Hemifacial spasm is an uncommon disorder where patients experience frequent, involuntary contractions, or spasms, on one side of their face. It is typically caused by a blood vessel pulsating at the origin of the facial nerve from the brainstem.
The facial nerve is the 7th of 12 cranial nerves. It arises from the brainstem and passes into the temporal bone, where it splits into five main branches. The facial nerve has a complex and broad range of functions but primarily serves to control the muscles of facial expression.
Hemifacial spasm typically starts as spasmodic, irregular contractions of the eyelids. Over time, it gradually progresses to involving the entire side of the face, including the mouth. Infrequently, the contractions will start in the mouth and spread to the eye.
The repeated pulsing of the blood vessel on the facial nerve is thought to damage the nerve and cause increased neural excitability, leading to the contractions of the facial muscles. Occasionally, hemifacial spasm may be caused by a tumor or vascular malformation creating pressure on the facial nerve. In rare instances, no cause may be found.
The typical workup for hemifacial spasm involves obtaining a special MRI through the brainstem, looking for a branch of a blood vessel, tumor, or vascular malformation. If a tumor or vascular malformation is identified, then appropriate treatment may involve surgery or endovascular treatment (the treatment of a vascular lesion using minimally invasive techniques through the groin). If a blood vessel is identified as the cause, the primary treatment is either Botulinum Toxin (Botox) or surgical decompression of the nerve. Treatment of hemifacial spasm with Botox involves the injection of the toxin in the face. Treatment is often successful but requires repeated office procedures every few months.
The surgical procedure is known as a Microvascular Decompression. It involves gently identifying the nerve and carefully dissecting away the offending vessel. A small piece of felt or Teflon is placed to prevent the vessel from returning to its prior position. Surgery has been reported to be successful approximately 80% of the time.