Craniosynostosis

Craniosynostosis is the premature closure of the open areas between the skull growth plates, often termed sutures, in an infant. When there is no other involvement besides the skull growth plates, the condition is termed Non-Syndromic Craniosynostosis.  There can be some genetic predisposition to craniosynostosis, but most often it occurs spontaneously and is thought to be the result of in-utero growth constraint.  Examples include: small pelvis, low amniotic fluid, as well as, twin births. When a suture closes prematurely, an abnormality of head shape occurs due to compensatory expansion required by the growing brain.  This compensatory growth causes predictable skull deformations that are most often diagnosed clinically, but a CT scan may be obtained to verify the diagnosis.  There are six major skull sutures, two of which, the coronal and lambdoid are paired.

Cranial sutures involved in non-syndromic craniosynostosis include:

  • Metopic Craniosynostosis (Trigonocephaly)
  • Sagittal Craniosynostosis (Scaphocephaly)
  • Coronal Craniosynostosis (Plagiocephaly)
  • Lambdoid Craniosynostosis (Posterior plagiocephaly)

The treatment of craniosynostosis is surgical. In a small percentage of cases surgery is mandated by an increase in intracranial pressure (10-15%) due to changes in head shape, configuration and volume. However most cases are treated because of the resulting aesthetic skull deformities and the team efforts of the craniofacial plastic surgeon and neurosurgeon can optimize the outcome.

Skull Growth

In order to understand craniosynostosis, it is helpful to know about the normal growth of the skull.  The skull is not made up from one single bone, but instead is made up of different bones.  The junctions where these bones meet are called sutures.  We know that sutures are very important in growing children.  The skull gets larger because the brain is growing and putting pressure on the skull to increase in size.  So, if the brain does not grow, the skull does not get larger.  In the first few years of life brain growth is most rapid.  As the brain grows, it stretches the skull bones apart, with the sutures acting like expansion joints. If one of these sutures has fused shut, the skull cannot expand to accommodate the growing brain, so the brain must push the other non-fused sutures further apart so there is enough room for the brain.  This sequence of events leads to the abnormal skull shape.  I often liken this situation to blowing up a balloon with air and then squeezing the filled balloon.  The volume of air is the same, but the shape becomes distorted to accommodate the shape and pressure changes. In altering the shape of the head, essentially the brain and skull are accomodating to the growth plate, or suture, prematurely closing.

Causes of Fusion

The two most common causes for premature closure of a suture are either a change in one of the child’s genes, or from pressure on the skull.  When only a single suture is fused shut, the most common cause is likely to be from outside pressure on the skull.  We know that it is possible to cause craniosynostosis in animals by restricting skull growth while the animal is still in the womb, and it is very likely that this is the primary cause for the majority of the single sutural synostoses in babies.  The uterus is a relatively small space.  We know that sometimes babies can end up in certain positions in the uterus where they cannot move around freely (for example, the breech position).  We suspect that children born with a single sutural synostosis may have arisen from abnormal position in the uterus resulting in pressure on a part of the skull.  If the skull gets caught in a tight place in the uterus, this pressure can restrict the ability of the skull bones to be stretched apart by the growing brain.  Abnormal skull shapes and single suture synostoses are more commonly seen in twins than in single births, further supporting this theory of in-utero constraint.

Usually, when children with a single sutural craniosynostosis mature, they do not pass this trait on to their children.  However, it has been reported (and we have seen cases of this, as well) of a single sutural synostosis being passed from generation to generation.  This hereditary pattern suggests that the single sutural synostosis is caused by a problem with a gene allowing this trait to be passed from one family member to the next.  It is possible to test for some of these genes to see if they are present in children with craniosynostosis . However, it should be remembered that the overwhelming majority of single suture synostoses appear to be the product of two parents with normal genes, and a mother who has normal prenatal care.

Timing of Intervention

When is the best time to do the operation?

Surgery to correct craniosynostosis can be done at any age.  The ideal time is between 4 –10 months, depending on which suture is fused shut.

