Hemifacial Microsomia (Craniofacial Microsomia)
Hemifacial microsomia, also called craniofacial microsomia, is a condition where one or both side of the face have underdeveloped growth of the bone and soft tissues. This is a common condition affecting approximately 1 in 5,600 newborns. The features of hemifacial microsomia can vary in their severity and structures affected. There are several features that are reliably found and are detailed in the acronym OMENS that we use when evaluating patients:
· Orbital dystopia – abnormal position of the eye socket on the affected side
· Mandibular hypoplasia – underdeveloped lower jaw
· Ear abnormalities – typically there is a rudimentary external ear (microtia)
· Nerve function – the nerves that move the facial muscle may not function
· Soft tissue deficiency – decreased bulk in the muscle and fat of the cheek
Usually the orbital changes are not severe enough to require surgical correction.
Mandibular hypoplasia means that the lower jaw is smaller than normal on one or both sides. Hemifacial microsomia most commonly affects one side of the face. On one side, the lower jaw is smaller on side which causes the chin to move away from the middle toward the smaller side. This causes the jawline and face to look uneven. The smaller size of the lower jaw also causes the bite to be tilted up on the small side. There is a grading system to define the severity of the size discrepancy of the jaw.
Treatment depends on the severity of the hypoplasia. If mild, no surgery or corrective surgery when the child is fully grown will be needed. In more severe cases, a procedure to lengthen the lower jaw is required. There are two main approaches to lengthening the lower jaw. The jaw can be lengthened with a procedure call distraction osteogenesis in which the jaw bones are cut and new bone is generated using specialized devices. The lower jaw can also be made bigger by borrowing bone (grafting) taken from the ribs or lower leg. The goal of both treatments is to restore normal dimensions to the jaw and face and normalize the dental occlusion (bite).
The ear abnormalities can vary from no abnormality to a completely absent ear. Microtia is the term used to describe severe malformations of the ear where the ear is smaller than normal and severely misshapen. Read more about microtia and its treatment.
The facial nerve is the nerve that powers movement of the facial muscles. About 15-30% of children hemifacial microsomia will have some weakness or paralysis of some or all of the facial muscles on the affected side.
The soft tissue deficiency of the face causes the cheek to look deflated compared to the unaffected side. There are several ways to treat this deficiency. I most commonly perform fat grafting where I borrow fat from the flanks or abdomen and inject it into the areas of deficiency. This can be performed at various ages depending on the treatment plan for treating the small lower jaw.