Imaging in Acute Facial Nerve Paralysis M Castillo, MD, FACR Department of Radiology University of North Carolina, Chapel Hill

Overview of Presentation Introduction Review of facial nerve anatomy Clinical and Imaging features of Bell’s palsy Typical Atypical Other causes of acute facial paralysis

Introduction Bell’s palsy accounts for 75% of cases of acute facial nerve (7th cranial nerve) paralysis Imaging is not needed in majority of patients unless they have atypical features W/atypical features, MR & CT may demonstrate potentially treatable lesions affecting facial nerves Facial nerves can be affected anywhere along their course

Anatomy Review Facial nerve nuclei lie in reticular formation of brainstem, ventral to floor (tegmentum) of 4th ventricle(4) Motor Nuclei: Efferent fibers surround nuclei of CN VI & form small mounds on floor of 4th ventricle (facial colliculi) Non-Motor Nuclei: Salivatory Solitary Facial colliculus

7th nerve courses into internal auditory canal (IAC) Efferent fibers surround 6th CN nucleus & exit at cerebellopontine angle (CPA) 7th nerve courses into internal auditory canal (IAC) Within superior anterior quadrant(6) Ant Post

Exits IAC via Fallopian canal Narrowest point throughout entire course Felt to be culprit in facial nerve compression in Bell’s palsy & other causes of nerve swelling

Progress to geniculate ganglion Gives rise to greater superficial petrosal nerve Contains taste axons from tongue & somatic fibers

Fibers then course posteriorly under lateral semicircular canal in middle ear (tympanic portion) Fibers angle back & inferiorly at “second genu” diving the descending canal Here last somatic & parasympathetic fibers separate from facial nerve via the chorda tympani nerve Mastoid segment Tympanic Portion

Facial nerve exits skull base at stylomastoid foramen Facial nerve angles superiorly & anteriorly behind posterior margin of vertical mandibular ramus Just before entering parotid gland, inferior branches originate Posterior auricular, digastric & stylohyoid Within substance of parotid gland, superior branches arise Temporal, zygomatic, buccal, orbicularis oris, mandibular & cervical

Clinical Signs Suggesting Site of Facial Nerve Lesion Upper facial territory is supplied by bilateral motor cortices Lower facial territory is supplied only by contralateral motor cortex Therefore, unilateral central lesions spare upper face Lesions distal to geniculate ganglion Mostly motor abnormalities Lesions proximal to geniculate ganglion Motor, gustatory & autonomic abnormalities

Typical Bell’s Palsy Incidence Etiology not entirely understood 15–30 per 100,000 Usually during winter Etiology not entirely understood Possibly viral (Herpes Simplex Virus) or idiopathic Viral infection of facial nerve results in demyelination, inflammation & swelling Traps nerve in narrow confines of fallopian canal Diagnosis of exclusion Made only when clinical & imaging (if necessary) findings are supportive

Typical Bell’s Palsy Usually a clinical diagnosis Acute onset unilateral (lower or upper) facial paralysis, posterior auricular pain, decreased tearing, hyperacusis (30%) & disturbances of taste By physical examination, Bell’s palsy divided according to classification by House and Brackman Grades 1 & 2 have better outcomes with worse outcome as grade increases. 80-90% recover completely Over age 60, only 40% recover completely

Imaging in Typical Bell’s Palsy Imaging in typical Bell’s palsy is not usually necessary When necessary, MRI is best Normal facial nerve distal to geniculate ganglion may enhance Facial nerve proximal to geniculate ganglion does not normally enhance In patients with Bell’s palsy, enhancement of facial nerve in fallopian & ICA is typical

C/o Dr. M. Michel, Wisconsin

Atypical Bell’s Palsy Clinical features Numbness is not unusual Slower onset of symptoms Bilateral Recurrence Numbness is not unusual Progression beyond seven days suggests another cause

