statdx/docs_md/articles/hemifacial-spasm_1b390143-1212-4447-beb3-ed9e85ef34e4.md

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Hemifacial Spasm	1b390143-1212-4447-beb3-ed9e85ef34e4	key value eef2f839-5706-47b9-89c3-60d8315b2b3a Nicholas A. Koontz, MD	name slug treeNodeId Head and Neck head-and-neck ed24ed8c-5d57-4629-879b-447b82d2973d name slug treeNodeId Differential Diagnosis differential-diagnosis 40d68862-8975-4dde-ac2b-ebc43ab0fb5c name slug treeNodeId CPA-IAC and Posterior Fossa cpa-iac-and-posterior-fossa c590eedb-4a3b-4158-a04f-ad880564c992 name slug treeNodeId Clinically Based Differentials clinically-based-differentials 55dd15ac-e67d-48dd-8134-f52884dab28b name slug treeNodeId Hemifacial Spasm hemifacial-spasm null	Head and Neck	959076b8-9c94-4244-89b0-0721f3a2387b	23	08/15/18	Hemifacial Spasm	Head and Neck, Differential Diagnosis, CPA-IAC and Posterior Fossa, Clinically Based Differentials, Hemifacial Spasm	Hemifacial Spasm | STATdx	Hemifacial Spasm	DDX	true	Head and Neck Differential Diagnosis CPA-IAC and Posterior Fossa Clinically Based Differentials Hemifacial Spasm

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title: "Hemifacial Spasm" docid: "1b390143-1212-4447-beb3-ed9e85ef34e4" authors:

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ESSENTIAL INFORMATION

• Key Differential Diagnosis Issues

  • Overall statistics - In > 95% of cases, arterial vascular loop is cause of hemifacial spasm (HFS) - All other causes listed account for < 5% of cases
  • HFS - Definition: Segmental myoclonus of muscles of face innervated by facial nerve - Presentation: Patients 50-80 years old, unilateral - Begins around eye, spreads gradually to other facial muscles - Principal symptom: Rhythmic, involuntary, myoclonic facial muscle contractions - Pathophysiology: Irritation of facial nerve or facial nucleus
  • Vascular loop syndrome affecting CNVII (aka pimary HFS) - By far most common cause of HFS - Aberrant or ectatic vessels in cistern - Anterior inferior cerebellar artery (AICA) most common offending artery (40-50%) - Other less common causal vessels include posterior inferior cerebellar artery (PICA) (~ 30%), vertebral artery (VA) (~ 20%), or large vein (< 5%) - Multivessel impingement is frequent (~ 40%) - High-resolution MR-MRA routinely identifies compressive aberrant or ectatic arteries - T2 SPACE, CISS, or FIESTA sequences most commonly employed - Critical to recognize that vascular contact of facial nerve is very common (~ 50% of population) with only tiny minority (< 0.01 %) manifesting HFS - In absence of HFS symptoms, this is incidental finding that should be ignored

• Helpful Clues for Common Diagnoses

  • Vascular Loop Syndrome Affecting CNVII - Negative high-resolution MR exam does not preclude surgery for smaller vascular loop causing HFS - High-resolution MR makes this situation far less common - Imaging findings - MR-MRA: Asymmetric looping artery impinges on CNVII in CPA - Root exit zone and attached segment (where CNVII is adherent to pons) are most sensitive to neurovascular compression - AICA > PICA > VA > venous, though all are possible culprits

