haemifacial spasmnoun [ C ]
UK specialized US hemifacial spasm uk/hiː.mɪˌfeɪ.ʃəl ˈspæz.əm/us/ˈhiː.məˌfeɪ.ʃəl ˈspæz.əm/a spasm (= occasion when a muscle suddenly becomes tighter) affecting one side of the face:
Haemifacial spasms are caused by a blood vessel pressing on one of the nerves coming from the brain.