Anatomy
Summary
Injuries to cranial nerve VII, or the facial nerve, can manifest as either central or peripheral facial palsy, each distinguished by its unique underlying lesions and clinical symptoms. In central facial palsy, an upper motor neuron lesion affects the contralateral lower muscles of the face while sparing the forehead. On the other hand, peripheral facial palsy results from a lower motor neuron lesion that causes ipsilateral facial weakness and affects the entire face, with no forehead sparing.
Various etiologies can lead to peripheral facial palsy. Bell's palsy is a common cause, characterized by acute-onset unilateral facial weakness, hyperacusis, and loss of taste sensation in the anterior two-thirds of the tongue. Other causes include parotid gland tumors, cerebellopontine angle tumors, vestibular schwannomas, Ramsay-Hunt syndrome (caused by the herpes zoster virus), sarcoidosis, and temporal bone fractures. Interestingly, stage 2 Lyme disease is also associated with peripheral facial palsy and presents a higher incidence of bilateral facial palsy.
Lesson Outline
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FAQs
Cranial nerve VII, also known as the facial nerve, is primarily responsible for a range of functions, including control of facial expressions, taste sensations from the anterior two-thirds of the tongue, and providing secretomotor function to the salivary glands (except the parotid gland) and the lacrimal gland.
Central facial palsy occurs due to a lesion at or above the level of the facial nucleus in the brainstem, affecting only the lower area of the face contralateral to the lesion and spares the forehead. Peripheral facial palsy is caused by a lower motor neuron lesion of the facial nerve itself, resulting in ipsilateral facial weakness involving the both the upper and lower parts of the face.
Bell's Palsy is a condition that causes sudden, unilateral, and severe facial weakness or paralysis, a result of inflammation of the facial nerve (CN III). While the exact cause is unknown, it is often associated with the Herpes simplex virus..
Parotid gland tumors and cerebellopontine angle tumors, such as vestibular schwannomas, can compress or invade the facial nerve, leading to facial palsy. The degree of facial dysfunction depends on the location and size of the tumor.
Conditions such as diabetes mellitus and Lyme disease can lead to inflammation and neuropathy, including the facial nerve. In diabetes, hyperglycemia can damage the facial nerve via glycosylation, whereas the bacteria Borrelia burgdorferi infects the facial nerve and can lead to facial weakness or paralysis in Lyme diseas.
