Facial Nerve Test
Jiranut Chaibhuddanugul,MD.
Facial Nerve Test
• Topognostic test
• Electrophysiologic testing
• Unconventional test
HOUSE-BRACKMANN FACIAL NERVE GRADING
SYSTEM
HOUSE-BRACKMANN FACIAL NERVE GRADING
SYSTEM
HOUSE-BRACKMANN FACIAL NERVE GRADING
SYSTEM
 Common mistake !!!
 Upper eye lid movement
 Remember
: Levator palpebrae m is innervated by
oculomotor N. (CN III)
 remain intact despite
total facial N paralysis.
K.J. Lee essential otolaryngology
Topognostic test
• Simple principle: lesions below the point at which a
particular branch leaves the facial nerve trunk will spare
the function subserved by that branch.
• Complete focal lesion such trauma, topognostic tests are
reliable but usually are unnecessary.
Topognostic test
• Bell's palsy usually is a mixed and partial lesion with
varying degrees of conduction block and degeneration
changes within different fibers and fascicles of the nerve
trunk.
• Topognostic tests are not expected to provide precise
information about the level of the lesion.
• In recent years, otologists use these tests only rarely.
Lacrimal Function
• Schirmer's test
• Places a folded strip of sterile filter paper into the
conjunctival fornix of each eye and compares the rate of
tear production of the two sides.
• The length of the wetted portion of the strip after a fixed
interval (usually 5 minutes) is measured.
• Positive if the affected side shows less than one-half the
amount of lacrimation seen on the healthy side.
Lacrimal Function
• A total response (sum of the lengths of wetted filter paper
for both eyes) of less than 25 mm is considered abnormal.
• Decrease to 25% of normal in any of these was associated
with a 90% chance of a poor recovery.
• Advantages
Simplicity, speed, and economy.
Evaluation protective mechanism of eye.
• Disadvantages
Accuracy 60%
Not useful as prognostic test
Reflex is consensual ; Decrease tearing ,Excessive tearing
Stapedius Reflex
• In patients with hearing loss, acoustic reflex testing is used
to assess the afferent (auditory) limb of the reflex, but in
cases of facial paralysis, the same test is used to assess
the efferent (facial motor) limb.
• An absent reflex or a reflex that is less than one-half the
amplitude of the contralateral side is considered abnormal.
• It is absent in 69% of cases of Bell's palsy (in 84% when
the paralysis is complete).
• No prognostic value.
Taste
• Chorda tympani - taste from the anterior two thirds of the
tongue.
• Filter paper disks impregnated with aqueous solutions of
salt, sugar, citrate, or quinine.
• Electrical stimulation (electrogustometry ; EGM) threshold responses are denoted by the current level's
imparting a subjective sensation of one of the four cardinal
tastes or of buzzing or tingling.
Taste
• In healthy persons, the two sides of the tongue have
similar thresholds for electrical stimulation, rarely differing
by greater than 25%.
• Little usefulness of taste testing, because results were
abnormal in almost all patients who were in the acute
phase of Bell's palsy and could not identify patients with a
poor prognosis.
Taste
Salivary Flow Test
• Cannulation of the submandibular ducts and comparison of
stimulated flow rates on the two sides.
• Lesion at or proximal to the point at which the chorda
tympani nerve leaves the main facial trunk ; variable and
may be anywhere in the vertical (mastoid) portion of the
nerve.
• Reduced salivary flow (less than 45% of flow on the healthy
side after stimulation with 6% citric acid) correlates well with
worse outcome in Bell's palsy ;
accuracy 85%.
Salivary pH
• Submandibular salivary pH of 6.1 or less predicts
incomplete recovery in cases of Bell's palsy.
• Only the duct on the affected side needs to be cannulated.
• Overall accuracy of prediction was 91%.
• Reported experience with salivary pH is very limited; it is
unknown whether this test gives an earlier prognosis than
other tests.
Imaging
• MRI with intravenous gadolinium contrast : study of choice
when a facial nerve tumor is suspected in the
cerebellopontine angle and temporal bone.
• However, enhancement also occurs in most cases of Bell's
palsy and herpes zoster oticus, usually in the
perigeniculate portions of the nerve.
