Central Versus Peripheral Facial Paralysis

The facial nerve can be damaged at any level along its course (Plate 1-27). Facial musculature paralysis is the hallmark of seventh cranial nerve lesions. The presence or absence of symptoms related to the various other components of the facial nerve are important for further localization. The patient with a peripheral facial nerve palsy, with the exception of an early very distal branch lesion within the parotid gland, has weakness of the entire ipsilateral side of their face, with asymmetric smile, inability to close the eye (orbicularis oculi), or wrinkle the forehead (frontalis). Intracranial, extramedullary lesions affecting the seventh nerve typically occur within the cerebellopontine (CP) angle, most commonly caused by large acoustic neuromas, and often involve the vestibulocochlear nerve. In these cases, diminished hearing, at times initially presenting with tinnitus, usually precede the onset of peripheral facial paresis. Rarely, very large tumors may also involve the ipsilateral trigeminal cranial nerve with accompanying unilateral facial anesthesia and loss of corneal reflex. A proximal pregeniculate, intracanicular facial nerve lesion characteristically also causes diminished lacrimation from greater petrosal nerve involvement, as well as hyperacusis (i.e., increased sensitivity to sound) due to associated stapedius muscle paresis. These lesions also lead to diminished salivation, absent or altered taste for the anterior two thirds of the tongue, and affected somatic sensation for the external auditory canal and mastoid area. Lesions between the geniculate ganglion and the stapedius nerve spare lacrimation, because the greater petrosal nerve has already exited. Damage between the branch points of the stapedius nerve and the chorda tympani results in hyperacusis and impaired salivation and taste, but not change in lacrimation. Lesions distal to the chorda tympani branch point result in pure ipsilateral facial weakness. Distal lesions that affect individual motor branches result in weakness that may be restricted to individual facial muscles.

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