Anatomical and physiological features
The course of the VII pair of cranial nerves (n. facialis) originates in the cranial cavity, heading toward the internal acoustic meatus, after which it enters the facial canal of the petrous part of the temporal bone. Inside the canal, it joins the intermediate nerve, which carries taste and secretomotor fibers.
Exiting the canal through the stylomastoid foramen (foramen stylomastoideum), the nerve heads toward the parotid salivary gland. There it forms the parotid plexus, known as the pes anserinus major.
Functionally, the facial nerve provides two key tasks:
- Motor part: innervation of the facial muscles.
- Secretory part: innervation of the lacrimal and salivary glands.
Etiology of the disease
The causes of facial neuropathy are diverse and divided into several main groups:
- Infectious lesions: bacterial (diphtheria, tetanus, syphilis) and viral (including poliomyelitis).
- Middle and inner ear diseases: the inflammatory process causes edema and critical compression of the nerve inside the narrow bony canal.
- Tumors and inflammation: localized at the base of the brain.
- Traumatic injuries: injuries of the middle third of the face, as well as the parotid-masseteric region.
- Iatrogenic (surgical) injuries: occur during operations on the parotid salivary gland or when opening abscesses/phlegmons in the submandibular region (high risk of damage to the marginal mandibular branch).
- Complication of local anesthesia: during mandibular anesthesia, transient dysfunction may occur due to the effect of the anesthetic on the nerve trunk.
Clinical presentation and diagnostics
The basis of the clinical picture is paralysis of the facial muscles on the affected side. Diagnosis begins with assessing the face at rest: the doctor checks the symmetry of the palpebral fissures, the position of the eyebrows and corners of the mouth, the prominence of the nasolabial folds, and the presence of ticks.
The symptom complex of the lesion includes:
- Pronounced facial asymmetry: smoothing of the forehead folds and the nasolabial fold, drooping of the corner of the mouth. When attempting to show teeth, the mouth is skewed toward the healthy side.
- Lagophthalmos ("hare's eye"): inability to close the palpebral fissure.
- Bell's phenomenon: when attempting to close the eyes tightly, the eyeball rolls upward and outward.
- Ophthalmologic complications: impaired tear production (or constant tearing) leads to dryness, conjunctivitis, or keratitis.
- Ageusia: taste disorder (sensitivity to sour and sweet on the anterior 2/3 of the tongue is assessed).
To confirm the diagnosis, mimetic tests are used. The patient is asked to: wrinkle the forehead, frown the eyebrows, tightly close the eyes, bare the teeth, puff out the cheeks, purse the lips, whistle, and "blow out a candle."
Treatment methods
Therapeutic tactics directly depend on the etiology of the disease and include conservative and surgical approaches.
Conservative treatment
- Pharmacotherapy: in viral etiology (in the acute period), human γ-globulin is administered. In bacterial etiology, antibiotics, dehydrating, and desensitizing agents are used. The complex regimen includes calcium preparations, intravenous 40% glucose, B vitamins, anticholinesterase drugs (neostigmine, galantamine), dibazol, ATP, as well as steroid drugs.
- Physiotherapy: UHF therapy, electrophoresis with hydrocortisone, ozokerite and paraffin therapy with ultrasound, facial massage, mud therapy, and hirudotherapy.
Surgical treatment
If conservative measures are ineffective or in case of traumatic rupture, surgical interventions are indicated. They are classified into four groups:
- Restoration of function: decompression of the bony canal, neurolysis, nerve suture, free graft plasty.
- "Revitalization" of mimicry: operations on the sympathetic nervous system.
- Reinnervation: suturing the facial nerve to healthy nerves (accessory, hypoglossal, phrenic).
- Tissue suspension: dynamic (formation of muscle flaps from the masseter/temporal muscle) or static (fascia lata plasty, threads). Corrective operations are also performed (excising excess skin, myotomy on the healthy side).
Briefly: answers to topical questions
What branches does the facial nerve give off in the facial canal?
Within the facial canal, three main branches depart from the intermediate nerve:
- Greater petrosal nerve (n. petrosus major) — provides parasympathetic innervation to the lacrimal gland.
- Nerve to stapedius (n. stapedius) — innervates the stapedius muscle (m. stapedius) and regulates the tension of the tympanic membrane.
- Chorda tympani (chorda tympani) — carries taste fibers from the anterior 2/3 of the tongue and parasympathetic fibers to the salivary glands.
What are the anatomical features of the passage of the facial nerve in the temporal bone?
In the temporal bone, the facial nerve passes through the internal acoustic meatus and the facial canal. Anatomical features of its course include:
- Entrance — from the cranial cavity, the nerve heads toward the internal acoustic meatus.
- Passage — follows the facial (Fallopian) canal of the petrous part of the temporal bone (canalis n. facialis).
- Syntopy — in the canal, it joins the intermediate nerve, together forming the geniculate ganglion (ganglion geniculi).
- Relation to the canal — the facial nerve trunk occupies 70% of the cross-sectional area of the bony canal.
- Exit — leaves the canal and the cranial cavity through the stylomastoid foramen (foramen stylomastoideum) at the base of the skull.
For quick memorization of the key signs of facial nerve lesion, use the acronym ALBA: Asymmetry of the face, Lagophthalmos, Bell's phenomenon, Ageusia (loss of taste).
Class and exam questions
How to test the function of the motor portion of the nerve during an appointment?
Facial expression tests must be performed: ask the patient to wrinkle their forehead, close their eyes tightly, puff out their cheeks, bare their teeth, or whistle.
Why can middle ear inflammation lead to facial muscle paralysis?
During ear inflammation, edema occurs, which compresses the facial nerve trunk within the narrow facial canal of the petrous temporal bone, where the nerve initially occupies 70% of the area.
What is "lagophthalmos"?
This pathological condition (lagophthalmos) prevents the patient from fully closing the palpebral fissure on the affected side, which often leads to corneal dryness.
What else to study on this topic
- Technique of functional mimic tests in maxillofacial surgery.
- Surgical operations of dynamic and static suspension of facial tissues.
- Principles of facial nerve reinnervation (anastomoses with the hypoglossal and accessory nerves).
- Eagle syndrome and styloid process elongation.
- Topography and functions of the branches of the trigeminal nerve (I, II, III branches).
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Other topics in "Chapter 12. Diseases and Injuries of Facial Nerves (E.I. Deryabin)"
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