• May persist for more than 1 year after clinical recovery and
no apparent prognostic significance.
Imaging
• MRI shows the greatest utility in predicting location and
depth of parotid gland tumors, but even in this capacity it is
no better than simple manual palpation alone.
• CT is valuable for surgical planning in cholesteatomas and
temporal bone trauma.
• Less useful than MRI in the investigation of atypical
idiopathic paralysis.
Electrophysiologic testing
Sunderland classification
Neurapraxia
Axonotmesis
Neurotmesis
Sunderland Class I
• No physical disruption of axonal continuity occurs.
• Supportive connective tissue elements remain intact.
• Conduction block, no impulses can cross the area of
the lesion, but electrical stimulation distal to the lesion
still produces a propagated action potential and a
visible muscle twitch at all times after injury.
Sunderland Class II
• Axonal disruption without injury to supporting structures.
• Wallerian degeneration occurs and propagates distally
from the site of injury to the motor end plate and
proximally to the first adjacent node of Ranvier.
• Connective tissue elements remain viable, so
regenerating axons may return precisely to their original
destinations.
Sunderland Class III
• Disrupts the endoneurium.
• Wallerian degeneration - regenerating axons are free
to enter the wrong endoneurial tubes or may fail to
enter an endoneurial tube at all.
• Synkinesis.
Sunderland Class IV
• Perineurial disruption
• Incomplete and aberrant regeneration is greater.
• Intraneural scarring prevent most axons from reaching
the muscle - greater synkinesis but incomplete motor
function recovery.
Sunderland Class V
• Complete transection of a nerve.
• Almost no hope for useful regeneration.
Sunderland Class VI
• MacKinnon and associates
• Mixed injury involving both neurapraxia and a
variable degree of neurodegeneration.
• Compressive, inflammatory, or traumatic in origin,
can be heterogeneous in nature, with differing
degrees of injury from fascicle to fascicle.
Electrophysiologic testing
• A patient with a conduction block (class I injury) cannot
move the facial muscles voluntarily, but a facial twitch
can be elicited by transcutaneous electrical stimulation
of the nerve distal to the lesion.
• In classes II to VI, delay wallerian degeneration results
in continued electrical stimulability of the distal segment
for up to 3 to 5 days after injury.
• During these first days after an insult, electrodiagnostic
testing of any form cannot distinguish between
neurapraxic and neurodegenerative injuries.
Electrophysiologic testing
• After wallerian degeneration : Class I / classes II – V.
• Cannot distinguish among the different classes of
neurodegenerative lesions II, III, IV, and V.
• Most facial nerve lesions are not pure but probably
mixed.
• Variable threshold of electrical stimulability
commensurate with the proportion of neural
degeneration across the nerve trunk.
Electrophysiologic testing
Mark May, the facial nerve 2nd edition 2000
Electrophysiologic testing
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•
•
•
Nerve excitability test (NST)
Maximal stimulation test (MST)
Electroneurography (ENoG)
Electromyography (EMG)
Electrophysiologic testing
• Determining prognosis.
• Sometimes in stratifying patients for nonsurgical
versus surgical management.
• Rarely useful in differential diagnosis.
• Intraoperative monitoring of facial nerve function
(usually with electromyography).
Nerve Excitability Test
Hilger stimulator,
model N
Nerve Excitability Test
• The stimulating electrode is placed on the skin over
the stylomastoid foramen or over one of the
peripheral branches of the nerve.
• Beginning with the healthy side, electrical pulses
steadily increasing current levels until a facial twitch is
noted.
• The lowest current eliciting a visible twitch is the
threshold of excitation.
• Next, the process is repeated on the paralyzed side.
Nerve Excitability Test
• A difference of 3.5 milliamperes (mA) or more
– reliable sign of severe degeneration.
– an indicator for surgical decompression.
– Complete versus incomplete recovery can be predicted
with 80% accuracy.
• In a simple conduction block - no difference exists
between the two sides.
• Positive in Sunderland class II – VI.
• Daily examinations, severe degeneration can be
detected as early as possible.
