Need for Routine Brain Magnetic Resonance Imaging for Unilateral Facial Palsy in Emergency Department

Objectives: The need for routine brain magnetic resonance imaging (MRI) for patients presenting with unilateral facial palsy in the emergency department (ED) is a subject of ongoing debate. This study aimed to evaluate the diagnostic yield of MRI in this population and to identify clinical risk factors associated with non-idiopathic causes, to inform selective imaging strategies. Methods: This single-center, retrospective study was conducted in the ED of a tertiary-care center in Korea. We analyzed adult patients (aged ≥ 18 years) who presented with facial palsy as the primary symptom between 1 January 2020 and 31 December 2022. Patients with other neurological abnormalities detected during the initial examination or those who did not undergo brain MRI were excluded. The primary outcome was the identification of positive MRI findings, defined as brain lesions (e.g., ischemic stroke, tumor, and hemorrhage) considered causally related to the facial palsy based on anatomical correlation and radiological interpretation. Patients were categorized into positive or negative MRI groups accordingly, and baseline characteristics were compared between the groups. Results: Among the 436 patients who underwent brain MRI, 13 (3.0%) showed positive findings such as brain tumors or stroke that led to diagnoses other than Bell's palsy, while the remaining 423 (97.0%) were ultimately diagnosed with Bell's palsy. The proportion of patients with a history of transient ischemic attack/stroke and malignancy was significantly higher in the group with non-idiopathic facial palsy (p = 0.02 and p < 0.001, respectively). Conclusions: In adults presenting to the ED with clinically isolated unilateral facial palsy and no other neurological signs, routine brain MRI had a low diagnostic yield (3%). A history of malignancy or prior TIA/stroke was associated with alternative diagnoses. A selective imaging strategy based on risk factors may improve diagnostic efficiency without compromising safety.