Facial Nerve Paralysis

Posted by e-Medical PPT Sunday, June 3, 2012
Course of the Facial Nerve
Intracranial – Arises at the pontomedullary junction and courses with CNVIII to the internal acoustic meatus - 12mm
Meatal – Anterior to the superior vestibular nerve and superior to the cochlear nerve – 10mm
Intratemporal –
Labyrinthe segment
Passes through narrowest part of fallopian canal - 12mm
Narrowest part of facial nerve. The most susceptible to compression secondary to edema.
Tympanic segment
From geniculate ganglion to pyramidal turn – 11mm
Mastoid segment
Exits the stylomastoid foramen – 13mm
Extracranial – From stylomastoid foramen to pes anserinus

Blood supply to facial nerve – clinical relevance
Courses between the epineurium and periosteum – making the blood supply at risk when mobilizing at the first genu
Stylomastoid artery (branch of the postauricular artery of external carotid artery)
Greater petrosal artery (branch of middle meningeal artery)
Internal auditory artery (branch of the AICA)
Labyrinthe segment - lacks anastomosing arterial cascades thereby making the area vulnerable to ischemia

Work Up
Basic labs, thyroid function panel, Lyme titers ELISA for antibodies
Stapedial reflex
MRI with gadolinium / CT
Nerve Excitability Test, Maximal Stimulation Test, Electroneuronography (EnoG) - Useful 72 hours post-injury

Topognostic Testing
Schirmer test for lacrimation
Stapedial reflex test (stapedial branch)
Taste testing (chorda tympani nerve)
Salivary flow rates and pH (chorda tympani)

Stapedial Reflex
Stapedius branch of the facial nerve
Most objective and reproducible
A loud tone is presented to either the ipsilateral or contralateral ear  evokes a reflex movement of the stapedius muscle  changes the tension on the TM (which must be intact for a valid test) resulting in a change in the impedance of the ossicular chain
If intact stapedial reflex, complete recovery can be expected to begin within six weeks
Absence of the stapedial reflex during the first two weeks in Bell’s Palsy is common

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