There are two coronal coronal sutures, left and right. Either coronal suture may close prematurely. Closure of a single coronal suture is called unilateral coronal craniosynostosis or unicoronal craniosynostosis. When both coronal sutures close prematurely it is call bilateral coronal craniosynostosis or bicoronal craniosynostosis.
Unilateral Coronal Synostosis (Plagiocephaly)
Unilateral coronal craniosynostosis is present when one coronal suture closes before growth of the brain and skull are complete. This represents about 15% of all cases of isolated craniosynostosis. The brain continues to grow at the same rate whether one or more cranial sutures close prematurely. When one coronal suture closes prematurely the remaining cranial sutures must compensate with increased growth to continue to accommodate the growth of the brain. This growth pattern causes a very uneven appearance to the skull and face because there is reduced growth on one side of the skull and excessive (compensatory) growth on the opposite side of the skull.
These patients have flat foreheads and raised eye sockets on the side of the closed coronal suture. On the side with the open coronal suture, the forehead is pushed forward and the upper part of the eye socket is pushed downward. Additional findings include deviation of the nasal bridge toward the side of the closed coronal suture and deviation of the chin away from the closed suture. If the left coronal suture is closed, the neighboring sutures including the right coronal suture must grow faster to make space for the brain. This is what causes the abnormal shape of the head.
Unilateral synostosis is treated with a fronto-orbital advancement at age 9-12 months of age. The goal of this procedure is to correct the position of the upper portion of the eye socket and forehead. Read more about fronto-orbital advancement. In order to have an even appearance when fully grown, we must overcorrect the forehead and eye socket position in a more forward position than the unaffected side. The children grow into the overcorrection in 1-2 years. If the forehead and upper eye socket are not overcorrected, the face and skull will have an uneven appearance when the child is fully grown. See before and after photos of patients with unicoronal craniosynostosis who were treated with fronto-orbital advancement.
Bilateral Coronal Synostosis (Brachycephaly)
Non-syndromic bilateral coronal craniosynostosis is rare, making up only 5-10% of all isolated craniosynostosis. In these patients both coronal sutures are closed which creates a symmetric change in the shape of the skull, unlike unilateral coronal synostosis which causes a very uneven appearance of the skull. Because the coronal sutures normally grow forward and are now closed the skull is shorter from front to back. The remaining open sutures must make up for the loss of growth at the closed coronal sutures. The compensatory overgrowth at the remaining open sutures causes the skull to be abnormally tall and wide. This skull shape that is tall, wide and short from front to back is called brachycephaly. The back of the head is also flattened. Note that the upper portion of the eye sockets (orbits) are abnormally raised and push back. The forehead is very flat and wide.
Similar to unilateral coronal synostosis, these patients will eventually require a fronto-orbital advancement (FOA) in order to achieve a normal appearance to the forehead and eye sockets. In bilateral coronal synostosis there are two sutures involved. Since two sutures are involved the changes in the skull shape are more profound than unilateral synostosis. The shape of both the front and back of the skull are severely affected. Read more about front-orbital advancement.
Recently, posterior cranial vault distraction osteogenesis (PVDO) has emerged as a powerful procedure in these patients. Distraction osteogenesis (DO) is a technique in which cuts are made in the facial or skull bones and specialized devices (distractors) move the cut bones slowly over time. This creates new bone and allows for repositioning of the bones also. PVDO uses specialized devices called cranial distractors to move the bones of the back of the skull very slowly. PVDO allows for reshaping and enlargement of the back of the skull, generation of new bone and also slowly stretches the scalp as the bones move. The scalp is usually what limits how much we can correct the head shape in a single operation. Cranial distraction allows for more significant reshaping of the skull than single stage procedures can provide. Expanding the back of the head creates space for the growing brain and allows us to delay the reshaping of the forehead and eye sockets with FOA to an age closer to the completion of skull growth. If the FOA procedure can be delayed to a later age the long-term appearance of the patients is better.
I have published several articles on PVDO and presented my research on PVDO at both national and international meetings (see my publications). Before and after photos of one of my patient can be seen below. The photos show the changes in the head shape achieved with PVDO performed at age 6 months and FOA performed at age 3 years old.