Craniosynostosis

A newborn's skull is not a single rigid box. It is several bones joined by flexible seams called sutures. Through the first year the brain grows faster than at any later point, the bones drift apart along those seams and make room for it. Craniosynostosis means one of the sutures has fused too early. The brain keeps growing, but the skull can no longer widen in that direction, so all the growth is pushed towards the seams that are still open. That is where the unusual head shape comes from, and it is usually what first raises the question. The condition is uncommon — roughly one baby in two to three thousand — and it frightens families more than it deserves to. Here is where the line runs between an odd shape and a real problem.

What happens to a growing skull

The mechanics are simple, and once you grasp them you can predict the head shape from the suture involved. Bone is added along the edges of a suture, at right angles to it. Once a suture fuses, growth in that direction stops, the remaining seams do double duty, and the head stretches out along the line of the fused seam.

That is why head shape is not a cosmetic detail to a doctor but a pointer to a specific suture. It is also why a single fused suture does not usually squeeze the brain: the volume is made up elsewhere. Space runs short when several sutures close at once, and that brings a separate problem, raised pressure inside the skull, which has its own section below.

What the head looks like, suture by suture

• The sagittal suture, running front to back along the crown, is the commonest finding. The head becomes long and narrow, the forehead bulges and the back of the head is drawn out; from above the outline resembles a boat.
• The metopic suture, running up from between the eyebrows. The forehead takes on a keel shape with a ridge you can feel down the midline, the temples pinch in and the eyes sit closer together; from above the forehead looks triangular.
• One coronal suture. The forehead and eyebrow on that side look pulled back and lifted, the eye socket appears wider and higher, and the tip of the nose points to the opposite side. The asymmetry shows in the face rather than the back of the head.
• Both coronal sutures. A short, broad head with a tall flat forehead, often with an underdeveloped midface. This is the pattern most likely to be part of a genetic syndrome.
• The lambdoid suture at the back is rare. One side of the back of the head flattens, the ear on that side shifts backwards and downwards, and a bony ridge can be felt behind it.

When an odd head shape is not craniosynostosis

The vast majority of misshapen heads that bring parents to a doctor have nothing to do with the sutures. They are positional flattening: the baby spends long stretches on their back with the head always turned the same way, and the still-soft bone gives. Sometimes a shortened neck muscle is behind it, making it uncomfortable to turn the other way.

Looking down at the head from above tells the two apart.

• With positional flattening, the flat area at the back drags the ear and the forehead on the same side forward: from above the head reads as a parallelogram.
• With a fused lambdoid suture the opposite happens: the ear moves back and down, the forehead stays put, and a lump appears behind the ear; the outline is closer to a trapezoid.

Positional flattening is not operated on. It settles by itself if the head position during sleep is varied, if the baby spends supervised waking time on their tummy, if the cot is turned around and the interesting things in the room are moved to the side the baby avoids; a shortened muscle calls for stretches as well. A moulding helmet is used in some cases, and this is where confusion creeps in: a helmet corrects positional flattening or is worn after surgery, but on its own it does not reopen a fused suture.

Signs that should not wait

Head shape is a planned conversation and can wait for an appointment. Signs that the brain is running out of room cannot. Seek care straight away if a baby or child has:

• a head circumference that has stopped increasing or, conversely, jumps and drifts off its usual line on the growth chart;
• a tense, bulging soft spot while calm and not crying;
• vomiting, especially in the early morning and without diarrhoea, along with unusual drowsiness or relentless irritability and weaker feeding;
• prominent, clearly widened veins over the scalp;
• eyes that turn downwards so that a strip of white shows above the iris;
• in an older child, headaches on waking, failing vision, a squint, or the loss of skills already mastered;
• laboured breathing, snoring, or pauses in breathing during sleep.

Breathing deserves a separate word. In some forms the midface is underdeveloped and the nasal passages are narrow, so the child has no choice but to breathe through the mouth. That is not a habit or a minor quirk but a sign of a narrowed airway, and it needs assessing.

What happens at the appointment and what is decided next

The doctor looks at and feels the head — a fused suture often gives a hard ridge under the fingers — measures the circumference and plots it against age, checks the face, the eyes and the symmetry, and asks about the birth, sleeping position and family history. That is usually enough to separate positional flattening from a genuine suspicion.

If the suspicion stands, the child is referred to a craniofacial unit. There the sutures are examined by ultrasound, which works well in infants and involves no radiation, and where necessary by a computed tomography scan with three-dimensional reconstruction, which shows exactly which suture has closed and how the skull has reorganised itself. If more than one suture is involved, or if the face, hands or feet look unusual, genetic testing is offered. Vision and hearing are checked separately.

From there, three paths are possible, and the choice depends on the suture, the age and how the child is doing.

• Watchful follow-up. Mild cases — a slight forehead ridge with no change in skull shape, for instance — are simply monitored.
• Endoscopic surgery. The fused suture is removed through small incisions and the growing brain does the rest of the reshaping, provided the child wears a helmet afterwards. The age window is narrow: it is only feasible in the first months, while the skull is still pliable, so waiting simply removes the option.
• Open reconstruction. The incision runs across the crown, the bones are freed, repositioned and fixed. It is done under general anaesthetic, usually towards the end of the first year, with about a week in hospital. The scar is later hidden by hair.

What to expect further on

For most children, nothing remarkable: the head shape comes right, development follows its normal course and no restrictions remain. Follow-up still continues, closely spaced at first and then yearly or less often, until facial growth is complete.

Things are harder when several sutures are fused or when a genetic syndrome sits behind the condition. One operation is then rarely the end of it: midface surgery may be needed in later years and, alongside it, regular vision and hearing checks, glasses, speech and language therapy, dental and orthodontic treatment, and psychological support. A squint is more common when a single coronal suture is involved, while speech and learning difficulties cluster in the multi-suture forms. Surgery does not always leave a perfectly symmetrical head, and that is worth discussing with the surgeon beforehand rather than afterwards.

One last point, because nearly every family asks. The head shape in craniosynostosis has nothing to do with how the pregnancy went, what the mother ate, or how the baby was carried. The suture fuses for reasons that in most cases remain unknown.

Online consultation

A remote appointment answers the central question well: is what you are seeing a normal variation, positional flattening, or a reason to see a specialist — and how quickly. The doctor will go through photographs of the head taken from above, from behind and in profile, look at how the head circumference has tracked in the records, ask about sleeping position and neck turning, explain what to change about positioning and tummy time, and advise which investigations are worth requesting. It is also a convenient way to work through the plan after a face-to-face visit and to avoid losing time where the child's age narrows the surgical options. The signs listed under urgent care are not assessed remotely: those need an in-person examination without delay.

This material is for information only and does not replace medical advice.