Occipital plagiocephaly: an epidemic of craniosynostosis?

Craniosynostosis needs to be distinguished from more common postural asymmetry

“A bizarre epidemic … 400% increase since 1992.” “Unkind cut: some physicians do unnecessary surgery on heads of infants.”1 These terms were used last year by the Wall Street Journal, in company with the British media, to report that the incidence of posterior skull asymmetry, or occipital plagiocephaly, and its surgical management, had increased to epidemic proportions. Such headlines have resulted in anxiety among parents, general practitioners, and paediatricians, and it is therefore important to be clear about the causes of the asymmetry.

One cause of plagiocephaly is craniosynostosis, which is premature fusion of the cranial sutures—the adaptive fibrous joints between the bones of the skull. The resulting abnormal skull shape is usually an isolated anomaly but it may be associated with a craniofacial syndrome such as that of Crouzon or Apert. The skull shape is predictable from the suture or sutures involved. Premature fusion of the lambdoid sutures, which separate the occipital from the parietal bones bilaterally, may cause occipital plagiocephaly.

Premature lambdoidal fusion is nevertheless rare.2 3 The apparently increasing incidence of babies presenting with occipital flattening, either unilaterally or bilaterally, has coincided with current advice to nurse infants in a supine position to combat cot death.4 This phenomenon represents postural, or deformational, plagiocephaly, resulting from unrelieved pressure on the occiput. Asymmetrical influences on the skull base caused by torticollis or cervical spine anomaly may have a similar effect.

In reviewing 75 children presenting consecutively with occipital plagiocephaly to the supraregional craniofacial centre at Great Ormond Street Hospital for Children we have identified some characteristic features of the course of this “epidemic.” Two thirds of the infants and children were boys; two thirds presented with a right sided unilateral flattening; and in two thirds this asymmetry had started some time after birth, progressed until around the age of 6 months, and remained stable thereafter. Half the group showed asymmetry of head turning. The delayed presentation and consistent history of asymmetrical head turning is not characteristic of lambdoid synostosis, in which the head shape is abnormal from birth. Postural plagiocephaly, related to the deformational asymmetry of head turning, is a far more likely cause.

Postural plagiocephaly and true lambdoidal synostosis can be distinguished by clinical examination and confirmed by routine radiological investigation.2 Lambdoid synostosis produces a unilateral occipitoparietal flattening when viewed from behind. The territory of the lambdoid suture presents as a palpable bony ridge, with a bony prominence at the skull base behind the ear on that side, which is displaced inferiorly and posteriorly. The skull base thus seems to tilt to the affected side, giving the head a parallogram shape when viewed from behind. Although the postural group also displays unilateral occipitoparietal flattening, there is no palpable bony ridge of sutural fusion and no bony prominence at the skull base behind the ears, which are level. The ear on the flat side is displaced anteriorly rather than posteriorly and often folded forward. The skull base has no tilt, and therefore the head does not appear as a parallelogram from behind. True lambdoid synostosis is readily distinguishable radiologically, appearing sclerotic on plain radiography and obliterated by bone on computed tomography. The suture remains radiologically open in the postural group.

Why is it important to distinguish the synostotic from the deformational? Clearly the course of the two conditions is different, and this directly affects clinical management. True synostosis is likely to have been present from birth, is progressive, and is unlikely to improve spontaneously. It confers the risk that intracranial pressure may be raised, although this occurs in less than 10% of cases when only a single suture is implicated.5 Postural plagiocephaly, however, confers no risk of intracranial pressure disturbance, and in over 70% of our series the skull shape improved spontaneously. As the child matures and head control improves, the plasticity of the skull base initially allows the deformity to stabilise and then gradually improve. As scalp hair grows the cosmetic deformity becomes less noticeable. The spontaneous improvement may be encouraged by regular changes in sleeping position, perhaps helped by orthotics.6 In severe cases surgical correction may be proposed, but parents should be aware that this would be a cosmetic procedure and not without risk in view of the proximity of the posterior dural venous sinuses.

Thus in most children presenting with an occipital plagiocephaly there will be no craniosynostosis, and even when there is, functional impairment is unlikely. Distinguishing between craniosynostotic and positional plagiocephaly is, however, very important, as surgical intervention for cosmesis is only rarely indicated.