Surgical Management of Hemifacial Spasm and Meige Syndrome

Introduction

Hemifacial spasm (HFS) is a unilateral, involuntary, paroxysmal movement of facial muscles innervated by the ipsilateral facial nerve. Its characteristic features include tonic–clonic contractions and synkinesis of the muscles. These symptoms usually start from the orbicularis oculi muscle and gradually spread inferiorly to the muscles around the cheek, mouth, and neck. Eventually the facial spasm worsens in frequency and severity, resulting in sustained muscle contractions and a disfiguring grimace ( ).

In Schultze first reported the concept of vascular compression in a 56-year-old man with left HFS, revealing at autopsy a giant aneurysm from the left vertebral artery that was compressing the facial nerve root. Gowers described the classical clinical features of HFS in , and the terminology of “Hémispasme facial périphérique” was initially used by Babinski in . Gardner reported his first case of HFS treated by posterior fossa vascular decompression surgery in . In the 1970s Jannetta expanded Gardner’s neurovascular compression theory and established the microvascular decompression (MVD) procedure as a standard treatment for HFS ( ). Since then detailed surgical techniques for MVD have advanced, with the development of neuroimaging and intraoperative monitoring in the pursuit of better outcomes and fewer complications ( ).

Clinical Diagnosis

The diagnosis of HFS is made based on the clinical symptoms. Synchronized upper facial muscle contractions are the main feature of HFS diagnosis and are induced by a simple physical maneuver, like lifting the ipsilateral eyebrow with eye closure (the other Babinski sign) ( ). Furthermore, HFS mimics other craniofacial dyskinesias, including blepharospasm, tics, synkinesis, myokymia, craniocervical dystonia, and partial seizures ( ). Psychogenic HFS is rare, occurring in 2.4% of patients, who do not require surgical treatment ( ). It is very important to differentiate HFS from other similar diseases ( ).

• Blepharospasm is characterized by bilateral synchronous contractions of the muscles around the eye. It differs from HFS in being bilateral, and involves only the musculature around the eye rather than presenting with steady progression down the face, as in HFS.

• Tics are brief, repetitive, stereotyped, and involuntary movements. Tics are similar to the movements of habitual spasms like blinking, and are associated with more tonic components than HFS.

• Facial myokymia is characterized by unilateral, undulating, worm-like, continuous muscle contractions associated with intrinsic brainstem pathology, which has a distinct and diagnostic electromyographic pattern. The symptoms disappear spontaneously in most cases within a few weeks.

• Postparalytic synkinesis may occur after aberrant regeneration of the facial nerve following Bell’s palsy. A history of antecedent Bell’s palsy, with these movements developing on regeneration of the nerve, is helpful in differentiating this condition.

• Tardive dyskinesia is associated with a history of exposure to dopaminergic antagonists or other neuroleptic drugs. It usually presents as stereotypical movements of the face, especially around the lips and neck.

Neuroradiologic Evaluations

Neuroradiologic examinations are usually required to confirm the diagnosis and detect the cause of HFS. In most patients the pathogenesis of HFS is attributed to neurovascular compression of the facial nerve at the root exit zone; however, a minority of patients with HFS may have secondary causes like a space-occupying lesion or demyelination, which must be ruled out ( ). Of the various modalities, high-resolution three-dimensional (3D) T2-weighted sequences of magnetic resonance imaging (MRI), including 3D balanced steady-state free precession (SSFP) imaging such as constructive interference in the steady state (CISS) or fast imaging employing steady-state acquisition, are useful to assess the location of the neurovascular compression ( ). These are imaging methods combined with fast-gradient echo that have various advantages, such as a high signal-to-noise ratio, high spatial resolution, and less cerebrospinal fluid (CSF) flow artifact ( ). Three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) can assist in evaluation of the anatomical characteristics of the vascular structures at the root exit zone ( ) ( Fig. 78.1 ), and 3D SSFP and TOF MRA have a high accuracy in detecting the offending vessels compressing the facial nerve ( ). Fusion imaging of 3D magnetic resonance cisternograms and angiograms is also useful for the preoperative assessment for MVD in patients with HFS to show the relationship between the vessel and nonvascular soft tissues clearly ( ). Three-dimensional virtual endoscopy not only provides excellent views of the neurovascular structure but also enables preoperative simulations of the surgery ( ). Recently, with the development of imaging techniques and software, 3D tubular models make it possible to understand preoperative 3D neurovascular structures at a level that nearly matches the intraoperative findings ( ).

In addition, 3D TOF MRA can describe the postoperative state of the decompression site between the vessels and the root exit zone. These findings may be helpful to guide further management in patients with persistent or recurrent HFS after MVD ( ). In our institution we routinely use 3D TOF MRA and CISS imaging for the preoperative evaluation of patients with HFS, and if needed these images are acquired to ascertain whether adequate decompression was performed in failure cases ( Fig. 78.2 ).

Additional Methods

Electromyography (EMG) can differentiate HFS from other abnormal movement disorders with a muscle or denervation origin. Electrophysiological findings such as detecting lateral spread are an important hallmark providing additional information to make a diagnosis and determine whether adequate decompression has been achieved during surgery. Preoperative audiologic examinations including pure tone audiometry and tympanometry are informative to make a decision on surgery. If a patient has a hearing impairment on the contralateral side of the HFS, risking hearing loss, the surgeon has to contemplate performing the MVD or make a vigilant preoperative plan. Detailed information is given below in the subsection on intraoperative monitoring.