FACIAL NERVE INJURY

Stapedius

Stapedius is a small muscle in the ear innervated by the facial nerve. It dampens large vibrations of the stapes and the tympanic membrane; this allows the ear to diminish loud noises. If the facial nerve is paralyzed (as seen with Bell’s palsy), the nerve to stapedius is lost, and the ear cannot lessen the vibrations of stapedius. This causes hyperacusis.

Immediate onset paralysis due to fracture of mastoid (temporal bone) requires surgery (decompression, re-anastomosis or cable nerve graft).

Temporal bone fractures have been classified by orientation with respect to the long axis of the petrous portion of the temporal bone.

Longitudinal fractures make up 70 to 90% of temporal bone fractures, and transverse fractures make up 10 to 30%. Some fractures may have characteristics of both patterns.

• Infection
• Labrynthitis ossificans
• Mucosalization of the middle ear
• Facial nerve injury
• CSF leak
• Encephalocele

None

B i.e. Transverse

Ans. is ‘b’ i.e., Middle cranial fossa 

Ans is ‘a’ i.e. Immediate repair

During mastoidectomy, when the facial nerve is injured, it is immediately explored. Injury to greater than 50% of the neural diameter of the facial nerve is addressed either with primary reanastomosis or reconstructed with the use of a nerve graft. Complete recovery of nerve function is uncommon in these cases.

Ans is b i.e inferior belly of omohyoid

Facial nerve paralysis is a daunting potential complication of parotid surgery. Knowledge of the key landmarks of the facial nerve trunk is essential for safe and effective surgical intervention in the region of the parotid gland. In current practice, wide ranges of landmarks are used to identify the facial nerve trunk, however, there is much debate in the literature about the safety and reliability of each of these landmarks.

• Major surgical landmarks to the facial nerve include

the tympanomastoid suture line,

the tragal pointer,

the posterior belly of the digastric muscle.

the retromandibular vein,and

–        the styloid process of the temporal bone.

• The tympanomastoid fissure- The most used anatomical landmark is the tympanomastoid fissure. The tympanomastoid fissure lies between the mastoid and tympanic segments of the temporal bone. The facial nerve lies approximately 6-8 mm medial to suture.
• The Tragal pointer- the nerve is usually located inferior and medial to the Tragal pointer of the external auditory canal, about 1 Omm.
• The Digastric muscle- The facial nerve lies just superior and on the same plane as the plane of digastric muscle attachment.
• If the main trunk of facial nerve cannot be readily identified, retrograde dissection of a branch of facial nerve can be used. The buccal branch is best for this approach.
• In the infant and young child, these landmarks are not applicable because of differences in the rate of anatomic development of the parotid gland and mastoid.

For lacrimation, greater superficial petrosal nerve which is a branch of facial nerve is responsible

It arises from the geniculate ganglion/any lesion occurring at the level of geniculate ganglion will injure this branch and will lead to dryness of eyes.

Ans. A Loss of Corneal reflex at the side of lesion

Course of Facial Nerve

• Below stylomastoid formen, facial nerve gives following branches: Posterior auricular branch, muscular branches (stylohyoid and posterior belly of diagastric) and terminal (peripheral) branches.
• Lesion at sternomastoid foramen

i. Will spare:

– Greater superficial petrosal nerve -7 Lacrimation present.

– Nerve to stapedius -7 Normal stapedial reflex and no hyperacusis.

– Chorda tympani -7 Normal salivation and taste sensation in anterior 2/3 of tongue.

ii. Will involve:

Terminal (peripheral) branches -7 Paralysis of muscles of facial expression. Corneal reflex will also be lost because efferent fibres of corneal reflex are derived from peripheral branches of facial nerve (it is a LMN type lesion).

Remember:

Corneal Reflex: Afferent: Trigeminal nerve

Efferent: Peripheral branches of facial nerve

• Lesion occuring at the outlet of stylomastoid foramen means LMN palsy, so face sags and is drawn across to opposite side. 
• Chorda tympani nerve is spared at this level hence taste sensation over anterior 2/3 of tongue preserved

Other Operations where Facial Nerve may be Damaged

–         Stapedectomy

–         Removal of acoustic neuroma

Ans. is. B. Transverse fractures

Malignant otitis externa (MOE), also known as necrotizing otitis externa, is an invasive bacterial infection that involves the external auditory canal and skull base. It is a complication of external otitis externa that occurs in immunocompromised patients.Pseudomonas aeruginosa is causative in 95% of cases.

