Overview

Plagiocephaly, commonly known as flat head syndrome, is a condition which can develop in babies at a few months of age. The baby’s head is flattened, usually as a result of prolonged time spent lying down. The effects of this do not usually extend beyond physical appearance and last no longer than several months.¹ However, there is a potential for the abnormal skull structure to either physically damage the underlying brain tissue or restrict its development. 

The brain develops at the highest rate from birth to five years of age, so any neurological complications in these early years can have a significant, lasting impact on the child’s academic and social capacity.² This raises questions about exactly what impact plagiocephaly may have on cognitive development, at what point there is a risk of this happening, and how it can be avoided.

The links made between plagiocephaly and impaired cognitive development are mostly related to a type of plagiocephaly called craniosynostosis.³ Its effects can have lasting effects on vision, hearing, speech, feeding and learning.⁴ 

Links between positional plagiocephaly and cognitive development have been demonstrated but with far subtler effects and mostly only affecting those whose condition is classed as severe.⁵ To reduce the likelihood of these cognitive complications, conservative management options exist for positional plagiocephaly but surgery is usually required for craniosynostosis surgery.¹

The following sections will delve into the processes leading to plagiocephaly and its cognitive complications, and what can be done to reduce the chance of lasting effects in an infant with plagiocephaly.

What is plagiocephaly?

Plagiocephaly is an umbrella term for the flattening of an infant's skull and there are several types known as:¹

• Positional plagiocephaly
• Brachycephaly
• Craniosynostosis
• Scaphocephaly 

Positional plagiocephaly

Positional plagiocephaly is usually the result of an infant lying in one position excessively. This can be due to restricted head movement, either in neonatal units, within the womb or due to neck muscle abnormalities, such as torticollis. 

The term positional plagiocephaly usually refers to its most common form, an asymmetrical flattening of the side of the infant's head. It is differentiated from brachycephaly, affecting the back of the head symmetrically and scaphocephaly, presenting a long, narrow head.⁶ 

Congenital plagiocephaly

Congenital plagiocephaly, also known as craniosynostosis, is caused by a birth defect and risk factors include multiple pregnancies or uterine abnormalities in the mother. Usually, craniosynostosis occurs randomly but it can also be due to an inherited genetic syndrome. Genetic syndromes presenting with craniosynostosis often have other pathological effects too such as hearing loss, facial anomalies, limb defects, and cardiovascular malformations.⁶ 

It is important that a healthcare professional checks for these signs in cases of craniosynostosis. Positional plagiocephaly can be differentiated from craniosynostosis by the misalignment of the ears and bulging of the forehead that also occurs.¹

Craniosynostosis is far rarer than positional plagiocephaly but is more commonly responsible for complications affecting cognitive development.³ In order to understand why this is the case, a basic understanding of the anatomy of the skull in newborns is required. 

The anatomy of plagiocephaly

The anatomy of the skull in newborns reveals why plagiocephaly affects infants specifically. 

A newborn's skull has several specialised features to allow moulding of the head, to fit through the birth canal, and to accommodate for growth of the brain. These features include:⁸ 

• Sutures, which are flexible fibrous joints between bones of the skull that allow the bones to move appropriately as the brain grows 
• Fontanelles, where the bones remain unfused until around 18 months of age 

This malleable nature of the infant’s skull allows for positional plagiocephaly as external forces over prolonged periods of pressure can physically flatten the bone. 

On the other hand, congenital plagiocephaly (craniosynostosis) is caused by the premature closing of sutures. The sutures can close prematurely when the skull fragments grow abnormally or form abnormal dural attachments between the skull fragments and the outer membrane encasing the brain.³ 

This allows for a concrete discernment between positional plagiocephaly and craniosynostosis,as imaging of the head will reveal fused sutures only in the case of craniosynostosis.³ 

The importance of the function of the sutures in an infant's skull explains why there is a stronger link to impaired cognitive development with craniosynostosis, than with positional plagiocephaly. 

How the brain is affected in plagiocephaly

Craniosynostosis has a strong correlation with impaired cognitive development, as the premature closing of sutures means the solid skull restricts brain growth at an earlier stage than normal. As a result, the infant is unable to form additional neurons, and will not have as many as unaffected infants who continue to develop neurons until around 18 months old.⁷ 

Neurons make the connections in the brain which allow us to sense, react, learn, form memories and more. Therefore, affected infants can have visual, hearing, speech, feeding and learning difficulty.⁴ 

If they do continue forming neurons, the increasing brain mass is still restricted to the volume it can occupy by the prematurely solid skull. Though cognitive function may not be directly affected, this causes increased intracranial pressure which results in headaches, vomiting and papilloedema.⁴ 

In positional plagiocephaly, limited evidence suggests a link to impaired cognitive development. Links that have been made show that mild developmental delays are seen in infants and toddlers with positional plagiocephaly when compared to those unaffected, but the severity depends on the degree of their plagiocephaly as an infant. 

Differences in academic achievement have only been noted between unaffected school-age children and those whose plagiocephaly was severe as an infant.⁵ Other studies have also shown decreasing positional plagiocephaly with age, as it was shown to delay the development of gross motor functions up to 6 months of age but have negligible effect beyond this age with infants catching-up to reach normal milestones at 18 months.⁸

How to avoid complications of plagiocephaly

The obvious solution to avoid positional plagiocephaly is to alternate the infant’s position regularly. This is best advice when the infant is supervised and awake but, when an infant is sleeping, medical advice is for babies to be always placed on their back, as per the 1990s ‘Back to Sleep’ campaign.⁸ This position reduces the likelihood of sudden infant death syndrome (SIDS), as it increases the body’s control over the cardiovascular system, and therefore maintains sufficient flow of oxygen to all tissues. SIDS is fatal and so its prevention must be prioritised. 

What other measures can be taken to avoid positional plagiocephaly?

• Encouraging supervised tummy time while the infant is awake, to reduce pressure on the back of the head and promote neck muscle strength
• Alternating the infant's head position during sleep to prevent prolonged pressure on one area of the skull
• Limiting the time infants spend in devices that restrict movement and keep the head in one position
• Using positioning aids such as rolled towels or specialised pillows to support the infant's head during sleep or when lying down
• Physiotherapy for infants with torticollis to improve neck muscle strength and range of motion
• Cranial remoulding helmets may be prescribed to infants with moderate to severe plagiocephaly to help reshape the skull. These apply gentle, constant pressure to specific areas of the skull to encourage more symmetrical growth³ 

How is congenital plagiocephaly managed?

Surgery is usually recommended to reconstruct the craniofacial structure in craniosynostosis. The surgery usually uses stainless steel springs to increase space for the brain to grow and reduce the risk of the sagittal suture closing, which should not occur until adulthood.³

Summary

Plagiocephaly poses concerns for infants, as there are potential implications for cognitive development. The links made between positional plagiocephaly and impaired cognitive development are relatively weak compared to those with craniosynostosis. 

Considering the anatomical changes underpinning each of these conditions through early development, it can be seen that the increased risk with craniosynostosis stems from its characteristic premature closure of sutures in the brain. 

Understanding what is happening in early brain development helps us to formulate advice on how to avoid the effects of plagiocephaly on cognitive function in infants. Skull anatomy underscores vulnerability to external pressures and premature sutural fusion. 

Further research is required to understand the impact of plagiocephaly on cognitive function, especially with regard to positional plagiocephaly. Such research is imperative to the evidence based medicine techniques used to create future advice and guidelines.