• Helpful Clues for Less Common Diagnoses

  • Epidermoid Cyst in CPA - Morphology: Assumes shape of cistern it occupies - Insinuating margins, encasing cranial nerves and vessels - Imaging findings - Near CSF signal intensity of epidermoid cyst makes it difficult to see on T1, T2, and FLAIR sequences - DWI shows reduced diffusivity
  • Meningioma in CPA - Morphology: Dural-based sessile mass - Imaging findings - Bone CT: Bony hyperostosis possible - MR: Enhancing mass with dural tail(s)
  • Aneurysm in CPA**-IAC** - Morphology: Ovoid or fusiform shape - Imaging findings - MR: Complex lesion signal from wall calcification, clot, and flow
  • Facial Nerve Schwannoma in CPA-IAC - Morphology: CPA-IAC "ice cream on cone" mass and labyrinthine segment tail - Imaging findings - Bone CT: Labyrinthine segment CNVII enlarged - MR: Enhancing tubular mass with tail; may have intramural cysts
  • Facial Nerve Schwannoma in T-Bone - Morphology: Tubular mass within enlarged facial nerve canal may pedunculate into middle ear cavity (tympanic segment CNVII) or mastoid air cells (mastoid segment CNVII) - Imaging findings - Bone CT: Obvious enlargement of CNVII canal; geniculate ganglion most commonly affected - MR: Enhancing mass enlarges bony facial nerve canal
  • Facial Nerve Perineural Tumor - Morphology: Enlargement of intratemporal CNVII connected through stylomastoid foramen (usually from invasive parotid malignancy) - Imaging findings - Mastoid segment most common - CT: Soft tissue replacement of fat at stylomastoid foramen ± enlargement of bony CNVII canal - MR: Enhancing minimally enlarged intratemporal CNVII
  • Facial Nerve Venous Malformation ("Hemangioma") in T-Bone - Lesion of abnormal vascular morphogenesis; thus "hemangioma" is misnomer - Morphology: Amorphous geniculate ganglion area mass - Imaging findings - Bone CT: "Honeycomb" bone matrix (50%) - MR: Avidly enhancing mass with foci of low signal intensity and gradient susceptibility (calcifications)

• Helpful Clues for Rare Diagnoses

  • AcuteCerebral Ischemia-Infarction - Acute onset of brainstem-related symptoms - Pontine CVA secondary to basilar artery perforator injury - Imaging findings - MR: DWI shows reduced diffusivity in pons
  • Multiple Sclerosis - HFS is rare presentation of multiple sclerosis - Imaging findings - Plaques in vicinity of facial nerve nucleus in floor of 4th ventricle may or may not be seen - MR: T2/FLAIR show ↑ signal intensity of supratentorial white matter plaques
  • Arteriovenous Malformation - More commonly supratentorial - Imaging findings - MR: Large ectatic arterial flow voids - Enhancing nidus on T1 C+ fat-saturated sequence - Large draining veins
  • Arachnoid Cyst in CPA - More common than epidermoid cyst in CPA, but epidermoid cyst in CPA more often associated with HFS - Morphology - Fills cistern with rounded or flat margins - Imaging findings - T1 C+: No enhancement - FLAIR: Follows dark CSF signal intensity - DWI: No reduced diffusivity
  • Venous Malformation ("Hemangioma") in IAC - Lesion of abnormal vascular morphogenesis; thus "hemangioma" is misnomer - Morphology: Distal intracanalicular (IAC) ovoid to round cystic mass - Imaging findings - Bone CT: Lesion with punctate calcifications - MR: Avidly enhancing IAC lesion with foci of low signal intensity and gradient susceptibility (calcifications)

• Alternative Differential Approaches

  • Radiologist generally searches for cause of cranial neuropathy by following cranial nerve from origin to functional endplate - Such anatomic approach permits segmentation of potential causes into anatomic groups
  • Anatomic delineation of HFS causes - 3 general anatomic sites where facial nerve may be injured causing HFS - Intraaxial (nuclear) - Cisternal (CPA or IAC cistern) - Intratemporal (intratemporal facial nerve canal)
  • Intraaxial (nuclear) - Acute cerebral ischemia-infarction - Multiple sclerosis - Arteriovenous malformation
  • Cisternal (CPA or IAC cistern) - Vascular loop syndrome affecting CNVII - Epidermoid cyst in CPA - Meningioma in CPA - Aneurysm in CPA-IAC - Facial nerve schwannoma in CPA-IAC - Arachnoid cyst in CPA - Venous malformation ("hemangioma") in IAC
  • Intratemporal (intratemporal CNVII canal) - Facial nerve schwannoma in T-bone - Facial nerve perineural tumor - Facial nerve venous malformation ("hemangioma") in T-bone

