Sensitivity and specificity of MRI for detecting facial nerve abnormalities in dogs with facial neuropathy.

Idiopathic facial neuropathy in dogs is conventionally diagnosed by exclusion of structural and metabolic causes of a single cranial neuropathy. To investigate the reliability and validity of MRI for supporting a diagnosis of facial neuropathy in dogs, we examined MR images of the brainstem from 20 dogs with presumed idiopathic facial neuropathy, and 20 control dogs. Two different types of MRI sequence were compared: volumetric interpolated breath-hold examination MRI (VIBE-MRI), and conventional T1-weighted MRI. Three independent observers, blinded to the case details, were presented with VIBE-MR images in a random order, and were required to indicate the presence of hyperintensity of the facial nerve following intravenous contrast administration. The vestibulocochlear nerve was also assessed, and the whole process was repeated for conventional post-contrast T1-weighted images. Following contrast administration, the sensitivity of VIBE-MRI for detecting facial nerve abnormalities ranged from 86 per cent to 96 per cent, and the specificity from 87 per cent to 92 per cent; conventional T1-weighted images yielded a sensitivity of only 39 per cent - 65 per cent, and a specificity of 94 per cent - 96 per cent. MRI was not a sensitive detector of vestibulocochlear nerve abnormalities in 14 dogs with concurrent vestibular dysfunction. This study shows that VIBE-MRI is a robust technique for confirming presumed idiopathic facial neuropathy in dogs, and suggests an inflammatory component to this condition in a high proportion of dogs.