Dr Glasgow and Mr McGovern comment:

The general thrust of our review of children with less serious head injuries was to advocate an approach based on clinical factors and, in particular, to use these to identify patients in whom immediate imaging was unnecessary. In the latter context, we made reference to the colour of scalp bruising and the fact that a yellow hue would indicate greater age of an injury than would likely be associated with intracranial bleeding—that is, more than six hours or so after injury.

The literature makes clear the difficulties in aging bruises.1-1 1-2 The time taken for bruises to appear depends on several factors—for example, the depth of injury and the volume of blood extravasated. Hobbs and colleagues1-3 state that in superficial bruises, yellowish tinges may appear in three days, although in deeper bruises this may take 7–10 days. One interesting study photographed the evolution of bruises in accident and emergency care patients, in patients, and staff over a very wide age range (largely adults). They concluded that a bruise showing a yellow colour must be older than 18 hours.1-4 The converse was not necessarily true—that a bruise not showing this hue is less than 18 hours old. The authors add, however, that “bruises may not develop a visible yellow colour until much later than 18 hours”. Therefore, the presence of such colouration in a bruise suggests that, other factors being equal, immediate imaging is not essential, which reinforces the prime aim of our review. We are indebted to Dr Light for her informed comment, but are unaware of other relevant literature. It seems to us that this area has more to do with the art than the science of medicine.