Metopic Synostosis (Trigonocephaly)
What is Metopic Synostosis?
Metopic craniosynostosis is the second most common form of craniosynostosis comprising approximately 20-25 percent of all cases of craniosynostosis. The metopic suture is vertically oriented in the center of the forehead (see the figure below). The metopic suture responds to brain growth by producing bone in the frontal bone that adds width to the forehead. The metopic suture is the only suture in the skull that normally fuses, typically between 3 and 9 months of age. When the metopic suture closes earlier than 3-9 months of age it is called metopic craniosynostosis. When the metopic suture closes early the frontal bone and forehead cannot grow in response to the growth of the brain. The head shape that results from the closure of this suture is called trigonocephaly, because of the triangular shape of the skull with an abnormally pointed, narrow forehead and wide, flat back of the skull.
The severity of head shape and appearance changes in metopic craniosynostosis ranges from mild narrowing of the forehead with a prominent ridge in the center of the forehead to the most severe form with a severely pointed forehead. The common features found in patients with severe metopic synostosis include:
• A triangular head shape when looking down on the top of the head
• A narrow forehead with a noticeable ridge in the midline
• Deformation of the upper portion of the eye sockets
• Eyes that are too close to each other, with eyelid folds that cover the inside corners of the eyes (epicanthal folds)
What is a Benign Metopic Ridge?
It is important to distinguish a benign metopic ridge from true metopic craniosynostosis. The metopic suture normally closes between 3-9 months of age. This is called physiologic closure of the suture because it is supposed to happen. When the metopic suture closes earlier than 3-9 months, metopic craniosynostosis may be present. It is normal for the metopic suture to thicken to some degree as it closes. Occasionally as the metopic the suture undergoes normal closure it can thicken to a degree where it is visible and palpable to the touch. When this ridging occurs in the normal time frame and the head shape is otherwise normal it is called a benign metopic ridge. This is a normal finding and does not require any treatment.
The presence of a benign metopic ridge can sometimes be concerning to parents and pediatricians because they may have difficulty differentiating between a benign metopic ridge and the sutural ridging that accompanies metopic craniosynostosis. If the head shape is normal and the ridging of the metopic suture began between 3-9 months of age, the diagnosis is almost certainly a benign metopic ridge. If you still have concerns you should be seen by a craniofacial surgeon.
How and Why Do We Treat Metopic Synostosis?
In clear cut cases of severe disease, the concerns for elevated pressure that can occur in the skull (about 15%) and the appearance issues that will result from the deformity make the decision to operate easier to make. For those patients with moderate severity, you will have to discuss the functional and appearance issues with the surgeon to determine the appropriate treatment for your child.
Metopic craniosynostosis can be treated with either strip craniectomy with use of molding helmet after surgery or fronto-orbital advancement, depending on the deformity. The goal of treatment is to restore a normal contour to the forehead and upper portion of the eye sockets. I treat metopic craniosynostosis with fronto-orbital advancement (FOA) because this provides a more predictable correction to improve the contour of the forehead and upper portion of the eye sockets. This procedure is done at 9-12 months of age. Read more about fronto-orbital advancement.