The most common cause of a misshapen head during infancy is from position-dependent changes in the skull called positional plagiocephaly (deformational plagiocephaly) where the skull bones are abnormally shaped but all of the cranial sutures are open. These infants often have an area on the back of the head that is flatter on one side than the other from positioning of the head in the womb toward the end of pregnancy. As you might imagine, this is as space-related issue and positional plagiocephaly is more common in twins, triplets, etc. Early in life, infants have poor control of the head and are positioned on their back, which tends to cause them to rest on the flatter side more often. Occasionally the preference for lying on one side is caused by torticollis which is an abnormal tightness of the neck muscles that restricts turning the head to one side.
The skull will grow in the path of least resistance. Since the head tends to come to rest on the flat area, the skull can't grow down so it grows away from the area of flatness which tends to worsen it. This pattern or worsening head shape is common if no intervention is taken in the first 4 months of life. Once the infant is able to hold their head up and roll over on their own, this relieves the area of flatness which will start to improve. The major differences between position-dependent changes and craniosynostosis are that the cranial deformity of craniosynostosis continues to worsen with time and carries an increased risk of elevated pressure in the skull, whereas deformational plagiocephaly is self-limited and does not carry an elevated risk for raised pressure in the skull.
In most case of positional plagiocephaly no treatment is required to achieve a normal head shape, because the skull will even out over time. Often times I will recommend placing a rolled blanket or towel under the back on the side of flatness to encourage the baby to rest on the other side of the head. Occasionally, there may be more significant flatness that requires additional help in growing back into a more even head shape. In these circumstances a molding helmet is prescribed. This helmet does not apply pressure to the head. The molding helmet sits up against the areas of prominence and leaves space for the areas that are flat to grow into. Thus, the helmet is shaping growth of the skull in a more directed fashion.
The earlier the helmet is applied, the more effective it will be. The latest that I prescribe a helmet is about 6 months of age, because the skull bones are starting to harden beyond this age which limits the amount of change obtained from a molding helmet. Once prescribed, a scan is created by an orthotist and then the helmet is fitted about a week later. Periodic visits are required with the orthotist to make adjustments to the helmet as the head grows. Occasionally more than one helmet is needed because the child outgrows the first one before treatment is complete. The helmet is usually worn until about 1 year of age.