Otitis externa is typically seen in elderly diabetic patients. Diabetics have an increased pH in cerumen which facilitates growth of pseudomonas

Physical examination findings:

• Ear canal erythema with purulent discharge – Granulation tissue visible in the inferior portion of the external auditory canal at the site of Santorini’s fissure (vertical fissure in the cartilaginous canal of the external auditory meatus) is pathognomic; this finding may be absent in atypical patients (e.g., HIV infected and children).
• Conductive hearing loss.
• Lymphadenopathy of the postauricular, preauricular, and lateral cervical lymph nodes.
• Cranial nerve palsies – As the infection advances, osteomyelitis of the skull and TMJ can develop resulting in CN palsies. Involvement of the stylomastoid foramen will lead to facial paralysis in 25% of patients; less frequently, involvement of the jugular foramen leads to deficits in cranial nerves IX, X, and XI; children have a higher incidence of facial palsy due to their relatively undeveloped mastoid process and more medical location of the fissure of Santorini which places the facial nerve in closer proximity to the ear canal.
• Central nervous system complications – These are rare but are the most common cause of death in MOE: meningitis; brain abscess; dural sinus thrombophlebitis.

• Facial Nerve descends in the posterior wall of the middle ear, behind the pyramid, and emerges through the stylomastoid foramen into the neck.
• The greater petrosal nerve arises from the facial nerve at the geniculate ganglion.
• It contains secretomotor (parasympathetic) fibers to the lacrimal gland, submandibular and sublingual salivary glands, and the glands of the nose, the palate and the pharynx
• The nerve is joined by the deep petrosal nerve from the sympathetic plexus and forms the nerve of the pterygoid canal which ends in the pterygopalatine ganglion.
• The nerve to the stapedius arises from the facial nerve which supplies the muscle within the pyramid.
• The chorda tympani arises from the facial nerve just above the stylomastoid foramen. The nerve leaves the middle ear through the petrotympanic fissure and enters the infratemporal fossa, where it joins the lingual nerve. The chorda tympani contains taste fibers from the mucous membrane covering the anterior two-thirds of the tongue (not the vallate papillae) and the floor of the mouth.

• The facial muscles are innervated by the facial nerve.
• Damage to the facial nerve in the internal acoustic meatus (by a tumor), in the middle ear (by infection or operation), in the facial nerve canal (perineuritis, Bell’s palsy), or in the parotid gland (by a tumor) or caused by lacerations of the face will cause distortion of the face, with drooping of the lower eyelid, and the angle of the mouth will sag on the affected side. This is essentially a lower motor neuron lesion.
• Check voluntary movement of the upper part of the face on the affected side: in supranuclear lesions such as a cortical stroke (upper motor neuron; above the facial nucleus in the pons), the upper third of the face is spared while the lower two-thirds are paralyzed.
• The orbicularis, frontalis, and corrugator muscles are innervated bilaterally, which explains the pattern of facial paralysis in these cases

Ans. B: Paralysis of the lower half of face on the opposite side

The facial motor nucleus has dorsal and ventral divisions that contain lower motor neurons supplying the muscles of the upper and lower face, respectively.

• The dorsal division receives bilateral upper motor neuron input (ie, from both sides of the brain).
• The ventral division receives only contralateral input (ie, from the opposite side of the brain).

Thus, lesions of the corticobulbar tract between the cerebral cortex and the facial motor nucleus destroy or reduce input to the ventral division, but ipsilateral input (ie, from the same side) to the dorsal division is retained. As a result, central facial palsy (damage to upper motor neurons of the facial nerve) is characterized by hemiparalysis or hemiparesis of the contralateral muscles of facial expression, but not the muscles of the forehead.

Ans. is ‘d’^‘ i.e., All of the above

Causes of facial paralysis

• Central :- Brain abscess, pontine glioma, Polio, multiple sclerosis
• Intracranial part (cerebellopontine angle) :- Acoustic neuroma, meningioma, congenital cholesteatoma, metastatic carcinoma, meningitis
• Intratemporal part :-
• Idiopathic :- Bell’s palsy, Melkersson’s syndrome
• Infections :- ASOM, CSOM, Herpes zoster oticus, malignant otitis externa
• Trauma :- Surgical (mastoidectomy, stapedectomy), accidental (fractures of temporal bone)
• Neoplasms :- Malignancies of external and middle ear, glomus jugular, facial nerve neuroma, metastasis (from breast, lung etc).
• Extracranial part :- Malignancies or surgery or injury to parotid gland
• Systemic diseases :- Diabetes, hypothyroidism, uremia, PAN, Sarcoidosis (Heerfordt’s syndrome), leprosy, leukaemia, demyelinating disease

Ans. is ‘c’ i.e., Greater superficial petrosal nerve 

• In facial nerve injury :-

1. Loss of lacrimation :- Due to involvment of greater superficial petrosal nerve.
2. Loss of stapedial reflex :- Due to involvement of nerve to stapedius.
3. Lack of salivation :- Due to chordatympani.
4. Loss of taste sensation from Anterior 2/3 of tongue : – due to chordatympani.
5. Paralysis of muscle of facial expression :- Due to terminal (peripheral) branches.
6. Hyperacusis (intolerance to loud noice) :- Due to involvement of nerve to stapedius (causing parolysis of stapedius).