Facial Nerve Anatomy and Bell Palsy
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Direct answer
The facial nerve runs from the pons through the internal auditory meatus, the narrow labyrinthine canal, the tympanic and mastoid segments of the temporal bone, and exits at the stylomastoid foramen to supply the muscles of facial expression. Within the temporal bone it gives off the greater petrosal nerve, the nerve to stapedius and the chorda tympani. Bell palsy is an acute, idiopathic lower motor neuron paralysis of this nerve, treated with early oral corticosteroids and meticulous eye protection.
What you must remember
- Intratemporal course: meatal segment with the vestibulocochlear nerve; labyrinthine segment — the narrowest bony canal — to the geniculate ganglion; horizontal (tympanic) segment above the oval window; vertical (mastoid) segment to the stylomastoid foramen.
- Branches inside the temporal bone: greater petrosal nerve for lacrimation, nerve to stapedius (its paralysis causes hyperacusis), and chorda tympani carrying taste from the anterior two-thirds of the tongue and supply to the submandibular and sublingual glands.
- Lower versus upper motor neuron signs: an LMN lesion paralyses the whole hemiface including the forehead; an UMN lesion spares the forehead because of bilateral upper facial cortical innervation.
- Causes of LMN palsy to recite: Bell palsy, Ramsay Hunt syndrome (herpes zoster oticus with vesicles and pain in the ear), otitis media and cholesteatoma, parotid tumours, acoustic neuroma and cerebellopontine angle lesions, trauma, and diabetes.
- Bell palsy management: oral corticosteroids started within 72 hours of onset give the best chance of recovery; antivirals are added for severe palsies or Ramsay Hunt; physiotherapy supports recovery.
- Eye care is mandatory: exposure keratitis is prevented with lubricating drops, ointment and taping at night, with eyelid procedures or gold weight implantation if recovery is poor.
- Grading and prognosis: severity and recovery are graded by the House-Brackmann scale from I (normal) to VI (total paralysis); most patients recover well, though complete palsy with pain warns of poorer outcome.
Common confusion
Students mislabel a forehead-sparing palsy as Bell palsy — if the frontalis wrinkles, the lesion is upper motor neuron and the cause may be intracranial. Also do not stop at the diagnosis of Bell palsy without excluding ear disease: otoscopy for vesicles, cholesteatoma or discharge is part of every facial palsy assessment.
Exam-focused takeaway
For theory, draw the intratemporal course with the three branches and their functions, then define Bell palsy and give its management with eye care emphasised. In viva, expect the differences between UMN and LMN palsies, the cause of hyperacusis and loss of taste, and when imaging is needed. In the posting, grade every palsy with the House-Brackmann scale and examine the ear, parotid and cornea — that sequence is what examiners watch for.
Frequently asked questions
Why is the forehead spared in upper motor neuron palsy?
The upper facial nucleus receives corticobulbar fibres from both hemispheres, so a unilateral cortical lesion leaves frontalis functioning; an LMN lesion paralyses the whole half of the face.
What is Ramsay Hunt syndrome?
Herpes zoster infection of the geniculate ganglion, presenting with ear pain, vesicles in the auricle and canal, facial palsy and sometimes sensorineural hearing loss.
Which branch causes hyperacusis when involved?
The nerve to stapedius; paralysis of stapedius leaves the stapes undamped so ordinary sounds seem unpleasantly loud.
What is the first-line treatment of Bell palsy?
Oral corticosteroids begun within 72 hours of onset, with antiviral cover in severe or zoster-related cases, plus eye protection from day one.
How is facial palsy graded?
The House-Brackmann scale, from grade I (normal) to grade VI (complete paralysis).
Which features demand imaging in facial palsy?
Progressive palsy, associated deafness or vertigo, vesicles, other cranial neuropathies, or failure to recover — imaging then searches for cholesteatoma or a neoplasm.