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How do we know that infant abusive head trauma has occurred?

Dr Wayne Squier has highlighted some important issues based on the results of two of our papers,1 which concerns retinal haemorrhage2 and subdural effusions3 in infants examined for suspected abusive head trauma. We welcome her feedback and would like to respond to those comments. Squier notes that the two studies are inconsistent with respect to the distribution of sex and premature infants, despite the fact that chronic subdural haematoma was the predominant finding in both studies. We did not report sex and prematurity stratified for chronic subdural haematoma (n = 24) in the retinal haemorrhage study. In this subgroup, there were 15 (62.5%) boys and five (21%) premature babies. In the subdural effusion study, 68% were boys and 34% were prematurely borne. Thus, there was a similar overrepresentation of premature infants and boys in children with chronic subdural haematoma in both studies. The reason for the remaining discrepancy may, as Squier suggests, be selection. The subdural effusion study is based on infants who have been examined by the National Board of Forensic Medicine, while the study on retinal haemorrhage is based on infants who have been diagnosed with abuse at hospital. The abuse diagnosis in the clinical setting may be a working diagnosis that is later on abandoned, and this may occur more frequently in term babies with an even sex distribution, a possibility that we currently are unable to control for. Squier points out that we have not defined admitted abuse in a clear way. This is an essential methodological issue, and we can only regret this shortcoming. Our definition was that the abuse must have been admitted spontaneously in connection with the child being taken to a care institution. We agree that confessions during police interrogations involve a risk of falsepositive cases, which is one of the reasons why we start from spontaneous confessions. Another reason is that confessions during police interrogation only concern cases where the suspicion of assault is based on medical findings. This means that all children studied will have the findings in question. Thus, the connection between the findings will be strengthened by necessity, not tested. Furthermore, falsenegative cases are missed, making it impossible to estimate the sensitivity of the findings for abusive head trauma. So, how can we know that the child has actually been exposed to abusive head trauma? Undoubtedly, observation by an independent witness or filming is the safest way to determine the exposure. In our material, we have identified one filmed case and five cases that were observed by an independent witness. Given that Sweden has only ten million inhabitants, there should be significantly more cases documented in countries with larger populations. We, therefore, urge other researchers to describe such cases without selecting for the presence or absence of findings. This is probably the only way to achieve satisfactory scientific evidence in this important area.