Imaging traumatic facial nerve injuries: a narrative review of current strategies and future directions for cranial nerve imaging

Traumatic facial nerve injuries can result in temporary or permanent loss of function. Restoration of facial expression may occur spontaneously or require surgical intervention. Although thorough examination and history can localize the site of facial nerve damage, it can be difficult to predict if and when recovery will occur. This is salient because the window for optimal outcomes from surgical re-neurotization can be as short as 1 to 2 years, after which functional loss may be irreversible. It is essential to offer patients the most appropriate treatment plan based on prognosis, and imaging plays an essential role in localizing the site and morphology of nerve injury. Multiple imaging modalities have been used to evaluate the facial nerve, including computed tomography (CT) and, more recently, advanced magnetic resonance imaging (MRI) and ultrasound (US). CT and MRI are more commonly implemented; however, Diffusion tensor tractography, high-resolution US, and functional US are gaining traction for studying cranial nerve pathology. Until recently, the morphology of facial nerve and other cranial nerve injuries could only be inferred using non-invasive diagnostic techniques. With the advent of newer imaging technologies and techniques to examine nerves, more refined assessment and prognostic information is now possible. This article reviews up-to-date cranial nerve imaging techniques from the last ten years and explores future avenues for facial nerve imaging.