CSF After a Normal MRI? Study Says Rethink Routine Testing in Pets

Usefulness of Cerebrospinal Fluid Analysis in Dogs and Cats with Suspected Intracranial Disease and Normal Magnetic Resonance Imaging

Susana R. Monforte Monteiro, Luisa De Risio, Lisa Alves, An E. Vanhaesebrouck

Background:
Cerebrospinal fluid (CSF) analysis is a common diagnostic tool in veterinary neurology, used alongside MRI to investigate intracranial disease. Whether routine CSF sampling is beneficial after a normal MRI remains debated, particularly given the small but real risks of the procedure. This study aimed to determine whether CSF analysis meaningfully changes diagnosis or treatment in dogs and cats with suspected intracranial disease but normal MRI findings.

Methods:
A retrospective multi-center review was conducted on 593 animals (533 dogs, 60 cats) seen between 2015–2019 at two UK veterinary referral centers. Inclusion criteria were clinical signs consistent with intracranial disease, full neurological examination, normal high- or low-field brain MRI (including pre- and post-contrast T1-weighted sequences), and CSF analysis from the cerebellomedullary cistern. Data on neurological status, final diagnosis, treatment, and outcomes were analyzed.

Results:
Of the 593 animals, 17 dogs (3%) had abnormal CSF despite normal MRI; no cats had abnormal CSF. Abnormalities included pleocytosis (n=9) and/or hyperproteinorrachia (n=10). Only five dogs (0.8% overall) had diagnoses or treatments altered by CSF findings—three were diagnosed with inflammatory brain conditions and two received corticosteroids based on abnormal results without definitive diagnosis. All but one of these five dogs had abnormal neurological examinations. Dogs with abnormal neurological exams were nine times more likely to have CSF results that changed management compared to neurologically normal dogs.

Limitations:
This was a retrospective study with variable MRI equipment, and without histological confirmation of diagnoses. CSF sampling and interpretation decisions were clinician-dependent, and the small feline sample size limited conclusions for cats. Subtle lesions may have been missed on MRI, particularly with low-field units.

Conclusions:
Routine CSF analysis after a normal MRI rarely changes diagnosis or treatment, especially in neurologically normal dogs and cats. Its use is more justified in patients with abnormal neurological examinations or high suspicion of inflammatory brain disease. Clinical suspicion should guide CSF collection rather than a blanket approach following normal MRI.

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