Facial Nerve Lesions: Clinical Distinction and Management

Clinical Presentation

The American Academy of Otolaryngology-Head and Neck Surgery recommends distinguishing UMN from LMN facial lesions based on forehead involvement, as LMN lesions affect the entire hemiface including forehead, while UMN lesions spare the forehead due to bilateral cortical innervation of the upper facial muscles 1
LMN pattern (peripheral facial palsy) is characterized by complete hemifacial weakness, including inability to wrinkle forehead, close eye, or smile on affected side, with loss of nasolabial fold and drooping of mouth corner 2
UMN pattern (central facial palsy) presents with forehead movement preserved, lower face weakness only, and often accompanied by contralateral limb weakness suggesting stroke 1

The American Academy of Otolaryngology-Head and Neck Surgery suggests that for isolated LMN facial palsy (Bell's palsy), imaging is not routinely indicated unless symptoms are atypical or recurrent, no improvement after 2-4 months, or other neurological signs are present 2, 3
The American College of Radiology recommends MRI as the preferred modality for evaluating facial nerve pathology, with pre- and post-contrast sequences, high-resolution thin-cut sequences, and coverage of brainstem, cerebellopontine angle, temporal bone segments, and parotid gland 4, 3
High-resolution temporal bone CT provides complementary information for osseous integrity of facial nerve canal, trauma or suspected fractures, and facial nerve canal dehiscence 3, 1

The American Academy of Otolaryngology-Head and Neck Surgery recommends oral corticosteroids (prednisone 1-1.5 mg/kg daily) within 72 hours of symptom onset as the standard of care for Bell's palsy, achieving 94% recovery rates 2, 1
Eye protection, including artificial tears, lubricating ointment, and eye taping, should be implemented immediately for patients with impaired eye closure to prevent exposure keratitis or corneal abrasion 2, 5
Surgical decompression may be considered for highly selected patients with complete paralysis, >90% ENoG amplitude reduction, absent EMG activity, and surgery within 3-14 days of onset 1
For UMN lesions (stroke/central causes), immediate stroke protocol management is required, with activation of stroke team for thrombolysis/thrombectomy evaluation and admission for comprehensive stroke workup and secondary prevention 1

The American College of Radiology suggests that for patients with perineural tumor spread, MRI is preferred for detecting perineural spread with thin-section protocol, while CT visualizes neural foramina expansion and FDG-PET/CT may be useful for localization and treatment response monitoring 4
The Lancet Diabetes and Endocrinology recommends performing thorough cranial nerve examination and laryngoscopy before and after head and neck surgery or radiotherapy, with evaluation of cranial nerves VII-XII systematically 6, 5