The Craniofacial Team of Texas specializes in the diagnosis and treatment of craniosynostosis. Craniosynostosis (from cranio meaning skull, syn meaning together, and ostosis relating to bone) is a condition in which an infant’s skull bones prematurely fuse, thereby changing the growth and shape of the skull. This may result in increased intracranial pressure leading possibly to visual impairment, sleeping impairment, eating difficulties, or an impairment in development.
Normal Skull Anatomy and Physiology
It is important to have an understanding of skull anatomy and growth before we jump into the understanding of craniosynostosis. The skull is comprised of a number of bone plates that relate to each other through specialized joints called “cranial sutures”. Although there are several major and minor sutures, the sutures that potentially have the most clinical significance are the singular metopic and sagittal sutures, as well as the paired (right and left) coronal and lambdoid sutures.
Cranial sutures are very unique and specialized joints (syndesmosis joints). Their primary purpose is to grow bone in response to the rapidly developing brain within the protective skull compartment (cranial cavity or calvarium). The skull not only needs to be firm to protect the brain from accidental blows, but should also be expansile to accommodate its rapid growth. The brain doubles in volume in the first year of life and almost triples in volume by the age of three. The sutures of the skull allow for this important but almost contradictory balance of protection and growth. A quick look at head circumference growth curve of children shows the rapid growth of the brain in years 1 and 2 very well:
The steepness of the curve from 0 to 14 months of age is primarily related to the increase in brain volume (brain growth). The size of a child’s brain typically reaches 80% of adult size by the age of 2. The growth in head circumference after that age is more related to growth in the thickness of the skull and scalp but not actual brain growth. “Hat size” increases but not necessarily “brain size”.
The health, development, and protection of your child’s brain are the most important factors that influence our treatment strategies. These strategies are protocol driven and based upon the team’s consensus opinion of the most relevant clinical evidence available.
Do cranial sutures stay open our entire lives?
No. The various sutures close at different ages. The metopic suture closes earliest, around 6 months to 2 years. The rest of the sutures stay open into our 20’s and 30’s. The brain and fluid cavities of the brain do continue to grow in volume as we go into early adulthood, albeit not nearly as rapidly as the first couple years of life. Since the skull is much firmer (calcified or “rock-like”) and thicker, the skull needs the sutures to grow bone for any increase in volume.
Interestingly, there is a lot of variability here. We have operated on adults in their 30’s for reasons unrelated to their skull sutures and have coincidentally found open metopic sutures. We have also seen young adults with closed coronal, lambdoid, and sagittal sutures, but with normal head shapes and, often, no indication or symptoms of high pressure.
What is craniosynostosis?
Simply, it is early, abnormal fusion of a cranial suture or sutures (joints between the bone plates). As stated earlier, most sutures fuse when a person is 20-30 years of age, with the exception being the metopic suture fusing around 6 months to 2 years. Theoretically, a person can suffer consequences of an early skull suture fusion no matter what age it fuses. However, we usually see the most severe consequences when the fusion happens early in life, often before birth.
We learned that a suture’s purpose is to grow bone to accommodate a growing brain, and that most brain growth occurs in the first two years of life. The brain reaches 85% of adult size by age 3 years (see brain size vs. age diagram).
So it makes sense that the sutures are vitally important in the first two years of life. The earlier the fusion, the more severe the restriction in growth and, consequently, volume provided to the brain.
Does the exact time a suture prematurely fuses affect my child?
Yes. Because of the rapid brain growth in the first two years of life, the brain really relies on the sutures to grow the skull during this period. So the earlier in pregnancy the suture fuses, the greater the restriction. Clinically, this is seen as a more severe change in the shape of the head with earlier fusions. For example, a patient with a sagittal suture fusion that occurs in the second trimester of pregnancy will have a much more “scaphocephalic” skull than a patient that has a fusion occur at 6 months after birth. The earlier fusion will have a more significant effect on head shape compared to a later fusion that may produce a relatively normal appearing skull. There is a correlation with the degree of deformity and the restriction in volume. Consequently, the more severe restriction leads to a more severe increase in pressure that the brain experiences. So it follows that the earlier the fusion, the more likely a patient is to experience abnormally increased intracranial pressure earlier in life. There is not a lot of longitudinal data demonstrating this primarily because most kids showing increased intracranial pressure are operated early in life. We do, however, see this trend clinically.
