Exclusion of a Brain Lesion: Is Intravenous Contrast Administration Required after Normal Precontrast Magnetic Resonance Imaging?

BACKGROUND: No evidence‐based guidelines are available for the administration of gadolinium‐based contrast media to veterinary patients. OBJECTIVE: To investigate whether administration of intravenous (IV) contrast media alters the likelihood of identifying a brain lesion in dogs and cats. ANIMALS: Four hundred and eighty‐seven client‐owned animals referred for investigation of intracranial disease. METHODS: Two reviewers retrospectively analyzed precontrast transverse and sagittal T1‐weighted (T1W), T2‐weighted, and fluid‐attenuated inversion recovery low‐field MRI sequences from each patient for the presence of a clinically relevant brain lesion. All sequences subsequently were reviewed in the same manner with additional access to postcontrast T1W images. RESULTS: Of the 487 precontrast MRI studies, 312 were judged to be normal by 1 or both reviewers. Of these 312 studies, a previously undetected lesion was identified in only 6 cases (1.9%) based on changes observed on postcontrast sequences. Final diagnoses included meningoencephalitis of unknown origin (n = 1), feline infectious peritonitis (n = 1), and neoplasia (n = 2). All 4 of these cases had persistent neurological deficits suggestive of an underlying brain lesion. Contrast enhancement observed in the 2 other cases was considered falsely positive based on the results of further investigations. CONCLUSIONS AND CLINICAL IMPORTANCE: In patients with normal neurological examination and normal precontrast MRI, the subsequent administration of IV gadolinium‐based contrast media is highly unlikely to disclose a previously unidentified lesion, calling into question the routine administration of contrast media to these patients. However, administration still should be considered in animals with persistent neurological deficits suggestive of an underlying inflammatory or neoplastic brain lesion.