Nerve Excitability Test
• The NET is useful only during the first 2 to 3 weeks of
complete paralysis, before complete degeneration
has occurred.
• This test is unnecessary in cases of incomplete
paralysis, in which the prognosis is always excellent.
• If the paralysis becomes total, the test can determine
whether a pure conduction block exists or whether
degeneration is occurring.
Nerve Excitability Test
• Once excitability is lost and this result is confirmed by
repeat testing, further excitability tests are pointless,
because clinically evident recovery always begins
before any apparent electrical excitability returns
(early deblocking).
• Complete paralysis, if clinical recovery begins before
degeneration is noted, continuing testing is
unnecessary, because recovery will be rapid and
complete.
Nerve Excitability Test
• Because of relatively large intersubject variations in
threshold compared with the small differences
between the two sides of the face.
• Mechelse and associates used as their criterion for
decompression a 150% increase in threshold
compared with the healthy side.
Maximum Stimulation Test
• Nerve-stimulating equipment are the same as in the
NET.
• Maximal stimuli or supramaximal stimuli are used
(Initial 5 mA  to level of patient’s tolerance).
• On the unaffected side, the stimulus current intensity
is increased until the maximum stimulation level.
• Then used to stimulate the affected side, and the
degree of facial contraction is subjectively assessed
as either equal, mildly decreased, markedly
decreased, or without response compared with that
on the normal side.
• (0%, 25%, 50%, 75%, 100%)
Maximum Stimulation Test
• The theoretic basis of the MST is that by stimulating all
intact axons.
• Information should more reliably guide prognosis and
treatment than that obtained with the NET.
• Unfortunately, no good data comparing these, so this
claim has not been proved.
• Sx - no response on injured side at maximal stimulation.
• May and coworkers, in Bell's palsy
– MST normal - 88% of patients recovered completely.
– Reduced movement - 27% chance of complete recovery.
– Absence of electrically stimulated movement –incomplete
recovery.
Electroneuronography (ENoG)
• Facial nerve is stimulated transcutaneously, as in
the NET, although a bipolar stimulating electrode is
used.
• Responses to maximal electrical stimulation of the
two sides are compared, as in the MST, but they
are recorded in a more objective fashion by
measuring the evoked compound muscle action
potential (CMAP) with a second bipolar electrode.
• The average difference in amplitude between the
two sides in healthy patients be only 3%.
Electroneuronography (ENoG)
• Estimate the amout of severe nerve fiber degeneration.
• Example, amplitude of the response on the paralyzed side
is 10% of that on the normal side, an estimated 90% of
fibers are degenerated.
• May and colleagues ; severe ENoG amplitude reductions
(<10% of the unaffected side) were highly correlated with
incomplete recovery and indicated for Sx if degeneration
within 14 days.
Electroneuronography (ENoG)
Electroneuronography (ENoG)
• Most useful between 4 – 21 days after the onset of
complete paralysis.
• Not performed until 4th day , takes 3 days for wallerian
degeneration to occur after severe injury.
• Not useful after 3 weeks, false positive from deblocking.
• Used in Bell’s palsy, trauma, otitis media.
• Not useful in Ramsay Hunt syndrome due to multiple site
of injury.
Glasscock –Shambaugh
Surgery of the Ear, 6th .
Electroneuronography (ENoG)
Tumor: Increase latency + decrease amplitude
Decrease amplitude = increasing tumor size
Bell’s palsy: decrease CMAP amplitude
Mark May, the facial nerve 2nd edition 2000
Electroneuronography (ENoG)
• Patients reaching 95% degeneration within 2 weeks had a 50%
chance of a poor recovery.
• Gradual decrease in ENoG amplitude had a much better
prognosis.
Cumming’s 5th .
• If 90% degeneration dose not occur by 3 weeks after onset of
Bell’s palsy  good prognosis.
• Degeneration > 90% in 14 days of complete paralysis – poor
recovery > 50% of patients.
• Rate of degeneration is important – severe degeneration in 5th
day have poorer prognosis than in several weeks.
Glasscock –Shambaugh ,6th .
Electromyography (EMG)
• Recording of spontaneous and voluntary muscle potentials.
