Flat Head or Craniosynostosis? How to Tell the Difference

You notice your baby's head is flat on one side, or the forehead looks uneven, or the soft spot seems small. You search online and find two very different explanations: positional plagiocephaly, which is common and harmless, and craniosynostosis, which is rare and may need surgery. The anxiety between those two possibilities is what brings most parents to our clinic.

This article explains the difference in plain terms, describes the signs that should prompt a specialist assessment, and sets out what happens if the diagnosis turns out to be craniosynostosis. For a complete guide to the surgical conditions and how each one is treated, see the full craniofacial surgery page.

Positional plagiocephaly: the common one

Positional plagiocephaly is a flat spot on the back or side of the head caused by external pressure, not by a fused suture. It is extremely common. Since the safe-sleep guidelines recommending that babies sleep on their backs were introduced, the incidence of positional head flattening has increased because babies spend more time with the same part of the skull resting on a flat surface.

In positional plagiocephaly the skull bones are normal and the sutures are open. The flattening is caused by the soft, pliable bone of a newborn being moulded by gravity. The important thing to understand is that positional plagiocephaly does not put pressure on the brain, does not affect development and in most cases improves on its own with simple measures.

What positional flattening looks like

When you look at the baby from above, one side of the back of the head is flatter than the other. The ear on the flat side is often pushed forward compared with the other ear. The forehead on the flat side may bulge slightly to compensate. If you run your fingers along the sutures, you will feel no hard ridge. The soft spot (anterior fontanelle) is open and feels soft.

What helps

Supervised tummy time when the baby is awake, alternating the side the baby faces during sleep, and holding the baby upright more often during the day are usually enough. In moderate cases a repositioning programme guided by a physiotherapist can help. In more pronounced cases a cranial moulding helmet may be recommended, but this is for cosmetic improvement and is not medically necessary in the same way that craniosynostosis surgery is.

Craniosynostosis: the rare one

Craniosynostosis occurs in about 1 in 3,000 births. One or more of the joints (sutures) between the bone plates of the skull fuse too early, before the brain has finished growing. Because the skull cannot expand across a fused suture, growth is redirected and the head takes on a characteristic shape that depends on which suture is involved.

Unlike positional plagiocephaly, craniosynostosis is a structural problem. In some cases the restricted skull can cause raised intracranial pressure, which may affect the eyes, development and, rarely, vision. This is why early diagnosis matters: it determines whether the child needs surgery and, if so, when.

Signs that suggest craniosynostosis rather than positional flattening

No article replaces a specialist examination, but there are features that should raise concern and prompt an assessment by a craniofacial surgeon:

• A hard bony ridge you can feel along a suture line, rather than a soft gap
• A soft spot (fontanelle) that is very small, absent or closed unusually early
• A head shape that is getting more unusual over time rather than improving with repositioning
• The abnormal shape was present at birth or appeared very early (positional flattening tends to develop after a few weeks)
• A forehead that is triangular, very flat on one side, or noticeably tall and narrow
• A head that is long and narrow from front to back (like a boat shape when viewed from above)
• Facial asymmetry: one eye appears wider, one eyebrow is higher, or the nose deviates to one side
• Any swelling, bulging of the eyes, or a head circumference growing too fast or too slowly

None of these alone confirms craniosynostosis, and some overlap with positional changes. That is exactly why a specialist assessment, not an online checklist, is the right next step.

How the diagnosis is confirmed

A craniofacial surgeon can often tell the difference with a physical examination: feeling the sutures, assessing the fontanelle, measuring the head and looking at the overall shape from multiple angles. If craniosynostosis is suspected, a CT scan confirms which suture is fused and how the skull has compensated. In straightforward positional cases, no scan is needed.

In India, craniosynostosis is commonly misdiagnosed. Sagittal synostosis, the most common type, gives a long narrow head that is sometimes dismissed as a family trait. Unicoronal synostosis causes a forehead flattening on one side that is sometimes mistaken for positional plagiocephaly. If the head shape is not improving with repositioning or if any of the signs above are present, asking a craniofacial surgeon to take a look is the safest step.

What happens if it is craniosynostosis

If craniosynostosis is confirmed, the treatment depends on the child's age and which suture is involved. There are two broad approaches.

For babies diagnosed very early, usually before three to five months of age, a minimally invasive procedure called endoscopic strip craniectomy may be an option. A small incision releases the fused suture, and a custom helmet then guides the skull into a normal shape as the brain grows over the following months. The advantages are a smaller scar, less blood loss and a shorter hospital stay.

For children diagnosed later, or for more complex multi-suture or syndromic cases, the skull is reshaped using the child's own bone plates in a procedure called cranial vault remodelling. This is usually done between nine and fifteen months of age, and the craniofacial surgeon works alongside a neurosurgeon to protect the brain while rebuilding the skull shape.

Both approaches are covered in detail, along with specific conditions like Apert, Crouzon, Treacher Collins and hemifacial microsomia, on the craniofacial surgery page.

When to seek an assessment

The short answer: whenever you are unsure. A craniofacial surgeon can tell you in one visit whether the head shape is positional or structural, and whether any action is needed. If it is positional, the reassurance is valuable. If it is craniosynostosis, early diagnosis opens up the widest range of treatment options, including the minimally invasive approach that is only possible in the first few months.

Dr Dipesh Rao is a craniofacial surgeon in Bengaluru trained at the Oxford Craniofacial Unit and the Royal Children's Hospital Melbourne. He sees babies with head shape concerns regularly and can give a clear answer quickly. Read more about Dr Dipesh Rao or explore all the conditions we treat.

Frequently Asked Questions

How common is positional plagiocephaly?

Very common. Studies suggest that up to 20 to 30 percent of babies develop some degree of positional head flattening in the first months of life. Most cases are mild and improve on their own with repositioning and tummy time.

How common is craniosynostosis?

Craniosynostosis occurs in about 1 in 3,000 births. It is much rarer than positional flattening, but it is important to identify because it may need surgical treatment.

Can I tell the difference at home?

You can look for certain signs: a hard bony ridge along a suture, an absent or very small soft spot, a head shape present from birth, or a shape that worsens despite repositioning. However, an accurate diagnosis needs a specialist examination and sometimes a CT scan. If you are unsure, an assessment by a craniofacial surgeon is the safest step.

Does my baby need a helmet for positional plagiocephaly?

Most positional flattening improves with repositioning and tummy time alone. A cranial moulding helmet may be recommended for moderate to pronounced cases, typically started between four and six months of age. It is a cosmetic treatment, not medically necessary in the way craniosynostosis surgery is.

What is the ideal age to treat craniosynostosis?

For minimally invasive strip craniectomy with helmet moulding, the ideal age is three to five months, with limited benefit up to seven months. For open cranial vault remodelling, the ideal age is nine to fifteen months, with good results still possible up to twenty-four months. Early referral keeps both options open.

Is craniosynostosis commonly missed in India?

Yes. Sagittal synostosis, the most common type, gives a long narrow head that is sometimes dismissed as a family trait. Unicoronal synostosis causes one-sided forehead flattening that can be mistaken for positional plagiocephaly. If the shape is not improving or if any red-flag signs are present, asking a craniofacial surgeon is the safest step.

Will my child develop normally after craniosynostosis surgery?

For single-suture craniosynostosis treated on time, the great majority of children develop normally. Surgery relieves any restriction on brain growth and restores a normal head shape. More complex syndromic cases may need longer follow-up, and the craniofacial team monitors development as part of the overall care plan.