Hemifacial spasm (HFS) is considered to be a form of segmental myoclonus of muscles innervated by the facial nerve (CN VII), with unilateral twitching beginning in the orbicularis oculi, and spreading to the other ipsilateral muscles of facial expression over several years. Over time, patients may present with sustained or tonic contractions.Reference Lu, Yeung, Gerrard, Michaelides, Sekula and Bulsara ¹ The prevalence of HFS is 14.5 per 100,000 women and 7.4 per 100,000 men, with an average age of onset of 44 years.Reference Lu, Yeung, Gerrard, Michaelides, Sekula and Bulsara ^{1 ,} Reference Chaudhry, Srivastava and Joshi ² Primary HFS is triggered by vascular compression whereas secondary HFS comprises all other causes of CN VII damage, thus, magnetic resonance imaging is recommended in all patients with HFS.Reference Glocker, Krauss, Deuschl, Seeger and Lucking ³ Primary HFS most commonly occurs secondary to arterial compression of the CN VII at the root exit zone (REZ).Reference Campos-Benitez and Kaufmann ⁴ Venous compression is rare.Reference Campos-Benitez and Kaufmann ^{4 -} Reference Jannetta ⁶ Secondary causes include brainstem tumours, stroke, demyelinating plaques, trauma or Bell’s palsy.Reference Campos-Benitez and Kaufmann ⁴ We describe a rare case of HFS associated with a pontine developmental venous anomaly (DVA).

A 32 year-old otherwise healthy woman presented with left HFS since the age of five years. The spontaneous twitching initially involved the left eye; subsequently progressing to become tonic spasms of the left face and anterior neck over several years. These were exacerbated by voluntary facial movements and stress; eventually increasing in frequency and persisting for a longer duration, lasting over one minute (Video 1). There were no speech changes, ocular deviation or other abnormal movements. The remainder of her neurological examination was normal. Electroencephalogram (EEG) was normal. Magnetic resonance imaging brain showed a DVA in the left pons in proximity to the left CN VII REZ (Figure 1). Carbamazepine and phenytoin were tried, but discontinued early due to adverse reactions (flu-like illness and vomiting, respectively). She responded to botulinum toxin (onabotulinumtoxinA) injections in the affected left facial muscles.

Figure 1 Two selected images from axial post-contrast 3D T1 MRI sequence acquisition show a tuft of tributary veins, or “caput medusae” (A, arrow), consistent with a developmental venous anomalyReference Ruíz, Yilmaz and Gailloud ¹⁴ , in the left posterior pons near the fourth ventricle leading to the larger draining abnormal vein (B, arrowhead) which is seen apposed to the left 7th cranial nerve in its root exit zone in the cerebellopontine angle cistern. There was no infarction, hemorrhage, mass or other relevant finding on the study.

Hemifacial spasm is thought to result from hyperexcitability of the CN VII nucleus due to antidromic feedback from peripheral lesions compressing the nerve or ephaptic transmission within the proximal segment of CN VII, leading to excessive firing.Reference Chaudhry, Srivastava and Joshi ² Hemifacial spasm is most commonly caused by vascular compression of CN VII by the anterior inferior cerebellar artery (43%), posterior inferior cerebellar artery (31%), vertebral artery (23%), or a large vein (3%).Reference Campos-Benitez and Kaufmann ^{4 ,} Reference Wang, Thirumala and Shah ⁵ Untreated, HFS can lead to social embarrassment and, in severe cases, involuntary eye closure may interfere with vision.Reference Chaudhry, Srivastava and Joshi ² The prognosis depends on treatment selection and response. Anticonvulsants, such as carbamazepine, may be tried with variable efficacy (level U) and limited by side effects, such as sleepiness, headaches, dizziness and ataxia.Reference Chaudhry, Srivastava and Joshi ² The response to anticonvulsants in certain cases of HFS may suggest another pathophysiological mechanism.

