Saint John's Health Center
Hemifacial Spasm

Overview 

The facial nerve (cranial nerve VII or 7th nerve) is responsible for controlling movement of the face. Hemifacial spasm is a syndrome of recurring facial muscle twitches and spasms that can occur when the facial nerve is irritated or compressed by a blood vessel that courses along the brainstem.  

The facial nerve is intimately related to the acoustic nerve (VIII-8th) which is responsible for hearing and balance; they both emerge from the brainstem in close proximity and share a confined space before entering the bone into the inner ear through a common opening called the internal auditory canal.

Figure 1:  The close relationship of the facial (VII) and acoustic (VIII) nerve are demonstrated.  The two are shown here separated by a black line, but in reality they are superimposed one on top of the other. Compression of the facial nerve most often occurs directly at the level of the brainstem where it emerges into the fluid space.  The nerve is located underneath the hearing and balance nerve making access particularly challenging.  The blood vessel causing the compression maybe small and even a vein maybe responsible.

Hemifacial Spasm Pic1 

Figure 2: A small artery is seen (circled area) causing compression of the facial nerve (VII) at the origin of the brainstem. It is postulated that the compression creates stimulation of the nerve in a reverse direction (retrograde transmission).  This results in formation going backwards into the origin of the nerve (Facial nucleus). The nerve unable to process the unusual stimulation responds by firing creating uncontrolled facial twitching. 

 

Hemifacial Spasm Pic2 

Diagnosis  

The development of the symptomatic twitching is generally predictable. It initially starts in the eye lid occurring primarily with activity and movement. Eventually the twitching marches down the face through the cheek, jaw and into the neck. The twitching becomes uncontrolled and occurs even when the patient is trying to quietly rest the face. In more severe cases the twitching progresses to sustained facial contractures referred to as “tonus phenomena”. Tonus phenomena behaves like a “Charlie horse of the face” creating periods where the face becomes locking in place with eyes closed, cheeked contracted and jaw clenched. In addition to being painful this can be dangerous as it creates uncontrolled loss of binocular vision by closing one eye. These situations can lead to sudden and unpredictable loss of depth perception and 3-dimensional vision.

Treatment 

Treatment for Hemifacial Spasm can also be divided into the 3 general categories discussed for Trigeminal Neuralgia: Medical Therapy, Ablative Therapy, and Microvascular Decompression.
Medical Therapy: Several medications have been attempted to treat Hemifacial spasm with little consistent success. Most commonly these drugs fall into the general category of muscle relaxants or sedatives. Unlike trigeminal neuralgia, Hemifacial Spasm is rarely responsive to medication on a consistent basis.
Ablative Therapy: Botox therapy has been used to create a functional chemical block between the fine nerve endings of the facial nerve and their insertion into the muscles of the face. The Botox is applied to the muscles by a series of injections. Over time the Botox has a potential of reduced efficacy requiring more frequent injections to provide ongoing control. Often this will require injections at 9, 6, then 3-month intervals. The effects of Botox may potentially create facial weakness overtime.
Microvascular Decompression: Over 90% of patients benefit from significant relief of their HFS following an MVD.  The operation is well tolerated, but has associated risks.  The risk of hearing loss (on the side of the operation) can range from 1-6%. Careful measures are taken during surgery to minimize these risks..
 
 
  

Microvascular Decompression:  

This procedure is intended to move the offending vessel off the nerve by creating a cushion or pad between the facial nerve and offending blood vessel.   It addresses the root cause of Hemifacial Spasm by dealing with vessel causing the compression.  The surgery involves a keyhole retromastoid craniotomy made through a small incision behind the ear. Through this opening and using a high-definition endoscope or microscope, small pads of Teflon are placed between the nerve and vessel to “decompress” the nerve and allow it to function normally. Using this technique, there is little or no need for brain retraction or nerve manipulation.   

Figure 3: A small keyhole craniotomy (shadowed circle) is created behind the ear and a path (arrow) using the space created by the drainage of the CSF is used to access the facial nerve and compressing artery.  The artery is carefully mobilized using a microscope,endoscope or combination of both. Small pieces of Teflon (white circles) are placed to keep the vessel away from the nerve. 

Hemifacial Spasm Pic1