Imaging of the brain and surrounding tissue is necessary to eliminate other intracranial causes of seizure. Magnetic resonance imaging (MRI) and computed tomography (CT) can both be used to identify (or rule out) structural brain disease. However, a normal CT scan does not exclude the possibility of cerebral pathology. Inflammatory or infectious CNS diseases are rarely detectable with MRI or CT and if these are suspected a CSF sample may be required for diagnosis. MRI is most likely to be useful in animals in which onset of seizures occurs after the age of 6 years, or those in which seizures are refractory to standard treatments. In addition to identifying an underlying cause of seizures, MRI or CT is required as an aid to treatment planning (radiotherapy or surgery) for intracranial masses. Skull radiography is rarely of any value.
Screening thoracic and abdominal radiographs are used to help rule out systemic conditions causing seizures. Ultrasonography may be useful to further evaluate suspected cardiovascular or metabolic disease, eg portosystemic shunts.
Although it is unlikely that the veterinarian in practice will have to undertake MRI or to interpret the scans, it is useful to have an understanding of what can be seen and what diagnoses can be made using this modality. Further information on the subject can be found here.
Image: MRI scan of the brain after contrast injection (gadolinium) in a Boxer with a glioma. - courtesy of Laurent Garosi, Davies Veterinary Specialists.
There are many clinical indications for referral but imaging referrals are generally made when a second opinion is required on results and findings already obtained or for further investigation using more specialised equipment not available to the general practitioner. MRI is important for investigation of central nervous system disease – the brain is hard to image accurately with any other modality.
Bush W, Bush CS, Darrin E, Shofer F et al (2002) Results of cerebrospinal fluid analysis, neurologicz examination findings, and age at the onset of seizures as predictors for results of magnetic resonance imaging of the brain in dogs examined because of seizures: 115 cases (1992-2000). JAVMA 220(6), 781-784. - PubMed -
Smith PM, Talbot CE, Jeffery ND (2008) Findings on low-field cranial MR images in epileptic dogs that lack interictal neurological deficits. Vet J. 176(3), 320-325. - PubMed -
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