Imaging in Atypical Bell’s Palsy C/o Dr. M. Michel, Wisconsin

Alternative Causes of Acute Facial Nerve Paralysis Atypical signs & symptoms which suggest etiology other than Bell’s palsy require imaging Clinical history is crucial in distinguishing etiologies Choice of imaging technique depends on clinical suspicion

Lyme Disease Lyme disease (borreliosis) Endemic areas (Northeast USA, central Europe, Scandinavia, Canada) Consider in children w/atypical facial palsy Imaging: small white matter lesions similar to multiple sclerosis, enhancement of facial & other cranial nerves Bilateral facial paralysis: 25% Important to make diagnosis early because it is curable early w/antibiotics

Ramsay Hunt Syndrome Caused by reactivation varicella zoster virus (herpes virus type 3) Facial paralysis + hearing loss +/- vertigo Herpes zoster oticus Two-thirds of patients have rash around ear Other cranial nerves, particularly trigeminal nerves (5th CN) often involved Worse prognosis than Bell’s (complete recovery: 50%) Important cause of facial paralysis in children 6-15 years old

C/o Dr. M. Michel, Wisconsin

Infectious causes Acute facial paralysis may result from bacterial or tuberculous infection of middle ear, mastoid & necrotizing otitis externa Incidence of facial paralysis with otitis media: 0.16% Infection extends via bone dehiscences to nerve in fallopian canal leading to swelling, compression & eventually vascular compromise & ischemia Immune compromised patients are at risk for pseudomona infection Poor prognosis (complete recovery is < 50%)

Tuberculosis

Parotid & peri-parotid disease

HIV Infection

Bezold’s abscess & coalescent mastoiditis

Trauma Most acute post traumatic facial palsies are due to t-bone fractures Historically fractures classified as longitudinal or transverse with transverse carrying risk of permanent paralysis Longitudinal fracture usually leads to temporary paralysis from concussion & swelling of nerve Transverse fracture can lead to transection of nerve In all types of paralysis due to fracture, usually the region of geniculate ganglion is involved

Neoplasms 27% of patients with tumors involving the facial nerve develop acute facial paralysis Most common causes: schwannomas, hemangiomas (usually near geniculate ganglion) & perineural spread such as with head and neck carcinoma, lymphoma & leukemia Other neoplasms can also involve the facial nerve Adults: metatstatic disease, glomus tumors, vestibular schwannomas & meningiomas Children: eosinophilic granuloma & sarcomas

Hemangioma

Hemangioma

Facial Nerve Schwannoma

Perineural Tumor Spread

Glomus Tumor Glomus tumors arising from jugular bulb (jugulare) and/or middle ear (tympanicum) may involve the facial nerve M

Rhabdomyosarcoma & squamous cell carcinoma of the EAC Other tumors Rhabdomyosarcoma & squamous cell carcinoma of the EAC

Vestibular Schwannoma Common tumor However, facial nerve is resistant to compression Therefore, tends to produce facial paralysis mostly when they attain a large size

Vestibular Schwannoma -Common tumor -However, facial nerve is resistant to compression, thus, tends to produce facial paralysis mostly when they attain a large size

Meningioma Second most common primary tumor of cerebellopontine angle Rarely results in facial paralysis

Rhabdomyosarcoma

Miscellaneous Causes

Hypertrophic Polyneuropathy Hypertrophic polyneuropathies occasionally lead to facial paralysis

Wegener’s Granulomatosis

Other Causes Guillain-Barre Syndrome Ascending paralysis Iatrogenic Temporal bone surgery Excision of vestibular schwannoma has <10% chance of paralysis Middle ear surgeries Babies who required forceps delivery >90% recovery

Melkersson-Rosenthal Syndrome Acute episodes of facial paralysis Facial swelling Fissured tongue “Scrotal” tongue Very rare Familial but sporadic Usually begins in adolescence Leads to facial disfigurement No definite therapy

Conclusion While Bell’s palsy does not typically require imaging for diagnosis, imaging evaluation is important in the work-up of patients with atypical or unusual presentations of acute facial nerve paralysis, identification of discreet lesions may lead to a change in management of these patients.