Why do the different suture fusions (types of craniosynostosis) cause different shapes of the head?
Each cranial suture is designed to generate growth in the skull in a very specific area and configuration, ultimately reflecting the size and shape of the underlying brain structure. The overall bone development from cranial sutures occurs in a direction perpendicular to the long axis of the suture. Understanding these two facts, it makes sense that a fusion of each suture independently would cause a unique head shape. The following diagrams and clinical pictures demonstrate the unique forms that occur with each suture fusion:
What are the concerns about a fused suture?
There are a couple of concerns associated with a fused skull suture. First and foremost, the skull is not growing adequately to afford sufficient volume and configuration of the endocranial cavity for the developing brain. Inadequate endocranial volume leads to an increase in pressure within the brain cavity. As the disproportion between endocranial volume and brain volume veers further away from normal, the fluid spaces around and within the brain become compressed, and eventually the brain tissue itself becomes compressed.
Since the brain depends on a large percentage of heart’s output (roughly 30%) to function properly, there is an important hydrostatic gradient between systemic blood pressure and intracranial pressure that is necessary to keep the brain functioning well. There is not an exact answer to the question of “what is normal intracranial pressure” because we have never been able to establish experimentally in what range the best functioning brains in the world exist compared to lower functioning brains. Experimental data suggests that a good estimation of “normal” pressure” is less than 15 mm Hg on average in patients with normal blood pressure. Brains that exist in a range below 15 mmHg seem to be happy and function at their best. We all know from everyday life that a certain activity, like lifting a heavy weight, may be associated with a full feeling in the head. This feeling is caused by obstructed blood flow from the brain back to the heart. The blood backs up in the brain temporarily and leads to transient high pressure. So periods of high pressure are clearly normal for much of what we do as humans. We don’t get too excited by these occasional activity related “high pressure spikes”. However, when a patient experiences a lot of these spikes or their pressure is consistently above 20 mm Hg or so, we start to become concerned.
Another concern of some parents, and less to others, is the shape of the head and its impact on how the child appears when compared to other children. Obviously, the degree of deformity and the value a family attributes to appearance have a great impact here. There are clearly cases of children with very late onset craniosynostosis that have very little change in their external appearance; patients with early, in-utero fusion often have a much more noticeable difference in their external appearance compared to other children. The value of appearance is a very personal consideration. It is important for each patient and family to feel free to express his or her own opinions on this issue. While never the sole concern in the context of craniosynostosis, a family’s opinion on this issue is always valid and important to understand when making decisions on whether or not to treat the disorder, especially surgically.
Do you ever measure pressure to confirm elevated intracranial pressure?
It depends. The only way to accurately measure intracranial pressure is to place a small transcranial wire and monitor the intracranial pressure for several days. This wire is placed in the operating room under anesthesia by drilling a very small hole in the skull, and the patient is then monitored in the hospital settting. Only by measuring the pressure during all phases and activities of life can we really get an accurate measurement and feel for the pressures that any one patient experiences. So while the information is vital, an accurate measurement is a big ordeal. While not that risky, it is very expensive to accomplish and requires several days from work for the family.
We don’t routinely measure intracranial pressure in infants with single suture fusions because we know that they rarely experience high pressure within the first couple of years of life due to their open anterior fontanelle and thin, pliable skulls.
The unique head shape that results from a single suture fusion actually represents the skull’s way of compensating for the rapidly growing brain. The restricted growth at the fused suture means that the other sutures experience more pressure than usual. The sutures, especially those closest to the fused suture, respond to that pressure by generating more bone than they normally would. It is this excessive bone growth at the adjacent sutures that results in the unique head shape and keeps the baby’s intracranial pressure down in the “happier range”. Babies are very sensitive to high pressure and show us fairly quickly when they are experiencing it. We rarely notice an elevation of pressure that would be to the extent of affecting the development of a child with a single suture fusion before 18 months of age. This is not necessarily true when multiple sutures are prematurely fused.
Some experts do worry about the brain’s ability to develop its full capacity in higher cortical functioning (IQ) when it experiences periods of even slightly higher pressure during the first couple years of life. And there is some evidence to suggest that babies who have had craniosynostosis may have very slightly lower IQs when compared to unaffected children. The problem is that this is a very limited data set, full of potential error and miscalculation, and measuring IQs in children is very difficult to do consistently and accurately. Additionally, no one knows what true “normal” intracranial pressure is in infants, and no one has measured it in infants affected by single suture synostosis. If indeed there is a true difference, it is still not known if other genetic or birth related issues could be influencing this difference. So that is a long answer to why we don’t routinely measure intracranial pressure in babies.
