Abnormal head shape may be due to congenital or acquired conditions including birth injury, and is the most common reason for referral to a paediatric neurosurgeon.1 2 Birth injuries may present immediately or late, and imaging is rarely required in order to correctly identify the type of injury. However, an understanding of the underlying pathophysiological processes is helpful in order to appreciate potential complications that can occur in association with these injuries. When assessing an infant or child with an abnormally shaped head, it is important to differentiate between birth moulding, positional plagiocephaly and craniosynostosis which may require surgical treatment. The aim of this article is to explain the differences between these conditions, how they are best imaged and demonstrate some of the imaging findings. Definitions are given in box 1.

ANATOMY AND DEVELOPMENT OF THE SKULL IN INFANTS

The skull is formed from multiple separate bones that develop in the first weeks of embryonic life from mesenchyme enveloping the developing brain. The bones progressively ossify later in gestation. At birth the skull bones are separated by connective tissue sutures which allow movement and alteration in the shape of the skull vault during birth. The major sutures include the metopic suture located in the midline between the two frontal bones, the coronal suture between the frontal and parietal bones, the sagittal suture midline between the two parietal bones, and the lambdoid suture between the parietal and occipital bones. The fontanelles are widened, membranous areas at the intersection of sutures. In relation to the major sutures, the anterior fontanelle (AF) is situated between the metopic, sagittal and coronal sutures, with the posterior fontanelle (PF) found at the intersection of the sagittal and lambdoid sutures. Skull growth is primarily driven by growth of the underlying brain which proceeds rapidly to 90% of adult size in the first year of …