RESPONSE

To the Editor: Miller and Miller 1 reanalyze data from others to suggest that male sex increases the risk of subdural hemorrhage after birth or head injury in infants and children. As pediatric intensivists involved daily in the care of severely head-injured children, we are aware of fundamental errors in the analysis and interpretation that undermine this finding. Their putative evidence is a recorded excess of males with subdural bleeding from a variety of causes. Any comment about a male preponderance in subdural bleeding has to consider a male preponderance in the incidence of injury. Only if subdural bleeding occurs in a higher proportion of male children after severe head injury (rather than simply numerically more children) can their hypothesis be sustained. It is regrettable that despite 117 references, neither Miller and Miller nor the reviewers thought it appropriate to consider the unambiguous data that there is a very significant male preponderance in severe head injury at all ages. The seminal article of Tilford et al, analyzing 98,023 critically head-injured children, describes 69,150 males (70.5%). Similar proportions are evident in the French data set (67% of 585 cases) and the UK Paediatric Intensive Care Audit data (69% of 620 cases). These data combined give us 69,957/99,223 = 70.5% male preponderance. This difference remains in the youngest age groups. Miller and Miller provide tables describing the absolute number of cases by sex of subdural bleeding after accidental (Table 2; 62.2%, males 163/262) and inflicted trauma (Table 3; 62.6% males, 1007/1609). If we assume that their figures are correctly extracted from the literature then it is a simple matter of estimation of the difference between proportions in comparison to the data previously mentioned. We observe an absolute risk reduction for subdural bleeding with male sex of around 7% in both scenarios (95% confidence interval, 2%Y13% for accidental [P = 0.003] and 5%Y9% for inflicted injury [P G 0.0002]; significance of difference between 2 independent proportions). Put simply, there is no evidence that a higher proportion of male children develop subdural hemorrhages than would be expected from the baseline trauma epidemiology. Miller and Miller’s hypothesis therefore can be refuted. The situation should not be confused by considering birth-related subdural bleeding where head size may indeed contribute to a differential level of trauma during childbirth (including subdural bleeding) in male neonates. Unfortunately, the article is further weakened by misquotations of the literature in describing subdural hemorrhage frequency. For example, of the 4 largest series quoted in Table 3, figures extracted from 3 of these series are incorrect. The figures presented from Wells et al are those for all types of intracranial hemorrhage (including 80 cases with epidural hemorrhage, 36 with subarachnoid, and 13 with intraventricular bleeding) rather than subdural bleeding as described. The Canadian data are similarly misquoted in that 364 cases are presented by Miller and Miller, whereas the number with subdural bleeding is presented as 313 in the Canadian article. The article of Jenny et al suffers the same fate as that of Miller and Miller, incorrectly analyzing 173 cases (the number of head injuries) not of cases with subdural hematomas (n = 150). Perhaps the most extraordinary element of this article is the interpretation applied to these flawed data. The authors suggest (Fig. 1) that slowly enlarging subdural hemorrhages in at-risk cases underlie what is misdiagnosed as shaken baby syndrome. This is inconsistent with the typical history of acute collapse, the imaging of thin-film subdural hemorrhages (not space-occupying hematoma), and the pathology of the triad of predominantly diffuse hypoxic-ischemic encephalopathy. The authors themselves restate these features. Articles such as this that lack precision in data collection and analysis and then build dramatic interpretations on these flawed analyses do not advance knowledge. Worse, they may contribute to misdiagnosis of inflicted head injury, thereby exposing vulnerable children to risk.