Treacher Collins Syndrome

Treacher Collins syndrome, also known as mandibulofacial dysostosis and Franceschetti-Zwahlen-Klein syndrome, has a distinctive facial appearance that is well known. This bilateral facial deformity has etiology in anomalies of the structures derived from the first branchial arch, groove, and pouch. The deformity is centered around the middle portion of the face as opposed to hemifacial microsomia, which is secondary to abnormalities of the first and second branchial arches and therefore usually centered around the lower face and mandible.

Treacher Collins syndrome is generally considered to be autosomal dominant in its inheritance with variable expressivity. The characteristic appearance revolves around the deformity in the lower lateral orbit and medial zygoma. There is frequently an absence of the bone in this region, which many think is consistent with a craniofacial cleft. However, the deformity extends outward from this area to the maxilla and mandible in such a way that it is much more severe than the malformation seen even in complex facial clefts. This suggests a more extensive underlying pathophysiologic process. Basic science animal investigation has produced similar malformations in animals with teratogenic doses of vitamin A and isotretinoin. The histologic findings demonstrated neurocrest development abnormalities.

The maxilla, from the nasomaxillary region, is caudally rotated. This results in clockwise rotation of the mandible, which is also retrognathic and micrognathic. These abnormalities in the facial skeletal framework displace the associated soft tissues, resulting in many other deformities. The palpebral fissures are short and slanted downward. The lateral canthus is inferiorly displaced, and there is usually an associated coloboma of the lower eyelid. The nose has a parrot beak deformity made more noticeable by its small size. The underlying nasal, oral, and pharyngeal airway is narrowed and compromised, resulting in airway obstruction and the need for a tracheostomy in patients with more severe disease. Other malformations include cleft palate in 35% of patients and macrostomia in 15%. Finally, there frequently are auricular abnormalities that are both internal and external in nature. Because the ear anomaly is bilateral, most patients require a bone conduction hearing aid. Cochlear hearing devices that are anchored to bone have been introduced. The patient usually undergoes costochondral external ear reconstructions for complete microtia.

Nager syndrome is similar to Treacher Collins syndrome but with hypoplastic or absent thumbs, radius and ulna fusion, or radial and metacarpal hypoplasia or aplasia. Other aspects in the differential diagnosis of Nager syndrome are a lower incidence of coloboma, a higher incidence of cleft palate, and more severe hypoplasia of the mandible.