It then traverses the cerebellopontine angle in its cisternal segment, enters the internal auditory canal within its meatal segment, and courses through the temporal bone (which includes the labyrinthine, tympanic, mastoid segments, and geniculate ganglion). The facial nerve exits the temporal bone at the stylomastoid foramen, and the extracranial segment courses through the parotid gland. Peripheral, nuclear, or infranuclear facial nerve paralysis presents as ipsilateral facial paralysis with involvement of the forehead (which is usually spared with a supranuclear facial nerve palsy) and can result from pathology affecting the facial nerve nucleus or any portion of the facial nerve after exiting the brainstem within its intracranial and extracranial segments. Within the pons, the facial nuclei can be affected by intra-axial conditions such as infarction, vascular malformations, tumors, and multiple sclerosis. Brainstem lesions are often accompanied by additional neurologic symptoms that can help localize the lesion clinically [102,103]. Rarely brainstem or cortical infarct can result in an isolated facial nerve palsy [102,103]. As the facial nerve exits the brainstem and courses within the cerebellopontine angle, the internal auditory canal, and through the temporal bone, it may be affected by facial and vestibular schwannomas, meningiomas, vascular lesions, inflammation, cholesteatomas, paragangliomas, epidermoid cysts, trauma, and intrinsic bone tumors. The extracranial facial nerve may be affected by inflammation, parotid tumors, conditions of the neighboring anatomic spaces, and skull base pathology including carcinomas, sarcomas, trauma, and inflammatory disease [99,102]. Perineural spread of a tumor can result in facial nerve palsy and is discussed in Variant 10 [104]. Facial nerve palsy can present with facial droop, pain around the jaw or ear, hyperacusis, tinnitus, reduced taste, and decreased lacrimation or salivation.
Cranial Neuropathy. It then traverses the cerebellopontine angle in its cisternal segment, enters the internal auditory canal within its meatal segment, and courses through the temporal bone (which includes the labyrinthine, tympanic, mastoid segments, and geniculate ganglion). The facial nerve exits the temporal bone at the stylomastoid foramen, and the extracranial segment courses through the parotid gland. Peripheral, nuclear, or infranuclear facial nerve paralysis presents as ipsilateral facial paralysis with involvement of the forehead (which is usually spared with a supranuclear facial nerve palsy) and can result from pathology affecting the facial nerve nucleus or any portion of the facial nerve after exiting the brainstem within its intracranial and extracranial segments. Within the pons, the facial nuclei can be affected by intra-axial conditions such as infarction, vascular malformations, tumors, and multiple sclerosis. Brainstem lesions are often accompanied by additional neurologic symptoms that can help localize the lesion clinically [102,103]. Rarely brainstem or cortical infarct can result in an isolated facial nerve palsy [102,103]. As the facial nerve exits the brainstem and courses within the cerebellopontine angle, the internal auditory canal, and through the temporal bone, it may be affected by facial and vestibular schwannomas, meningiomas, vascular lesions, inflammation, cholesteatomas, paragangliomas, epidermoid cysts, trauma, and intrinsic bone tumors. The extracranial facial nerve may be affected by inflammation, parotid tumors, conditions of the neighboring anatomic spaces, and skull base pathology including carcinomas, sarcomas, trauma, and inflammatory disease [99,102]. Perineural spread of a tumor can result in facial nerve palsy and is discussed in Variant 10 [104]. Facial nerve palsy can present with facial droop, pain around the jaw or ear, hyperacusis, tinnitus, reduced taste, and decreased lacrimation or salivation.