• Role in the early phase of Bell's palsy is limited, because it
does not quantitative estimate the percentage of
degenerated fibers.
• Uses to confirmed surgery when voluntarily active facial
motor units (despite loss of excitability of the nerve trunk)
Electromyography (EMG)
• EMG may give prognostically useful after muscle loss of
excitability.
• After 10 to 14 days, fibrillation potentials may be detected,
confirming the presence of degenerating motor units ; 81%
of patients - incomplete recovery.
• Polyphasic reinnervation potentials, 4 to 6 weeks after the
onset of paralysis, detectable recovery and predicts a fair
to good recovery.
Electromyography (EMG)
• Assessment of long-standing facial paralysis (> 3 weeks)
to determine the possible success of anastomosis or crossfacial anastomosis for restoring facial motion.
• In the setting of acute paralysis (< 3 weeks), the finding of
active motor unit potential in the present of complete
paralysis + > 90% degeneration in EnoG means
deblocking is occur and prognosis is good.
• EMG also can help assess whether a nerve repair is
unsuccessful - no polyphasic reinnervation potentials at 15
months the anastomosis should be considered a failure.
Electromyography (EMG)
EMG-muscle at rest
– A-needle insertion activity
(normal)
– B-positive sharp waves
(~denervation)
– C-fibrillations
(denervation- invisible contraction)
– D-bizarre discharges
(~myopathies and neuropathies)
Mark May, the facial nerve 2nd edition 2000
Electromyography (EMG)
• EMG-muscle contracting
– A-Normal: 50-1500 mV
– B-Partial interference pattern
• Severe neuropathy
– C-small but prolonged
polyphasic motor
• Early nerve regenertion
– D- Short duration lowamplitude triphasic,polyphasic
• Myopathiy
Mark May, the facial nerve 2nd edition 2000
Electromyography (EMG)
Degeneration
: Defibrillation potential
Reinnervation
: Polyphasic potential
Facial Nerve Monitoring
• Simple observation fails to detect many small muscular
contractions and in any case demands constant vigilance.
• Electrodes in or near the facial muscles record EMG potentials
that can be amplified and made audible with a loudspeaker.
• Active : electrical stimulation of the facial nerve is used along
with measurement of facial CMAPs.
• Passive : visually monitor the face for twitches during parotid
surgery, applying needle electrodes to the facial muscles and
recording CMAPs
Facial Nerve Monitoring
 Monopolar electrode
 Activates a wide area (depending on current intensity)
 Sensitive for locating and mapping facial N.
 Best use for tumor mapping
 Flexible with blunt tips  convenient for access to cramped
areas.
 Stimulation of adjacent N. (vestibular and auditory) often
activate facial N.  false-positive.
Facial Nerve Monitoring
 Bipolar electrode
 Best for differentiating neural tissue or facial N form adjacent
neural structure
 Current is mostly confined to tissue bet. forceps tips  quite
specific.
 Small surface area of probe
 reduce possibility of false positive
Facial Nerve Monitoring
– Sound Feed back
Thump / burst
• stimulates the nerve electrically.
• gentle mechanical stimulation (e.g., touching the nerve with an
instrument).
• near-instantaneous nerve stimulation.
popcorn popping / train
• tension on the nerve or caloric or thermal stimulation.
• signify ongoing stimulation of the nerve, which can be
potentially more damaging.
Facial Nerve Monitoring - Errors
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Detached or shorted electrodes.
incorrect wiring of electrodes.
malfunction of a nerve monitor or stimulator
Direct anesthesia of the facial nerve from local anesthetic
infiltration to the stylomastoid foramen.
• Pharmacologic muscular paralysis from induction agents used
in anesthetic management
• Muted speaker.
• nonfunctional nerve.
Facial Nerve Monitoring
False-positive identification
• Stimulation of the trigeminal nerve – Masseter m.
• Stimulation of the adjacent vestibular or cochlear
nerves.
