Bell Palsy Mimics on CT and MRI

Idiopathic facial nerve paralysis, commonly referred to as Bell palsy, accounts for most cases of peripheral facial nerve palsy. It is thought to relate to reactivation of the herpes simplex virus, and it is typically characterized by acute-onset, self-resolving facial paralysis that lasts 3–6 weeks. Although routine imaging often is not indicated for the classic presentation of Bell palsy, atypical clinical features, such as lack of recovery, malignancy history, and recurrent episodes, should prompt workup for alternative causes of facial nerve paralysis. If imaging is performed, which typically includes MRI, asymmetric linear enhancement of the facial nerve on the affected side supports a diagnosis of idiopathic facial paralysis. However, one of the major roles of imaging is to identify causes of Bell palsy mimics. In this Case-Based Review, we review the imaging features of alternative causes of facial nerve paralysis.