Introduction

Children are not simply small adults. They show a different spectrum of disease from adults, and congenital anatomical variants play a far more important role in disease pathogenesis. An appreciation of normal paediatric anatomy is crucial to the recognition of these variants. The main differences in radiological anatomy between adults and children are due to the following.

Differences in size

The average baby weighs between 3 and 4 kg at birth. Adults may weigh over 100 kg.

Differences in the proportion of many organs

The weight of the neonatal suprarenal gland, for example, may be 30% that of a normal kidney. A normal suprarenal gland may therefore be mistaken for a kidney, if the kidney is absent.

The imaging technique and projection used

Expediency demands that the most rapid and straightforward imaging techniques are used in young children. The projections may not be those used routinely in adult radiology and magnification, obliquity and movement artefact are more commonly encountered than in adult practice. The anteroposterior projection is used routinely for chest radiography in young children, which may result in significant cardiac magnification.

Ultrasonography is widely used in paediatrics, where its real-time and cine-loop playback facilities are of particular value when imaging a moving target. However, the appearances of organs, when scanning at high frequencies, do not always correspond directly with those seen at lower frequencies, and the presence of more acutely curved reflecting surfaces in young children (such as the diaphragm and posterior bladder wall), increases the incidence of mirror image artefacts, which can give the false impression of the presence of a mass.