Introduction
Iatrogenic facial nerve palsy is a concern to the patient and clinician. Not only is the
deformity aesthetically distressing but can also be functionally problematic in terms of oral competence, lip trauma and speech1; such injuries are a source of litigation.
Marginal mandibular nerve (MMN) palsy, results in an asymmetrical smile. The MMN is at particular risk during procedures such as rhytidoplasties, mandibular fractures, neck dissections and salivary gland surgery1,2. Cited causes for high incidence of MMN palsies are large anatomical variations, exposed course, and tumour grade and node involvement dictating nerve sacrifice.
An alternative cause for post-operative asymmetry is platysma dysfunction caused by damage to the cervical branch of the facial nerve, or direct division of platysma. This usually follows a transient course and tends to recover well. Nerve injury can be of multiple aetiologies: transaction, thermal injury, or retraction, therefore the severity can range from neuropraxia to neurotemesis, complicating the picture. The distinction between MMN palsy and palsy of the cervical branch otherwise termed ‘Pseudo-paralysis of the mandibular branch of the facial nerve’2 should therefore be made.
Despite the academic recognition of pseudo-palsies of the MMN, this differentiation is often not emphasised in clinical practice. Establishing the true cause of post-operative smile asymmetry is key to advise the patient on recovery and protect against litigation. This review illustrates the anatomical and clinical considerations when assessing post-operative smile asymmetry.