Hemifacial spasm associated with an intracranial mass in two dogs

Two dogs were presented with hemifacial spasm. Computed tomography images of both the dogs revealed an intracranial mass. In the first dog, a lesion at the level of the medulla oblongata was thought to cause primary irritation of the facial nucleus, with consequently permanent contraction of the ipsilateral facial muscles. In the second dog, a mass seemingly arising from the middle cranial fossa presumably isolated the facial motor neurons from upper motor neuron control, which resulted in hemifacial spasm as a result of loss of inhibitory interneuronal activity.