Incidence of Underlying Abnormal Findings on Routine Magnetic Resonance Imaging for Bell Palsy

Abstract

Importance: There is no consensus on the benefits of routine magnetic resonance imaging (MRI) of the facial nerve in patients with suspected idiopathic peripheral facial palsy (PFP) (ie, Bell palsy [BP]).

Objectives: To estimate the proportion of adult patients in whom MRI led to correction of an initial clinical diagnosis of BP; to determine the proportion of patients with confirmed BP who had MRI evidence of facial nerve neuritis without secondary lesions; and to identify factors associated with secondary (nonidiopathic) PFP at initial presentation and 1 month later.

Design, setting, and participants: This retrospective multicenter cohort study analyzed the clinical and radiological data of 120 patients initially diagnosed with suspected BP from January 1, 2018, to April 30, 2022, at the emergency department of 3 tertiary referral centers in France.

Interventions: All patients screened for clinically suspected BP underwent an MRI of the entire facial nerve with a double-blind reading of all images.

Main outcomes and measures: The proportion of patients in whom MRI led to a correction of the initial diagnosis of BP (any condition other than BP, including potentially life-threating conditions) and results of contrast enhancement of the facial nerve were described.

Results: Among the 120 patients initially diagnosed with suspected BP, 64 (53.3%) were men, and the mean (SD) age was 51 (18) years. Magnetic resonance imaging of the facial nerve led to a correction of the diagnosis in 8 patients (6.7%); among them, potentially life-threatening conditions that required changes in treatment were identified in 3 (37.5%). The MRI confirmed the diagnosis of BP in 112 patients (93.3%), among whom 106 (94.6%) showed evidence of facial nerve neuritis on the affected side (hypersignal on gadolinium-enhanced T1-weighted images). This was the only objective sign confirming the idiopathic nature of PFP.

Conclusions and relevance: These preliminary results suggest the added value of the routine use of facial nerve MRI in suspected cases of BP. Multicentered international prospective studies should be organized to confirm these results.

Figure 1.. Study Flowchart

BP indicates Bell palsy; MRI, magnetic resonance imaging.

Figure 2.. Magnetic Resonance Imaging of Patients With Peripheral Facial Palsy Due to Cerebral Lymphoma and Multiple Sclerosis

A, Contrast-enhanced T1-weighted image in a patient in their 50s with right peripheral facial palsy (PFP) due to cerebral lymphoma showing right cerebellopontine angle lesion merging with the acoustic-facial bundle with enhancement after gadolinium injection. B, Contrast-enhanced T1-weighted image in the same patient showing other hypertense brain lesions. C, Multiple areas of white matter hyperintensity in a woman in her 20s with left PFP due to multiple sclerosis. D, Fluid-attenuated inversion recovery image in the same patient showing hyperintensity of the protuberance, seemingly in the root of the acoustic-facial bundle (arrowhead).

Figure 3.. Magnetic Resonance Imaging of Patients With Peripheral Facial Palsy (PFP) Due to Facial Nerve Schwannoma and Facial Nerve Hemangioma

A, Contrast-enhanced T1-weighted image in a patient in their 50s with right PFP due to facial nerve schwannoma showing well-defined nodular contrast in the labyrinthine portion of the right facial nerve (arrowhead). B, Nodular T2 hypointensity in the fundus of the internal auditory canal (arrowhead) in the same patient. C, T1 isointense lesion centered on the lateral part of the geniculate ganglion (arrowhead) in a patient in their 40s with left PFP due to facial nerve hemangioma. D, Intense heterogeneous enhancement after gadolinium injection (arrowhead) in the same patient. E, T2 hypointensity (asterisk) in the same patient.

Figure 4.. Magnetic Resonance Images of a Patient in Their 40s With Right Idiopathic Peripheral Facial Palsy

Images were obtained 5 weeks after presentation to the emergency department, showing typical signs of right facial nerve neuritis. Left arrowheads indicate increased hyperintensity after gadolinium injection; right arrowheads indicate the left facial nerve for comparison. IAC indicates internal auditory canal.