The human skull is separated into several plates with openings (sutures) between them. These sutures are made up of fibrous tissue that eventually fuses into bone later in life. These openings allow the baby's skull to adjust to the birth canal during delivery and provide space for the baby's rapidly growing brain. Some of these sutures naturally fuse into bone in the first year of life, while others stay open for many years. When the sutures fuse into bone too early, you have what is called craniosynostosis. The brain continues to grow, but causes the skull to take on an atypical shape that varies based on which sutures have closed. Premature fusion can also cause increased pressure inside of the head which needs to be corrected with surgery. You can see in the image below the various shapes the skull can take when each of the sutures fuse:
Craniosynostosis on its own is not a terribly rare finding in infants. The statistics I've run into vary a bit, but approximately 1 in every 2,000 babies has some form of craniosynostosis. 80-90% of these cases are isolated, meaning the only presenting abnormality is the suture fusion and resulting skull shape. Most of these cases only involve the fusion of one suture (i.e. just the sagittal, one coronal, etc) . This type of craniosynostosis usually only requires skull surgery to open the suture back up and allow for the brain to expand normally. There isn't a lot of information out there on why isolated craniosynostosis occurs.
The other 10-20% of craniosynostosis cases are syndromic, meaning there is a genetic syndrome at play as well as the suture fusion (e.g. Crouzons, Apert, Pfeiffer, Saethre-Chotzen, etc...). When there are multiple sutures that have fused prematurely, it is likely a case of syndromic craniosynostosis. These syndromes vary widely in presentation and implication. Most of them have distinct physical characteristics, but while some syndromes have potentially no effect on development or lifespan, others have many. Most craniosynostosis syndromes are considered autosomal dominant (only one parent has to be a carrier for them to present themselves in a child), but can also occur spontaneously (with no family history). Syndromic cases often require multiple surgeries (which are generally started earlier than non-syndromic cases) in order to relieve intracranial pressure, as well as remedy some of the other presenting issues dependent on that syndrome. Depending on the type and severity of the syndrome, additional therapies may be necessary to assist in development.
There are a couple of different kinds of surgery that are done to correct craniosynostosis. When the fusion is detected early enough and there aren't multiple sutures involved, an endoscopic procedure can be performed. This is a less invasive surgery that is done between 3-6 months of age and requires the use of a helmet following surgery to ensure that the skull reforms properly. Once a baby has passed the 6 month mark, or in more complex cases, a surgery called CVR (cranial/calvarial vault remodeling) is done. Both are for the purpose of reopening the fused suture(s) to allow for brain growth.
This video from Boston Children's Hospital gives a basic explanation of craniosynostosis and the surgeries done. For more information, I recommend checking out http://cappskids.org and http://www.ccakids.org
Now, for our Aberdeen:
Based on our ultrasounds and the fetal MRI, we are looking at the fusion of 3 sutures (both coronal sutures and the sagittal suture). This, and a growing list of other markers (shortened limbs, pyelectasis, ventriculomegaly, etc...), indicate that she probably has syndromic craniosynostosis. The only way to diagnose these syndromes in-utero is through amniocentesis. There are some risks involved with invasive tests like amniocentesis, so (like we did back when we were talking about Down Syndrome) we opted to forego a prenatal diagnosis. As a result, we do not know which syndrome (if any) Abby will have. After Abby is born, we will meet with the geneticist from Dayton Children's Hospital in order to carry out the tests necessary to make a diagnosis and formulate a treatment plan. Like other conditions, there is a spectrum involved with the symptoms of syndromic craniosynostosis. Even with a diagnosis, we really won't know what Abby's life will be like, but hopefully we'll be able to give her the best start we can!
We've still got a lot of learning to do, but hopefully that provides a clearer idea of where we are at this point in our journey!