Magnetic resonance imaging of acquired trigeminal nerve disorders in six dogs.

The medical records and magnetic resonance (MR) images of dogs with an acquired trigeminal nerve disorder were reviewed retrospectively. Trigeminal nerve dysfunction was present in six dogs with histologic confirmation of etiology. A histopathologic diagnosis of neuritis (n=2) or nerve sheath tumor (n=4) was made. Dogs with trigeminal neuritis had diffuse enlargement of the nerve without a mass lesion. These nerves were isointense to brain parenchyma on T1-weighted (T1W) precontrast images and proton-density-weighted (PDW) images and either isointense or hyperintense on T2-weighted (T2W) images. Dogs with a nerve sheath tumor had a solitary or lobulated mass with displacement of adjacent neuropil. Nerve sheath tumors were isointense to the brain parenchyma on T1W, T2W, and PDW images. All trigeminal nerve lesions enhanced following contrast medium administration. Atrophy of the temporalis and masseter muscles, with a characteristic increase in signal intensity on T1W images, were present in all dogs.