There are two sets of patients in which we often do want to measure intracranial pressure. The first group are patients who present to us at an older age (usually >2 years old). They present a unique challenge to us because the bones are much more calcified and difficult to shape into a normal skull at the time of surgery. They also are much less likely to fill in any gaps left behind by surgically expanding the skull. These patients often have experienced a fusion of the skull suture after birth, and therefore have a skull deformity that is much less severe than those who experience fusion in utero. The milder deformity is often the reason that they present later than most other children who fuse in utero. If the deformity is milder, the patient may have adequate intracranial volume that would obviate any need to surgically expand the skull. For this reason, we routinely measure pressure in these children (sometimes several times in early childhood) to determine if we should consider surgery or not.
The second group of patients are those that received an operation for craniosynostosis when they were young children but began to experience signs and symptoms of elevated intracranial pressure several years later. Some of them may have gone on to fuse a second suture after the initial surgery, while others likely did not get adequate expansion at the first operation. While we think our protocols (and our commitment to strictly adhere to them) are very effective at minimizing this group of patients that we treat as babies, sometimes children that were operated on at other centers move to our region and we take up their care. The patients that fit into this category most often are children with single suture craniosynostosis who were treated with a “strip craniectomy” with or without the use of a post-operative helmet or use of an “endoscope”. Others have multiple suture craniosynostosis, which is a completely different set of conditions and almost always requires two or more cranial expansion procedures. We sometimes measure pressure in these patients to confirm a suspicion for elevated pressure when the radiographic signs and the symptoms of the patient are pointing to high pressure. Measurement helps us determine the degree of increased pressure, which is critically important in determining which surgical technique we employ to correct the problem. Because of the firm, calcified skull in older children, our surgical approaches differ greatly when compared to babies. Options include not only traditional osteotomies and bone grafting (ribs and hip donor sites), but also cranial distraction osteogenesis procedures. Which technique we offer depends on the exact details of each case.
What are the Goals of Treatment for Craniosynostosis?
There are three goals of treatment:
- Expand the intracranial volume sufficiently for the brain to avoid high pressure, including the immediate need for more volume and anticipating the future need for brain growth
- Reconstruct the skull into a normal form and appearance
- Provide an intact skull that is protective of the brain for unrestrictive activity
The protocols developed and employed over the last decade by the Craniofacial Team of Texas are focused on consistently delivering on the above goals over the life of the patient. We are dedicated to delivering protocols and techniques that achieve these goals for the patient in a single procedure with minimal to no chance of any revision surgery or second expansions. Although we cannot promise that your child will not need a second surgery, our revision rate at this point in our history for inadequate intracranial volume, cranial defects, or poor form is very low compared to other centers. Clearly, some of the diagnoses present a greater challenge than others.
Our protocols include a strict annual follow up regimen and repeat imaging at 2 years post surgery to ensure that the surgery we performed was not only successful in the short term, but also that the effects are enduring for the patient. Since radiological imaging modalities provide us with several clues about whether the intracranial volume is adequate or not in a non-invasive way, we feel it is imperative to combine imaging modalities with a rigorous clinical follow-up program to evaluate how things are going. The effects of subtle high pressure can be insidious at times, and only close surveillance can pick up any residual high pressure at an early stage before any damage occurs. Long term follow-up and team based surveillance is the only way to properly monitor patients until they reach an age that we no longer have to worry about elevated pressure.
Over the years, we have found that our current protocols are very successful in achieving the above three goals. These results are also enduring over time. We have avoided the urge to jump on the band wagon for the “newest” and “greatest” trend or technique. Some may push an earlier “strip craniectomy”, citing that there is less blood loss. We feel that blood loss is an important operative metric for hospitals, but an operation should never prioritize blood loss over the above three goals. A surgery that focuses on blood loss but fails to achieve all three goals that endure over time will require a second operation with an inherently higher set of risks and a second blood loss event to correct it. This is counterintuitive and not in the long-term best interest of the patient.
What treatment for craniosynostosis is available?