Use in
• Acoustic neuroma surgery
• Skull base surgery
• Parotidectomy
• Middle ear and mastoid surgery
Unconventional Tests of
Facial Nerve Function
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Acoustic Reflex Evoked Potentials
Antidromic Potentials
Blink Reflex
Magnetic Stimulation
Optical Stimulation
Transcranial Electrical Stimulation–Induced Facial Motor
Evoked Potentials
Acoustic Reflex Evoked potentials
• Hammerschlag and associates
• Scalp-recorded potential response to acoustic stimulation
contralateral to the recording site and attributed this to facial
motor pathway activation.
• The response persisted after paralysis during anesthesia intraoperative monitoring of facial nerve function.
• the response was extremely small and slow to record (12- to
15-msec latency).
Antidromic Potentials
• If a motor nerve is electrically or mechanically stimulated, action
potentials will be propagated in two directions
• Orthodromic or antegrade impulse will travel distally toward the
muscle.
• M-wave (muscle action potential) is the same potential recorded in
ENoG.
• Antidromic or retrograde impulse will travel proximally toward the
cell body.
• F-wave antidromic impulse reflected back along that neuron's axon in
an orthodromic direction
• recorded by electrodes on the proximal nerve (near field) or at a
distance (far field).
Antidromic Potentials
• F-waves are easily disrupted by even the mildest degree of
facial paresis, even when clinical examination of facial nerve
function yields normal findings.
• Delayed latency or decreased amplitude or absent in patients
with acoustic tumors.
• However, they do not predict postoperative function.
• Intraoperative facial nerve monitoring - Wedekind and Klug
believe that F-wave monitoring provides earlier and better
prognostic information to the surgeon than that obtained with
continuous EMG monitoring.
Blink Reflex
• Electrical or mechanical stimulation of the supraorbital branch
of the trigeminal nerve elicits a reflex contraction (blink) of the
orbicularis oculi muscle, which is innervated by the facial nerve.
• Two studies found blink reflex abnormalities (recorded by
EMG) in many patients with acoustic tumors (far more than
were found by ENoG).
• Suggests that subclinical facial nerve involvement is more
common than has been clinically appreciated.
• No evidence of any prognostic information to that available
from tumor size.
Optical Stimulation
• Stimulating the facial nerve without direct tissue contact neural stimulation without mechanical trauma.
• Ultraviolet wavelength excimer laser.
• Pulsed short- and medium-wavelength infrared laser light.
• Advantage for use in locations in which mechanical dissection
must be kept to a minimum, such as at the cerebellopontine
angle (does not have a protective layer of epineurium for
support.
Transcranial Electrical Stimulation–
Induced Facial Motor Evoked
Potentials (MEPs)
• Active stimulation - intraoperative facial nerve monitoring.
• Spiral electrodes are placed at Cz and C3/C4 overlying the
facial motor cortex contralateral to the side of the lesion.
• Electrical stimulation of these facial corticobulbar neurons is
propagated across the pyramidal decussation to stimulate
facial nucleus neurons on the side ipsilateral to the lesion.
Transcranial Electrical Stimulation –
Induced Facial MEPs
• Lower motor neuron stimulation propagates to the facial
musculature, where a muscle action potential is recorded.
• The integrity of the entire facial motor tract is tested by this
technique.
• MEP recordings before tumor microdissection (baseline),
intraoperatively and immediately after completion of dissection
(final).
• The final-to-baseline MEP amplitude ratio is calculated to
determine the likelihood of an intact or disrupted facial motor
tract.
Transcranial Electrical Stimulation –
Induced Facial MEPs
Constraints
• Necessity for nonvolatile anesthesia (only propofol and narcotic
infusions are used for maintenance of anesthesia, as volatile
agents adversely affect corticobulbar stimulability).
• Pause surgical dissection during MEP acquisition.
• Possibility of epileptic discharge during cortical stimulation.
Transcranial Electrical Stimulation –
Induced Facial MEPs
• Final-to baseline MEP amplitude ratios greater than 50%
appear to correlate well with good immediate postoperative
facial function (reported as House-Brackmann grade I or II).
• Ratios less than 50% correlate with varying degrees of worse
function (reported as House-Brackmann grades III to VI).
• This technique is in its infancy and is likely to undergo
continued refinement.
Thank You.