Moebius syndrome: the new finding of hypertrophy of the coronoid process

The first detailed description of congenital facial paralysis was reported by Moebius in 1888. It is characterized by either unilateral or bilateral paralysis of the facial muscles and an associated abducens palsy. The present report is of two patients with Moebius syndrome, who were also diagnosed with trismus at birth. Each patient also demonstrated bilateral hypertrophy of the coronoid process of the mandible. In effect, the zygoma obstructed the excursion of the mandible because of a "coronoid block." A three-dimensional computed tomography scan demonstrated normal temporomandibular joints but bilateral hypertrophy of the coronoid processes and micrognathia. Both patients demonstrated less than 10 mm of oral excursion. Bilateral coronoidectomies were performed through an intraoral approach. The oral excursions after surgery increased to at least 20 mm. In each of these patients, the coronoid process was enlarged relative to the zygoma, which was of normal size and configuration. The trismus was associated with blocking of the coronoid by the anterior zygoma, preventing open or full excursion of the hypoplastic mandibles. Moebius syndrome can have a variable presentation at birth. In two patients, the authors describe a new finding of hypertrophy of the coronoid process and trismus secondary to obstruction of the coronoid by the hypertrophic zygomas during oral excursions. Each patient is described, and a review of the literature is discussed.