The isolated paresis of the marginal mandibular branch of the facial nerve: Clinical appearance, causes, diagnosis, and therapy. An overview

Background: Disorders of lower lip in facial expression are mostly caused by functional impairment of the marginal mandibular branch of the facial nerve. In a typical case, active exposure of the incisors of the mandible is not possible and the lip appears distorted towards the healthy side. The most frequent cause of a lesion of the marginal mandibular branch is iatrogenic injury during operations in the mandibular or parotid region. Differential diagnosis: Functional disorders of the platysma, congenital hypoplasia or aplasia of the lower lip muscles, and defective healing following facial palsy may lead to a similar disorder which, however, must be differentiated from an isolated paralysis of the marginal mandibular branch. Treatment: In addition to inactivation of the nerve branch on the opposite side, several surgical procedures have been described to achieve not only aesthetic, but also functional rehabilitation of lower lip expression. The present review gives an overview on the causes, clinical appearance, diagnosis, differential diagnosis, and therapy of unilateral isolated paresis of the marginal mandibular branch of the facial nerve.