Currently, the only effective treatment for craniosynostosis is surgery.
While the above is consistently true across the world, the design of the surgery, the timing of suture, and the medical devices employed could not vary any more than they do today. When we see such variation in strategy and technique in the treatment of a medical disorder, it usually indicates that there are many approaches that are somewhat effective in achieving most of the goals of the treatment. Which ones are the best is debated ardently among experts around the globe. Many of the strategies do a great job of immediately relieving the threat of high pressure. However, we feel like there are very few that are able to achieve all three goals of permanent pressure relief, a protective skull, and a normal external appearance in a single procedure. We have endeavored over the past decade to develop protocols that do just that and do it consistently.
The Craniofacial Team of Texas, just like other centers, has its opinions about the way things should be done, and we regiment this in a set of treatment and follow-up protocols that are derived from our collective experience and our understanding of the most current data, techniques, and medical devices available. We feel that the treatment of craniosynostosis, like other medical conditions, lacks clearly defined outcomes metrics and lacks discipline around the acquisition of outcomes metrics. While we are currently developing that system of outcomes metrics, we have to continue to rely on “expert opinion” to guide us. This is where the over 45 years of cumulative experience of our medical professionals engaged in a systematic development of protocol driven medicine makes a significant difference in the quality, effectiveness, and consistency of the care that we provide to our patients and the consistent results that we achieve. See Goals of Treatment Section
What are the physical signs and symptoms associated with craniosynostosis?
Often the most obvious sign of craniosynostosis is a unique head shape and orbital asymmetry, although craniosynostosis is not the only cause of a unique head shape. Our team has strong experience in evaluating unique head shapes, determining the cause of each one, and deciphering out other causes from craniosynostosis.
In addition to a unique head shape, the signs and symptoms of elevated intracranial pressure may or may not be present. The most consistent symptom of elevated pressure is the presence of chronic, recurrent headaches. Because there are many different causes of headaches, it is important to distinguish between the patterns of headaches caused by increased intracranial pressure and those that are caused by other reasons. Again, multidisciplinary experience plays an important role in this.
Prolonged elevated pressure and very high pressure cause irreversible damage to the optic nerves (nerves that are key to vision). Sometimes this damage can be found by examination of the retina by a pediatric ophthalmologist (a medical doctor of the eyes). The physical exam finding is called papilledema. Once papilledema is seen on exam, it is an indication that the nerve has suffered a permanent injury that results in worsening vision for the patient.
There is some data to suggest that long-standing or early-onset pressure elevation on the brain can lead to a brain that functions at a lower level than it would have if it never experienced elevated pressure. Longitudinal studies regarding IQ and brain function in children are very difficult to carry out, and comparing these children to unaffected cohorts is riddled with issues that can challenge the validation of these studies. Clinically, children who are experiencing very high pressure from other conditions, like hydrocephalus, do not function very well. Pressure can get so high in some of these cases that it can become life threatening. While most children with craniosynostosis do not experience pressure as high as hydrocephalus, we do see similar pressure effects on some patients with the higher end of the pressure spectrum. The effects of long standing, low-grade pressure are much less clear, for sure.
Lastly, there are a number of radiographic signs that the team looks for on imaging studies. No one sign indicates high pressure, but the presence of several of them together usually supports a presumptive diagnosis of elevated intracranial pressure. A “copper-beaten” pattern to the inner cranial surface, loss of extra-axial fluid spaces, narrowing of the ventricles, effacement of the sulci, and blunting of cerebral gyri all indicate some degree of cephalo-cranial disproportion or, simply, a mismatch between the size of the brain and the volume provided to it by the skull.
How is craniosynostosis diagnosed?
History and physical examination are central to the diagnosis of craniosynostosis. The experience of our team of pediatric neurosurgeons, pediatric craniofacial surgeons, and craniofacial pediatricians allows for the proper evaluation of the unique head shapes caused by single and multiple suture fusions. Although the diagnosis is made clinically, we obtain radiological studies closer to the time of surgery when they are the most relevant to surgical planning.
Radiological Studies for Craniosynostosis
What radiological studies are recommended and when should they be acquired?
Although the diagnosis of craniosynostosis is made by clinical exam, we do recommend a unique set of imaging studies to confirm the diagnosis, evaluate brain morphology, determine the degree of brain compression, and evaluate the venous drainage of the brain. All of these factors affect how we approach and conduct each surgical case. Since the finding of these studies can significantly affect steps we take during the operation, we prefer to obtain these studies closer to the time of surgery.
