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Anatomy and Physiology

The facial nerve is a mixed nerve containing:

  1. Motor fibers from the motor nucleus within the pons to the posterior belly of the digastric muscle, stylohyoid muscle, stapedius muscle, and muscles of facial expression. Of note, the upper face receives bilateral central innervation; therefore, an upper motor neuron lesion will spare the upper face. A lower motor neuron lesion will involve the entire hemiface.

  2. Parasympathetic fibers arising from the superior salivary nucleus within the pons. Preganglionic, parasympathetic afferent fibers form following two nerves:

    1. Greater superficial petrosal nerve. Branches off the main trunk at the geniculate ganglion, synapses at the pterygopalatine ganglion, and provides input to lacrimal, nasal, and palatine glands.

    2. Chorda tympani nerve. Branches off the main trunk along the mastoid/vertical segment, joins the lingual nerve, synapses at the submandibular ganglion, and provides input to sublingual and submandibular glands.

  3. Special sensory afferent fibers travel in the lingual nerve to the chorda tympani nerve and provide taste to the anterior two-thirds of the tongue, and travel to the nucleus solitarius.

  4. Afferent fibers also provide sensation from the concha, external auditory canal, and earlobe.

The facial nerve is divided into following six segments:

  1. Intracranial segment (17-24 mm) from brain stem to internal auditory canal (IAC).

  2. Meatal segment (8-10 mm) from the fundus of the IAC, running in the anteriosuperior quadrant, to the meatal foramen.

  3. Labyrinthine segment (4 mm) from the meatal foramen to the geniculate ganglion. The meatal foramen is the narrowest segment of the intratemporal bony channel, and the nerve is most susceptible to inflammation at this point.

  4. Tympanic segment (11 mm) from the geniculate ganglion to the second genu.

  5. Mastoid/vertical segment (13 mm) from the second genu to the stylomastoid foramen.

  6. Extratemporal segment from the stylomastoid foramen, divides into the temporal, zygomatic, buccal, marginal mandibular, and cervical branches to innervate the muscles of facial expression.

Etiology of Facial Paralysis

There are hundreds of etiologies of facial paralysis with the most common causes being:

  1. Viral reactivation

  2. Lyme disease

  3. Trauma

  4. Postsurgical cases

  5. Benign or malignant tumors

The most common causes of synchronous, bilateral facial paralysis are

  1. Lyme disease

  2. Möbius syndrome

  3. Neurofibromatosis type 2

  4. Cavernous brain stem hemangioma and other brain stem pathologies

  5. Bilateral temporal bone fractures

  6. Guillain-Barré syndrome

  7. HIV

Assessment of Facial Paralysis

Assessment of facial paralysis begins with a detailed history and physical examination. The physical examination includes thorough head and neck examination with attention to otologic findings, cranial nerves, and palpation of the parotid gland and neck. In some cases, additional workup is required and may include laboratory testing, imaging, audiogram, and electrophysiologic testing.

Facial paralysis may be classified into flaccid facial paralysis (FFP), post-paralysis facial palsy (PPFP) characterized by hypertonicity and synkinesis, and mixed facial paralysis (MFP) with elements of flaccidity and ...

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