In favor of the earliest correction are a number of factors:

  • With early operations the skull is less rigid and easier to shape.
  • The younger the infant, the better the chance that any small skull defects that might be left at the end of the operation will fill in.  After one year of age, babies pretty much lose their ability to make skull bone.  So, when operating on an older child, a more extensive operation is necessary in order to fill in all open areas.
  • The longer a child grows with a fused suture, the more other areas of the skull may over-expand because the brain cannot grow near the fused suture; this results  in more drastic changes in the skull shape.

In favor of operating at a later age are a number of factors:

  • The operation may be slightly safer.  The worst possible complication, following both endoscopic and remodeling procedures, is the baby does not survive the operation.  This horrible complication, which is very rare, almost always results from excessive blood loss. As the infant gets bigger, the child can sustain more blood loss, and there may be a decreasing likelihood that a blood transfusion will be necessary. Surgery before 12 weeks of age is unusual unless the deformity is quite severe. I routinely give infants a drug called erythropoietin before surgery (see Procrit Information), which typically raises a child’s blood levels to help prevent the need for blood transfusions, hopefully improving the overall safety of the operation.  I also use a “cell-saver” device that sucks up the blood lost during the operation, filters it, and lets us give the baby back it’s own blood.
  • The other benefit to operating at a later age is that the correction performed is more likely to last a lifetime.

Balancing all of the above factors, it seems that the ideal time to correct craniosynostosis is somewhere between 4 – 10 months, depending on which suture is involved, the severity of the abnormal skull shape, and a number of other factors.

The earliest treatments for single sutural synostoses were performed by neurosurgeons operating alone.  These early procedures, sometimes called “strip craniectomies” or  “Pi procedures,” were similar in that they involve removal of the fused suture, in hopes of releasing the restriction to growth (basically, throwing away a section of the skull).  However, a number of studies proved that these treatments were almost always unsuccessful.  The excised bone usually grows back quickly so that there is no significant change in shape.  However, sometimes the skull will grow back incompletely, leaving a permanent open space of unprotected skull.  The result is that with these older techniques, the skull shape is never normalized, and sometimes children need to have another operation to either correct the skull shape, or to fill in skull defects that never completely healed in.

Remodeling Procedures

Today, children with a single sutural synostosis usually undergo an evaluation by a craniofacial team prior to deciding on surgical treatment.  If needed, surgery is performed by both a craniofacial surgeon and a pediatric neurosurgeon working together (if parents meet a neurosurgeon who recommends operating without a craniofacial surgeon, then I strongly recommend seeking another opinion). Typically, it is the role of the neurosurgeon to safely remove the bone, and the craniofacial surgeon’s job is to rebuild the skull into a normal shape. The specifics of this procedure vary from surgeon to surgeon.

After learning that the “strip procedures”  never completely corrected the abnormal skull shape, craniofacial surgeons recognized that not only is it necessary to remove the bones affected by a fused suture, it is also critical to remodel the surrounding affected skull bones in order to achieve a normal shape.  These remodeling procedures vary, but there are three basic techniques: 1. Surgery is limited to the area of the skull near the fused suture and is done in a single operation.  2. The entire skull is removed, and remodeled in one operation. 3. The skull is treated with two separate operations, one on the back, and then a second one in the front in a staged approach.

In our practice, the surgery to correct a single suture craniosynostosis is always performed with both a craniofacial surgeon and a neurosurgeon. In addition, only a pediatric anesthesiologist with craniofacial surgical experience are typically selected.  During the operation, the family is given hourly updates as to their child’s condition.  The average correction takes around four hours from start to finish. The surgery is performed though an incision that is made from across the very top of the head.

The goal of the operation is to remove the areas of skull that were affected by the fused suture and rebuild the skull into a normal shape (which is slightly over-corrected to compensate for the abnormal growth that that will occur).  In order to rebuild the skull, it is necessary to hold the bones together, so that they can heal.  We use either dissolving stitches or dissolving plates and screws to set the bones.

