What is the role of imaging in the evaluation of the patient presenting with unilateral facial paralysis?
Year: 2017
Type: article
Abstract: Unilateral facial nerve paralysis can have numerous causes, but most cases are attributed to Bell palsy, a seemingly idiopathic, rapid-onset unilateral paralysis (usually occurring within 72 hours), with up to 90% of patients recovering spontaneously within 12 weeks.1, 2 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.2 Patients presenting with a unilateral facial paralysis most frequently are evaluated in the primary care or emergency setting, and misdiagnosis of presumed Bell palsy is common. Although Bell 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.1, 2 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.1, 3 Despite this, there is no consensus for when imaging is actually indicated.1 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. A retrospective study by Kinoshita et al. reviewed contrast-enhanced MRI findings of 147 patients with facial nerve paralysis (due to Bell palsy, Ramsay-Hunt syndrome, or trauma) compared to 300 control patients.3 The mean time interval between symptom onset and imaging was 15.4 days, with a maximum of 81 days. Patients with Bell palsy were found to have contrast enhancement of the distal meatal and labyrinthine segments of the facial nerve in 67% and 43% of cases compared to 0% of controls, as well as enhancement of the geniculate ganglion or tympanic-mastoid segments in 91% of cases compared to 21% of controls. Patients with Ramsey-Hunt syndrome displayed a similar pattern of enhancement. The authors suggested that this pattern is characteristic of acute inflammatory causes of facial nerve paralysis, confirming that MRI can be useful in diagnosing a classic Bell palsy, with implications for counseling patients, in addition to ruling out other etiologies. Boahene et al. described a series of 15 patients with facial paralysis and normal CT or MRI findings who were found to have neoplasms on histopathologic diagnosis.4 These patients shared the following associated factors, which prompted surgical exploration: progressive and prolonged paralysis (in 14 patients, time to total paralysis 2–21 months), facial pain, other cranial nerve involvement, and history of regional skin cancers. The authors presented an algorithm for further workup of unilateral facial nerve paralysis with negative clinical or imaging findings: stratify patients after six months as high or low risk based on the above associated factors, and repeat diagnostic evaluation for the high-risk group—with a low threshold for nerve biopsy if repeat testing is negative. Another retrospective case series describes the reasons for diagnostic delay in 13 patients initially diagnosed with Bell palsy who later were found to have alternate causes of facial paralysis.1 Twelve of the 13 patients had associated symptoms inconsistent with Bell palsy such as hearing loss, vertigo, and other cranial nerve involvement. Two patients had positive findings on CT or MRI that were reported incorrectly, and three patients had imaging that did not include all portions of the facial nerve. The authors proposed that appropriate imaging should be performed at three months after onset of acute facial palsy with partial to no recovery, and immediately in all patients with associated hearing loss or other neurological symptoms. Furthermore, imaging interpretation should be done by an experienced or specialized radiologist. Quesnel et al. presented an additional case series of four patients misdiagnosed with Bell palsy later found to have parotid neoplasms.5 All patients had initial imaging that was either incomplete (excluding the parotid, without contrast, or single modality) or incorrectly interpreted. This study also described an algorithm to reduce diagnostic delays in the event of an occult malignancy. Contrast-enhanced imaging with both CT and MRI is recommended at four months with no recovery from acute facial paralysis, even if prior imaging was negative, with repeat imaging at seven months if no lesions are identified. More recently, Hohman and Hadlock published a large retrospective review of 1,989 patients presenting with facial paralysis to a tertiary center, and proposed multiple algorithms for diagnosis and management.2 No imaging is included in the initial evaluation for acute-onset facial paralysis; in fact, the authors specifically do not recommend imaging for patients whose history is consistent with Bell palsy due to low yield. For insidious or progressive-onset facial paralysis with concern for malignancy, CT of the temporal bones and parotid bed is the first step, followed by MRI brain and IAC if CT is negative. If both CT and MRI findings are negative, imaging is repeated in six months. This same algorithm applies if there is no improvement in acute facial paralysis after six months. For recurrent segmental or unilateral facial palsy, MRI is the recommended first step. 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,3 and further work is needed to better understand the cost–benefit ratio of imaging as a diagnostic tool. Recommendations for when to image in the workup of unilateral facial paralysis are based on a retrospective review (level 2 evidence),2 a case-control study (level 3 evidence),3 and several case series (level 4 evidence).1, 4, 5
Source: The Laryngoscope
DOI: 10.1002/lary.26825
Authors: Brooke M. Su, Edward C. Kuan, Maie A. St. John
Institution: University of California, Los Angeles
Language: English
Subfield: Clinical Neurology
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2747966877