hi let's talk about facial nerve palsy also known as Bell's palsy in this video we'll discuss facial
nerve palsy and how one may distinguish between facial nerve palsy and a cerebrovascular accident
a CVA or a stroke but first we should tip our hats to the the person who first described facial
nerve palsy that would be Sir Charles Bell so our Sir Charles Bell was a Scottish anatomist
neurologist and surgeon who among being the the first individual to describe a facial nerve
palsy was also the first person to describe the differences between motor and sensory nerves in
the spinal cord so the honorific of Bell's palsy which we use interchangeably with facial nerve
paralysis comes from Sir Charles Bell so what is a facial nerve palsy well these these palsies
or these paresis pareses are the result of of damage to the facial nerve and as a consequence
of that the ipsilateral or same sided facial muscles are either paralyzed or they're weakened
there are a couple of other symptoms that they may accompany a facial nerve palsy so it's a lateral
hyper lacrimation so a diminished capacity for tears on the affected side and that's because the
the facial nerve if it's damaged hi say either at at the brainstem or in the the facial canal
then that could affect the greater petrosal nerve that's the nerve which carries the the
preganglionic parasympathetic fibers to the pterygopalatine ganglion which serves the
lacrimal gland there can also be if so lateral hypo salivation and that's because the chorda
tympani which also arises in that facial canal carries preganglionic parasympathetics to the
submandibular ganglion which is servicing both the sublingual and submandibular glands there's
also the potential for ipsiateral ageusia which is a lack of taste from the anterior tongue
again because of our good friend chorda tympani and there's the possibility for but clinically
it's exceedingly rare for hyperacusis and that is for sound to seem too loud for a person and
that's because coming off of the the facial nerve and the facial canal the nerve to the
stapedius which is a muscle in the middle ear that helps to dampen sound again that's that's pretty
rare the the dead giveaway for Bell's palsy is the the ipsilateral paralysis or paresis so if
we're looking at at this individual you can see the the complete absence of furrow lines on the
brow the the upper eyelid is drooping so there's a little bit of ptosis there sometimes even the
lower eyelid is is drooping the angle of the mouth you can see takes a diminished downward turn and
many of those lines that that we would see on the face they just they don't appear with the
the same vigor except maybe to accentuate the sagging of skin on the side that is affected so
this is all deal to a an injury or a compression on the facial nerve and it can be anywhere along
the facial nerve there are many different possible causes herpes simplex virus is epstein-barr virus
is edema or swelling can compress the nerve so either is the result of injury or exposure to
cold this is a known sometimes sequelae to to pregnancy but most of the times a facial
nerve palsy is idiopathic we just don't simply understand the the underlying cause for it and
again this typically presents as if so lateral to the side of the injury but there are instances of
bilateral Bell's palsy usually these accompany like a guillain barre a syndrome or a Lyme disease or
something that that may affect the the nuclei of the the facial nerves in the brain stem so
in differentiating Bell's or facial nerve palsy from a cerebrovascular accident or stroke which
is another potential cause for facial nerve paralysis it's good to to understand where
the lesion whether it's a lesion to the facial nerve or a lesion to an upper motor neuron in
the in the brain could occur and what impacts that might have on an individual so let's just
start over here towards the the distal end of the nerve and kind of work our way back
so the the facial nerve just to review has two major divisions the is the temporofacial and
the cervical facial and the the temporal facial division gives rise to these temporal branches
and some to the zygomatic branches and so this division predominantly is going to serve the
frontal belly of occipitofrontalis and it will be complementary to orbicularis oculi as well so
that that's that's an important fact to understand as as we walk our way through this so upper motor
neurons you know controlling the the facial muscles are coming from the the cerebral cortex
and they're going to descend down through to the the pons and in the process of this descent they
decussate or they they crossover so here let's let's follow the yellow here as it comes down
and some of the yellow stays on the same side but most of the yellow is crossing over to the
opposite side now as we follow the yellow so here it is exiting there's the the facial nerve from
the brainstem going out right now to the facial canal makes kind of a z shape through that canal
and then it's again exiting from the skull through that stylomastoid foramen and as you can see the
bulk of that yellow is servicing the cervical facial division exclusively down there whereas
the temporal facial division is a mix of fibers coming from the right side as well as fibers
coming from the left side and so what we see here is that those temporal facial fibers they're being
sourced bilaterally in the brain and the cervical facial fibers are sourced unilaterally so if there
is let's erase some of this let's imagine that there is a cerebrovascular accident that affects
these upper motor neurons high in the cortex CVA affects that as a result an individual is going
to lose their contralateral tone of the cervical facial muscles whereas the temporal facial muscles
frontal belly in part orbicularis oculi should still have some function to them so a person with
cerebral vascular accident is more likely well I should say cerebrovascular accident affecting the
facial nerve is more likely to have contralateral lower face paralysis whereas with facial nerve
erase all of this or it's a facial nerve if the lesion is say in the in the facial canal even
before it comes out of the style of mastoid foramen you're knocking out all of the facial
nerve functions to the face and therefore the entirety of the ipsilateral same sided face
will be paralyzed or or weakened so that should lead us to our assessment question you know in
this scenario you are the the dentist and after administering an inferior alveolar block you were
briefly pulled away for a consult you returned to your patient and they were accompanied to chair
side the whole time by your assistant and you notice that there's a unilateral loss of facial
muscle tone whoa you calmly instruct the patient to smile maybe you don't tell them to smile maybe
you say something charming or funny and you notice that there is absolutely no furrowing
of their forehead is this an encouraging ie a good sign a no call nine-one-one it's an
emergency potential stroke on the differential B yes so the the keys to this question let's see
what were you doing well you were administering an anesthetic to the I am so you know who knows
what that could have done and then you see unilateral loss of facial facial muscle tone
that's problematic and when they're instructed to to smile to really use those facial muscles
or when you coax them into it you see no furling of their forehead therefore there's a complete
unilateral paralysis
complete unilateral paralysis is suggesting that the entirety of the facial nerve has been somehow
compromised or diminished and as a result of that it's most likely that what you're witnessing is
the the nascent formation of of bells and probably what has happened in this situation is that you
missed your target for your I am and this would be a huge whoops you probably went way too far
posteriorly on the ramus of the mandible and you could have hit a deep part of the parotid gland
or perhaps infiltrated into the the capsule of the parotid gland and that anaesthetic then bathed the
branches of the facial nerve as they traversed the gland your patient probably isn't going to
be very happy as a result but it is very likely not in emergency thank you very much for your time