onlinelibrary.wiley.com/doi/pdf/10.1111/jsap.13178