Microvascular decompression (MVD) has been shown to be effective in 84-98% of primary HFS patients (level C)Reference Campos-Benitez and Kaufmann ^{4 ,} Reference Zhu, Li and Zhong ⁷ ; with delayed response in 25.4%Reference Xia, Zhong, Zhu, Dou, Liu and Li ⁸ , sometimes taking up to three years for resolution of symptoms.Reference Jo, Kong and Park ⁹ Recurrence may develop in 10.3% of patients within two years.Reference Zhu, Li and Zhong ⁷ Causes of failed MVD may be related to missing the offending vessel, not detaching all offending vessels, or related to a difficult surgical approach.Reference Zhong, Li and Zhu ¹⁰ Intraoperative electromyography monitoring over the mentalis, looking for the reduction or elimination of the abnormal muscle response may help increase the success of MVD.Reference Zhu, Li and Zhong ⁷ Although repeat MVD may be required with good reported successReference Xia, Zhong, Zhu, Dou, Liu and Li ⁸ , this puts patients again at risk of surgical complications, including hearing loss, facial palsy, ataxia, cerebrospinal fluid leakage, diplopia, headache, wound infection, and vertigo.Reference Miller and Miller ^{11 ,} Reference Wang, Thirumala and Shah ¹² Due to these surgical risks, delayed response, and occasional difficulty in identifying a culprit vessel, botulinum toxin may be used as first line for HFS. Microvascular decompression may be performed after failed treatment with botulinum toxin.Reference Miller and Miller ^{11 ,} Reference Wang, Thirumala and Shah ¹²

A recent study of 15 patients (mean 52.8 years) suggests that patients with HFS associated with venous compression show a higher incidence of neck (platysma muscle) involvement and tonic contraction (tonus) of the facial musclesReference Wang, Thirumala and Shah ⁵ , as seen in our patient. Infratentorial veins may be the primary or secondary offending vessel in HFS. Female sex and venous involvement have been associated with recurrence of HFS after MVD.Reference Wang, Thirumala and Shah ⁵ This may be related to location or severity of compression.

There are very few cases of HFS due to DVA reported in the literature (Table 1). Developmental venous anomalies, also known as venous angiomas, are congenital benign anatomic variants which account for over 60% of cerebral vascular malformations; with very low risk for bleeding or for causing symptoms, unless associated with a cavernous malformation.Reference Chiaramonte, Bonfiglio, Amore and Chiaramonte ¹³ Typically, neurosurgical manipulation of DVAs is generally avoided, due to their relatively benign nature and vital role in drainage of normal brain tissue, fragility and risk of venous infarction from manipulation.Reference Ruíz, Yilmaz and Gailloud ^{14 ,} Reference Chen, Lee and Lui ¹⁵ There is minimal literature on MVD for DVAs associated with HFS, with resolution of HFS symptoms in twoReference Chen, Lee and Lui ^{15 ,} Reference Mahran, Samii, Penkert and Ostertag ¹⁶ of the three reported cases; without long-term post-operative followup.Reference Chen, Lee and Lui ^{15 -} Reference Arita, Kishima and Hosomi ¹⁷ Botulinum toxin is thus a reasonable option for symptomatic treatment of HFS associated with isolated DVA, as selected for our patient.

Table 1 Reported cases in the literature of HFS associated with DVA.

CBZ: carbamazepine; DVA: developmental venous anomaly; F: female; HFS: hemifacial spasm; M: male; CN: cranial nerve; REZ: root exit zone; IAC: internal auditory canal.

Of the commercially available formulations of botulinum toxin in Canada, evidence supports a level B recommendation for onabotulinumtoxinA, and a level U recommendation for incobotulinumtoxinA for the symptomatic treatment of HFS.Reference Hallett, Albanese and Dressler ¹⁸ The latency of improvement after botulinum toxin injections in HFS is between 2-14 days, with mean duration of improvement of 15.7 weeks, and 85% improvement in spasms, as reported by patients.Reference Sorgun, Yilmaz, Akin, Mercan and Akbostanci ¹⁹ Side effects are transient and most commonly include mild ptosis (mean: 24%) and facial weakness (mean: 27%).Reference Sorgun, Yilmaz, Akin, Mercan and Akbostanci ¹⁹

Our patient is the youngest reported case of HFS associated with isolated pontine DVA with symptoms presenting in childhood. Because the complication rate and recurrence risk is high for MVD of veins associated with HFS, botulinum toxin may be a reasonable treatment to offer such patients.

P Rizek, N Kumar, and M Sharma report no disclosures relevant to manuscript. M Jog has received consulting fees as an advisor for Abbvie Canada, Allergan and Merz Pharma Canada. He has obtained research support from Merz, Allergan, CIHR, Mitacs, AMOSO and the Age-Well Network of Centers of Excellence (NCE) of Canada program.

Statement of Authorship

P Rizek – Study concept, design, writing of the first draft and revision of the manuscript. N Kumar – Study concept and design. M Sharma – Selection of imaging and interpretation. M Jog – Study supervision, revision and critique of the manuscript.