At the end of the operation, we close the scalp with dissolving stitches.  We never use metal staples or non-dissolving sutures, as these can hurt when they are removed.  Instead, the child is given a shampoo before we leave the room and the hair is combed over the incision. No wraps or dressings are applied.

The child usually will spend one night in the pediatric intensive care unit and are transferred to the floor the following day.  Most of our patients remain in the hospital for about 48-72 hours.  The risks of the surgery are very small at the most experienced centers

Metopic Craniosynostosis (Trigonocephaly)

Metopic Craniosynostosis is one of the more common forms of this disorder, accounting for approximately 40% of all single-suture synostosis. The metopic suture lies along the midline of the forehead and when fused prematurely, leads to a ridge in the middle of the forehead and a triangular shaped appearance to the skull (trigonocephaly). A small fraction of these patients will have increased intracranial pressure and other neurologic abnormalities; which include eye musculature imbalance and mental delays. Correction is usually recommended for improvement in the cosmetic appearance as well as to address any possible underlying neurologic concerns.

Characteristics of metopic craniosynostosis include:

  • Triangular shape of the forehead and orbits
  • Visible ridging along the growth plate
  • Orbital hypotelorism (narrow set eyes)
  • Narrowing or constriction along the temples

Trigonocephaly involves fusion of the metopic suture. The metopic suture runs from the top of the head, at the fontanel or soft spot, down the center of the forehead to the nose. It is different from the other sutures of the skull because it is the only one that normally begins closing in infancy. A ridge can easily be seen running down the center of the forehead and the fontanel is often absent, or closed. In looking straight on at your child, in addition to seeing a ridge running down the center of the forehead, the forehead will look narrow, and the child’s eyes are usually spaced closer together than is normal. When viewed from above the forehead has a triangular shape, like the bow of a boat.

The incidence of trigonocephaly is approximately one in 3,500 births. Some children may be very mildly affected and do not require treatment. There is a term being used currently that may be misleading called mild or moderate trigoncephaly.  This is confusing, as most children fuse this growth plate normally around one year of age. This time frame is variable and therefore a child may close their suture at 8 or 9 months and be considered normal but have some mild features of an early fusion.  A fusion is nearly always an in-utero event and therefore picked up earlier because of the constraints placed on the developing skull.  Trigonocephaly has also been reported to occur when mothers have taken Valproic Acid for seizures.

Those children who fuse somewhere around one year of age can still develop a ridge and have some mild features, but these most often soften with time and rarely ever need a surgical intervention.  But, this diagnosis does have some gray areas that parents find troublesome as their child may exhibit some features.  The decision to operate in these cases, which are seen with some frequency, is whether the aesthetic concerns will be a source of social stigmata in the future. If the narrowing of the eyes, forehead and especially the temple region dictates a sincere concern than operating is the rule.  If the deformities are mild, and therefore much less noticeable, most often an operation is avoided.  This decision process must be entered into with an experienced craniofacial surgeon and parental involvement. Only those children who have overt trigonocephaly require surgical treatment. Children with an isolated ridge running down their foreheads do not require surgery.

Sagittal Craniosynostosis (Scaphocephaly)

Sagittal Craniosynostosis is the most common form of single-suture synostosis (1 per 3000 births). The sagittal suture lies along the midline of the skull. When this suture fuses prematurely, the head cannot grow in width, but must grow in length to accommodate the expanding brain.

Characteristics of sagittal craniosynostosis include:

  • Elongated skull shape (front to back)
  • Narrow skull width (side to side)
  • Midline bony ridge
  • Frontal bossing
  • Occipital bullet or prominence
  • Head circumference often > 90%

When diagnosed early, children with sagittal synostosis are candidates for both minimally invasive endoscopic approach, as well as, open techniques. When children with sagittal synostosis present at older ages, correction involves cranial vault reconstruction, which can be carried out safely using a standard coronal incision from ear to ear that is hidden in the hair. Whether corrected early or late, it is best performed by a skilled pediatric craniofacial plastic surgeon.

