Positional or deformational plagiocephaly (play-GEE-oh-sef-alee) is the most common cause of an abnormal head shape. This is most often caused by the position of the baby’s head both in the womb, as well as shortly after birth. These babies are most often born with a flat area on one side of the back of their head.
All newborn babies have poor control of their head. If they have a flat area on the back of their skull, they will come to rest on the flatter area when they are laid on their back to sleep. Lying on the flatter side can cause it to continue to become flatter, because the skull will grow away from the flat spot that is supporting the weight of the head. This worsening of the head shape is expected to continue for the first four months of life, until these babies are able to lift and control their heads better. A molding helmet may be used to help correct the head shape if the head shape is:
- Very abnormal
- Not improving rapidly by age 6 months
A helmet works by harnessing the rapid growth of the skull. It guides the skull growth in the direction of the abnormal flatness for a rounder shape.
The figures above demonstrate two key differences between craniosynostosis and positional plagiocephaly.
Top down view – In positional plagiocephaly all of the cranial sutures are open, and there is only a shifting of the skull forward on the flattened side – looks like a parallelogram which has equal length sides. Plagiocephaly from craniosynostosis results from a growth restriction so one side of the skull is shorter than usual and the opposite side is longerthan usual which looks like a trapezoid.
Back view – Despite the significant flattening of the skull on the right side, the base of the skull is generally level in positional plagiocephaly. In lambdoid craniosynostosis there is a significant bulging down of the mastoid (bone behing the ear) and a tilt of the base of the skull. This bulge is absent in positional plagiocephaly. The tilt of the case of skull can be seen at the skin level in a tilting of the hairline at the base of the neck.
The differences between positional plagiocephaly and craniosynostosis:
- Craniosynostosis continues to get worse throughout infancy because the suture is permanently closed.
- Position-dependent changes will typically worsen until age 4 months and then get better over time as the babies improve their head control and are able to roll over because the sutures are open and will continue to grow equally.
- Craniosynostosis increases the risk of abnormally high pressure on the brain.
- Position-dependent changes do not affect the health of the brain.