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Explore This IssueJuly 2018
Unilateral facial nerve paralysis can have numerous causes, but most cases are attributed to Bell’s palsy, a seemingly idiopathic, rapid-onset unilateral paralysis (usually occurring within 72 hours), with up to 90% of patients recovering spontaneously within 12 weeks. In the management of facial paralysis due to trauma, infection, or neoplastic origin, making a timely diagnosis is crucial for addressing the underlying cause, with a possible secondary goal of restoring nerve function. Patients presenting with a unilateral facial paralysis most frequently are evaluated in the primary care or emergency setting, and misdiagnosis of presumed Bell’s palsy is common. Although Bell’s palsy has a classic presentation readily identified with a thorough history and physical exam, it remains a diagnosis of exclusion after other potential causes are ruled out.
Imaging has been described as a sensitive method for distinguishing among etiologies of unilateral facial paralysis. Specifically, gadolinium-enhanced magnetic resonance imaging (MRI) is the modality of choice for lesions located within the parotid gland, cerebellopontine angle, and internal auditory canal (IAC), whereas high-resolution computed tomography (CT) is preferred for temporal bone pathology.
Despite this, there is no consensus for when imaging is actually indicated. Moreover, imaging is not without risk (e.g., contrast-induced side effects) and may carry significant healthcare costs, although to date there have been no studies examining the cost effectiveness of imaging in the diagnosis of facial paralysis. This review aims to determine when it is appropriate to use imaging in the workup of unilateral facial paralysis, and which modality would be most useful for further management.
Imaging is indicated in the initial evaluation of unilateral facial paralysis in the presence of symptoms inconsistent with Bell’s palsy, such as slow, progressive onset of paralysis or multiple cranial nerve involvement, and also at three to six months after onset if there are no signs of recovery. Choice of CT or MRI should depend on symptoms, clinical concern, and availability of resources. Although MRI can identify a wider range of pathologies and should likely be first-line, CT often is faster and more readily available. Intratemporal causes of facial paralysis can be evaluated with either modality, with CT more often utilized for surgical planning. Imaging is best done with contrast enhancement for either modality, should include all portions of the facial nerve, and ideally should be interpreted by a radiologist with specialization in head and neck imaging. However, current imaging techniques are unable to provide prognostic information for management of facial paralysis, and further work is needed to better understand the cost–benefit ratio of imaging as a diagnostic tool (Laryngoscope. 2018;128:297–298).