Hemifacial Spasm

If half of your face has started twitching on its own — first around the eye, then creeping down to the cheek and mouth — it's unsettling. Hemifacial spasm is almost always caused by a tiny blood vessel pressing on the facial nerve where it leaves the brainstem, and it's one of the few movement disorders we can cure with surgery.

What Is Hemifacial Spasm?

Hemifacial spasm is a condition in which the muscles on one side of your face start contracting on their own — without warning, without your control. It usually begins as a subtle flutter around the eye, and over months to years spreads downward to the cheek, corner of the mouth, and sometimes the neck.

The cause is almost always the same: a small blood vessel pulsing against the facial nerve (cranial nerve VII) at the root exit zone where it leaves the brainstem. Each pulse slowly wears away the nerve's insulation, causing the facial muscles to fire when they shouldn't. Population studies estimate ~11 cases per 100,000 people.

At a Glance

Hemifacial spasm is involuntary twitching of the muscles on one side of your face — it is not a tic or a stroke
The cause is almost always a small artery (usually the AICA) pressing on the facial nerve where it exits the brainstem
Botulinum toxin injections quiet the twitching for 3-4 months at a time but do not fix the underlying compression
Microvascular decompression surgery cures about 90% of patients and is the only treatment that addresses the root cause
Experienced centers use intraoperative hearing and nerve monitoring to keep complication rates very low

Symptoms

Early Symptoms

Intermittent twitching of the lower eyelid on one side — often mistaken for fatigue or caffeine
Brief, involuntary closure of the eye on the affected side

As It Progresses

Spasms spread downward to the cheek, corner of the mouth, and chin
Twitching that continues during sleep (distinguishes from simple tic)
Fatigue, bright light, reading, and stress often make it worse
A clicking sound in the ear on the affected side (from stapedius muscle contraction)
Mild weakness of the face between spasms in long-standing cases

Hemifacial spasm is almost always one-sided. If both sides twitch, the diagnosis is probably something else (blepharospasm, facial tic disorder, or movement disorder).

Diagnosis

High-Resolution MRI of the Brainstem

Dedicated thin-slice sequences (CISS or FIESTA) combined with MR angiography. Shows the facial nerve exiting the brainstem and the specific artery pressing on it — usually the AICA. Also rules out tumors, AVMs, or MS.

Electromyography (EMG) and the Lateral Spread Response

In hemifacial spasm, stimulating one branch of the facial nerve produces an abnormal 'spread' to muscles supplied by a different branch (lateral spread response, or LSR). This is highly specific to hemifacial spasm and is also used during surgery.

Ruling Out Mimics

Blepharospasm, facial tics, focal dystonia, post-facial-palsy synkinesis, and psychogenic facial movements must be excluded.

Treatment

Botulinum Toxin — A Bridge, Not a Cure

Small injections of botulinum toxin type A (Botox, Dysport, Xeomin) quiet the spasms for roughly 3-4 months at a time. Works in ~85-95% of patients. Side effects include temporary lid droop, weakness of the corner of the mouth, dry eye. The underlying nerve compression continues and the nerve continues to deteriorate.

Microvascular Decompression (MVD) — The Curative Operation

Pioneered by Peter Jannetta at University of Pittsburgh; his 1995 series of 782 operations established it as a safe, definitive cure. Procedure: a silver-dollar-sized opening behind the ear (retromastoid craniotomy); surgeon works along the cerebellum to reach the facial nerve at the brainstem; offending artery (usually AICA) carefully mobilized off the nerve; small piece of shredded Teflon felt tucked between vessel and nerve; bone and scalp closed. Most patients home in 2-3 days.

Intraoperative Monitoring

Two critical signals: (1) Brainstem auditory evoked responses (BAER) — warns of hearing danger before loss occurs. (2) Lateral spread response (LSR) — disappears in real time when the offending vessel is successfully lifted off the nerve, providing 'cure confirmed' feedback.

Stereotactic Radiosurgery: NOT Recommended for HFS

Unlike trigeminal neuralgia, hemifacial spasm is not a good target for Gamma Knife. Carries meaningful risk of facial weakness.

Outcomes

Outcome	Rate	What to Know
Complete cure (spasm freedom)	~90%	Meta-analysis of 6,249 patients; 84% excellent results at 10 years in Jannetta series
Delayed resolution	up to ~30%	Some patients take weeks to months to become spasm-free
Long-term recurrence	~1-2%	Nearly all failures occur within 24 months
Hearing preservation	~97-99%	Modern series with BAER monitoring; permanent hearing loss 1-3%
Permanent facial weakness	~1%	Transient weakness more common and usually recovers fully
CSF leak / serious complications	1-3%	Stroke, infection, and operative mortality all well under 1%

If you're spasm-free at two years, you are very likely spasm-free for life.

References

Barker FG 2nd, Jannetta PJ, et al. Microvascular decompression for hemifacial spasm. J Neurosurg. 1995;82(2):201-210. PMID: 7815147
Holste K, et al. Spasm freedom following MVD for hemifacial spasm: systematic review and meta-analysis. World Neurosurg. 2020;139:e383-e390. PMID: 32305605
Jung NY, et al. Hearing outcome following MVD for hemifacial spasm: series of 1434 cases. World Neurosurg. 2017;108:566-571. PMID: 28927910
Moller AR, Jannetta PJ. Monitoring facial EMG responses during MVD for hemifacial spasm. J Neurosurg. 1987;66(5):681-685. PMID: 3572493
Sindou M, Mercier P. Microvascular decompression for hemifacial spasm: outcome on spasm and complications. Neurochirurgie. 2018;64(2):106-116. PMID: 29454467
Yaltho TC, Jankovic J. The many faces of hemifacial spasm: differential diagnosis. Mov Disord. 2011;26(9):1582-1592. PMID: 21469208

Our Specialists

Peter Warnke, MD

Neurosurgery

Peleg Horowitz, MD, PhD

Neurosurgery

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