Two types of studies provide us with all the information that we need:
- Low radiation dose, Craniofacial CT
- Fast-acquisition MRI
We have worked very closely with our neuroradiology colleagues at Austin Radiological Association to design imaging protocols that give us the best information possible with as little adverse effect on the patient. In fact, the Craniofacial Team of Texas led the development of low radiation dose imaging protocols across the country in response to a nationwide concern over radiation exposure from CT imaging. These coordinated studies are obtained quickly and usually without the need for sedation, though sedation capabilities are available when needed.
At what age does the Craniofacial Team of Texas recommend operating on craniosynostosis?
Since a baby born with a single suture fusion is the most common presentation of the disease, we will focus on this group when addressing this very important question. There are a couple of natural biological facts and development/growth issues that affect our protocol when it comes to treating babies with single suture craniosynostosis. As discussed in the section on skull anatomy, a baby’s brain is doubling in size from the time of birth to one year of age. This is seen on the head circumference curve below:
We know that any skull affected by craniosynostosis lacks adequate growth potential for the rapidly growing brain. Additionally, surgery itself affects the growth potential as well. The expansion of the skull, regardless of which surgery technique is used, needs to be enough to accommodate the brain volume of an 18-24 month old child. Since the soft tissue envelope of the skull, the scalp, can only be safely stretched so much during a surgical procedure, it is impossible to expand and maintain the expansion of the skull enough in the first eight months of life to the targeted size of 18-24 months of age. As we discussed earlier, patients with single suture craniosynostosis rarely get into pressure problems before 2 years of age. Our goal is to expand the skull and reform it in a single procedure that minimizes chance of requiring a second procedure to expand the skull and/or patch any defects (holes) in the skull. Taking this into account, one would conclude that surgery should at least be delayed past 8 months of age.
There are additional biological factors at play. Babies have an incredible capacity to generate bone after injury (surgery is a type of injury biologically speaking). They naturally heal fractures very quickly in the first years of life. The skull itself maintains this capacity until about 18 months of age, but is most reliable in all patients up to one year of life. All true expansion procedures involve strategically leaving gaps between cut bones to some degree or another. This is how the expansion actually occurs. So we have two forces here at play: a rapidly growing brain that starts to slow down quite a bit at the 8-9 month age and a skull that heals really well before one year of age.
Lastly, the skull is a very unique shape. This shape is not easily reproduced using firm, calcified pieces of bone that cannot be bent or contoured. It would be similar to trying to make a curved wall out of 2 x 4’s set horizontally…doesn’t work well. Babies’ skulls start to really calcify to a point that they are difficult to bend and contour around 10 months of age. Since bending skulls after 10-12 months of age is impossible, we have to segment it and reconstitute it from a bunch of small pieces instead of using big pieces and bending them. Taking all these factors into consideration, our protocols focus on performing a single procedure at 9 months of age. In reality, anytime between 8-10 months of age gives us very consistent and reliable results. Our goals (see Goals of Treatment) have been consistently achieved by using this time frame and our current protocols.
Some providers suggest that early surgery and pressure relief is better for the brain and may say that 9 months is too late (not validated by large numbers of patients). We do not believe in early surgery designed to be a single expansion procedure since babies do not grow well after a surgical event and the scalp envelope will only allow so much expansion (and not enough for future needs) in the period of 0-8 months when the brain is growing very rapidly. The expansion associated with an early surgery is rarely adequate for a patient long term. An early surgery that does not endure over time necessitates a second procedure with its associated risks. We believe that waiting until 9 months of age allows us to set the patient up for a solution that meets all of our goals of providing adequate intracranial volume, proper cranial form, and a completely protective skull without defects in one surgical procedure. We recognize there may be a role for early, smaller strip type procedures (+/- helmeting) that would be followed later by a definitive expansion procedure in the 8-10 month period. However, we think the data that suggests that early surgery may be associated with better brain outcomes is very preliminary and needs to be repeated and validated before we suggest a child undergo two planned surgical events.
If you would like more information about this craniofacial anomaly, please contact the Craniofacial Team of Texas by calling 512-377-1142 or toll free 877-612-7069 to schedule an appointment or complete an online appointment request.