References

Selected References

1. Donahue JH et al: Imaging of vascular compression syndromes. Radiol Clin North Am. 55(1):123-138, 2017
2. Deep NL et al: Magnetic resonance imaging assessment of vascular contact of the facial nerve in the asymptomatic patient. J Neurol Surg B Skull Base. 77(6):503-509, 2016
3. Haller S et al: Imaging of neurovascular compression syndromes: trigeminal neuralgia, hemifacial spasm, vestibular paroxysmia, and glossopharyngeal neuralgia. AJNR Am J Neuroradiol. 37(8):1384-92, 2016
4. Öcal R et al: Comparison of brain MRI angiography and brain MRI cisternography in patients with hemifacial spasm. Acta Neurol Belg. 116(4):593-598, 2016
5. Ray DK et al: Surgical outcome and improvement in quality of life after microvascular decompression for hemifacial spasms: a case series assessment using a validated disease-specific scale. Stereotact Funct Neurosurg. 88(6):383-9, 2010
6. Pyen JS et al: Tic convulsif caused by cerebellopontine angle schwannoma. Yonsei Med J. 2001 Apr;42(2):255-7. Retraction in: Yonsei Med J. 49(6):1060, 2008
7. Desai K et al: Cerebellopontine angle epidermoid tumor presenting with hemifacial spasms. Neurol India. 51(2):288-9, 2003
8. Iwai Y et al: Hemifacial spasm due to cerebellopontine angle meningiomas--two case reports. Neurol Med Chir (Tokyo). 41(2):87-9, 2001
9. Takano S et al: Facial spasm and paroxysmal tinnitus associated with an arachnoid cyst of the cerebellopontine angle--case report. Neurol Med Chir (Tokyo). 38(2):100-3, 1998
10. Illingworth RD et al: Hemifacial spasm: a prospective long-term follow up of 83 cases treated by microvascular decompression at two neurosurgical centres in the United Kingdom. J Neurol Neurosurg Psychiatry. 60(1):72-7, 1996
11. Moriuchi S et al: Hemifacial spasm due to compression of the facial nerve by vertebral artery-posterior inferior cerebellar artery aneurysm and elongated vertebral artery--case report. Neurol Med Chir (Tokyo). 36(12):884-7, 1996
12. Nagata S et al: Hemifacial spasm caused by CP angle AVM associated with ruptured aneurysm in the feeding artery--case report. Neurol Med Chir (Tokyo). 31(7):406-9, 1991

Images

Selected Images

Vascular Loop Syndrome Affecting CNVII Axial T2 FS MR in a patient with left hemifacial spasm (HFS) shows neurovascular compression of the left facial nerve by an ectatic vertebral artery . Note the point of neurovascular impingement against the adjacent cerebellar flocculus .

Vascular Loop Syndrome Affecting CNVII Axial T2 FS MR in a patient with left hemifacial spasm (HFS) shows neurovascular compression of the left facial nerve by an ectatic vertebral artery . Note the point of neurovascular impingement against the adjacent cerebellar flocculus .

Vascular Loop Syndrome Affecting CNVII Axial T2 FS MR in a patient with left hemifacial spasm (HFS) shows neurovascular compression of the left facial nerve by an ectatic vertebral artery . Note the point of neurovascular impingement against the adjacent cerebellar flocculus .

Vascular Loop Syndrome Affecting CNVII Coronal T2 MR shows an ectatic vertebral artery "lifting" the posterior inferior cerebellar artery into the root exit zone of the facial nerve . Note compression of the lateral pons.

Epidermoid Cyst in CPA Axial DWI MR in a patient with chronic left HFS shows a left CPA mass with reduced diffusivity and scalloped, insinuating margins, typical of an epidermoid cyst.

Meningioma in CPA Axial T1 C+ FS MR in a patient with right HFS shows an avidly enhancing mass with the configuration of "ice cream" (CPA component) "on cone" (IAC component) . Note enhancing dural tails , which help differentiate this histologically-proven CPA-IAC meningioma from a schwannoma.

Aneurysm in CPA-IAC Axial T2 FS MR shows a giant right vetebral artery aneurysm with complex signal intensity. The aneurysm obliterates the pontomedullary junction at the region of the right CNVII root exit zone . The same tortuous right vertebral artery also effaces the left CNVII root exit zone region.

