Use of MRI in the neurologic patient
Feb 01, 2006
In contemporary veterinary medicine, magnetic resonance imaging (MRI) is an important tool in the diagnosis of neurological problems.
However, MRI does not simply display the diagnosis. Other diagnostic tests, such as survey radiographs, myelogram, serologies, cerebrospinal fluid analysis, electro-encephalography and histopathology still remain crucial in the thought process toward the definitive diagnosis.
In a recent article, 76 percent of the dogs with inflammatory cerebrospinal fluid (CSF) had detectable MR brain lesions, while 24 percent did not (C.R. Lamb et al.: Magnetic Resonance Imaging Findings in 25 Dogs with Inflammatory Cerebrospinal Fluid, Vet Radiol Ultrasound, Vol. 46, No. 1, 2005, pp 17-22). Two out of the 25 dogs with inflammatory CSF had a focal lesion, and one of these patients had neoplasia (choroid plexus papilloma). Seventeen had multifocal or diffuse lesions throughout the brain. The definitive and the tentative diagnoses for these patients included granulomatous meningoencephalitis, toxoplasmosis, neosporosis, distemper, non-specific meningitis, necrotizing fasciitis and pug encephalitis. Six dogs out of 25 had no lesions visible on MRI.
In general, the inflammatory lesions appeared hypointense on T1 and hyperintense on T2 sequences. The use of gadolinium contrast material increased the sensitivity of MRI with inflammatory lesions in the first article and had a predictive value of 74 percent for neoplasia in the second article.
Follow-up MRI studies are not often performed in veterinary medicine because of the expense and the owners' concerns regarding the anesthesia. It would be of diagnostic value to perform follow-up MRI examinations after certain treatments, tracking the size, intensity and enhancement of the lesion(s).
As a summary, MRI is important but not the only diagnostic procedure that should be performed in a patient with intracranial disease. It is important for the clinician to explain to the owner the significance of other neurological diagnostic tests and the limitations of the MRI.
Dr. Nanai is a resident of the European College of Veterinary Neurology/Neurosurgery at the Animal Emergency and Referral Center in Fort Pierce, Fla.
Dr. Lyman is a graduate of The Ohio State University College of Veterinary Medicine. He completed a formal internship at the Animal Medical Center in New York City. Lyman is a co-author of chapters in the 2000 editions of Kirk's Current Veterinary Therapy XIII and Quick Reference to Veterinary Medicine.