Scaphocephaly involves fusion of the sagittal suture. This sutures runs from front to back starting at the fontanel, at the top of the head, and extends backwards along the middle of the skull to the back of the head. Often the fontanel, or soft spot, is absent or closed. A ridge can be seen, or felt, running along the top of the head in between the right and left half of the skull. When viewed from above, the skull is wider near the forehead and gets narrower towards the back of the skull (which is the opposite of what is normal: that is, the back of the skull should be wider than the front). When looking straight on at the child’s face, the forehead seems prominent and the sides of the skull look narrow. Almost all children affected with scaphocephaly require surgical treatment.

Coronal Craniosynostosis (plagiocephaly)

Coronal Craniosynostosis is a premature closure of the skull sutures that lie behind the forehead and run from side to side. Coronal craniosynostosis may be unilateral or bilateral. When both coronal sutures are involved, it is more likely that an underlying syndrome is present. The geneticists will determine if the condition is syndromic or non-syndromic.

Characteristics of unilateral coronal craniosynostosis include:

  • Flattening of the forehead on the affected side
  • Prominence of the forehead on the non-fused side
  • Retrusion and increased height of the orbit on the fused side
  • Ridging along the affected suture

Plagiocephaly involves fusion of one side of the coronal suture. The coronal suture runs across the top of the skull, almost from ear to ear. The soft spot, or fontanel, is located midway between the right and left coronal sutures and is usually absent, or closed, in plagiocephaly. On the side of the skull where the suture has closed, one can typically feel a raised ridge of bone. When viewed from above, the forehead on the affected side is recessed, or further back than the other side (which typically is further forward than normal in order to compensate for the brain’s inability to grow on the affected side). In looking straight on at the child, the eyebrow on the affected side is usually higher and the root, or top of the nose, may be deviated toward the side of the fused suture.

The incidence of plagiocephaly is estimated to be about one in 5000 births. Almost all children affected with plagiocephaly require surgical treatment.

Lambdoid Craniosynostosis (Posterior plagiocephaly)

Lambdoid Craniosynostosis is quite rare and occurs in only 2-4% of patients with craniosynostosis (1 in 300,000). The lambdoid suture is paired and located along the back of the head and it may fuse prematurely on one side or on both sides. Typically, fusion will cause the skull to develop a trapezoid shape, indicating restricted growth at the fused suture and compensatory growth changes surrounding the suture.

It is important to differentiate lambdoid craniosynostosis from positional head deformation in the first months of life as position related head deformities are then easily treated by molding with bands or helmets rather than surgical treatment.

Characteristics of lambdoid craniosynostosis include:

  • Ridging over the fused lambdoid suture
  • Contralateral frontal bossing
  • Posterior displacement of the ear on the affected side
  • Bulging around the mastoid region on the fused side
  • Depressed occiput (back of skull) on the side of the fusion

A diagnosis can usually be made by physical examination, but occasionally a CT scan is necessary to verify true fusion of the lambdoid suture.

Posterior plagiocephaly involves a fusion of the lambdoid suture. This suture is located on the back of the skull. It has a right and left side and is shaped like an upside down “V.” Usually, only one side fuses shut, but rarely both sides will be closed. When viewed from above, the affected side of the back of the head is flatter than the opposite side. One key marker for fusion of the lambdoid suture is a low bump behind the ear on the same side as the fused suture, called a mastoid bulge. Another marker seen when the lambdoid suture is closed is to look and see if the ear on the same side as the posterior skull flatness is pulled backwards. If the ear is forward on the flat side, with respect to the opposite ear, then a skull deformation should be suspected instead of a fused suture. It is critically important to determine whether or not the child truly has a fused suture because skull deformations almost never need to be surgically treated. Making the diagnosis even more difficult is the fact that on plain skull x-rays the lambdoid suture is frequently misdiagnosed as being fused shut. Ideally, the diagnosis of lambdoid synostosis is made by CT scans, read at an experienced center. Children who have lambdoid synostosis and significant flattening of the skull most often require surgical intervention.