Facial Nerve Schwannoma in CPA-IAC Axial SPGR C+ MR of left facial nerve schwannoma shows an avidly enhancing CPA-IAC mass with a labyrinthine tail of enhancement extending to the geniculate ganglion , which differentiates it from a vestibular schwannoma.

Facial Nerve Schwannoma in T-Bone Axial T1 C+ MR shows an aggressive schwannoma involving the tympanic segment , posterior genu , and descending mastoid segment of the right facial nerve. Note several nonenhancing intramural cysts .

Facial Nerve Perineural Tumor Coronal T1 MR shows invasive parotid space malignancy with perineural tumor spread cephalad through the stylomastoid foramen to involve the mastoid segment of the facial nerve .

Facial Nerve Venous Malformation ("Hemangioma") in T-Bone Axial T1 C+ FS MR shows an enhancing lesion within enlarged geniculate fossa. Note the black central dot of low signal intensity corresponding with punctate calcification and suggesting the diagnosis of facial nerve venous malformation.

Acute Cerebral Ischemia-Infarction Axial DWI MR shows an acute left pontine infarction with reduced diffusivity. Corresponding hypointensity was present on the ADC map (not shown). Patients with brainstem infarctions may develop hemifacial spasm in the subacute to chronic phase.

Multiple Sclerosis Axial T2 FS MR in patient with multiple sclerosis shows a subtle demyelinating plaque in the left lateral pons near the root exit zone of the facial nerve . Demyelinating lesions accounting for HFS are often subtle and may not always be seen.

Arteriovenous Malformation Axial T2 MR shows a left cerebellopontine cistern arteriovenous malformation nidus with a large posterior draining vein .

Arachnoid Cyst in CPA Axial T2 FS MR shows a right CPA arachnoid cyst , which exerts mild mass effect upon the cisternal segments of the vestibulocochlear and facial nerves . The cyst also flattens the lateral cerebellum. This cyst follows CSF signal intensity on all sequences.

Venous Malformation ("Hemangioma") in IAC Coronal T1 C+ MR of an lAC venous malformation shows a lateral IAC enhancing mass with focus of internal low signal intensity from punctate intralesional calcification .

Additional Images

Vascular Loop Syndrome Affecting CNVII Axial T2 MR shows a markedly asymmetric left vertebral artery lifting the posterior inferior cerebellar artery into the medial aspect of the CPA cistern in the CNVII root exit zone vicinity.

Epidermoid Cyst in CPA Axial T2 MR demonstrates a right CPA cistern epidermoid cyst with penetration of the porus acusticus and lobulated mass effect on the lateral margin of the brachium pontis .

Arachnoid Cyst in CPA Axial T2 MR through the CPA cistern reveals a CSF intensity arachnoid cyst on the left . The arachnoid cyst flattens the cerebellar hemisphere and bows the facial and vestibulocochlear nerves anteromedially.

Epidermoid Cyst in CPA Axial T2 MR shows a right CPA cistern epidermoid cyst scalloping the cerebellar contour and bowing the cisternal facial nerve anteriorly . The root exit zone is also affected .

Meningioma in CPA Axial T2 MR reveals a dural-based CPA mass with IAC penetration with a "CSF-vascular cleft" between it and the adjacent brachium pontis-pons. Note the normal root exit zone of the contralateral left CNVII .

Aneurysm in CPA-IAC Axial T1 MR shows complex signal associated with a vertebral artery aneurysm . The aneurysm is wedged into the medial CPA cistern in the immediate vicinity of the CNVII root exit zone.

Facial Nerve Schwannoma in CPA-IAC Axial T1 C+ MR shows a small facial nerve schwannoma of the lateral IAC , labyrinthine segment , and geniculate ganglion portions of the facial nerve.

Facial Nerve Schwannoma in T-Bone Axial T1 C+ MR demonstrates a mastoid segment facial nerve schwannoma . Notice that the enhancing tumor has dehisced the posterior wall of the external auditory canal .

Multiple Sclerosis Axial T2 MR shows a multiple sclerosis plaque situated in the lateral right pons near the root exit zone of the facial nerve. Note a 2nd more subtle plaque in the left cerebellum .