Overrepresentation of males in traumatic brain injury of infancy and in infants with macrocephaly: further evidence that questions the existence of shaken baby syndrome.

Shaken baby syndrome (SBS) has been thought to be caused by violent shaking of an infant and is characterized by the triad of findings: subdural hematoma (SDH), retinal hemorrhages, and neurologic abnormalities. The triad is not specific for SBS and can be seen in accidental trauma and in certain medical conditions. Recent observations, however, question whether SBS exists. Herein, we review the gender differences in 3 groups of infants with traumatic brain injury: (1) neonates with SDH from birth trauma, (2) infants with SDH from accidental trauma, and (3) infants with SDH from SBS. Gender differences are also presented in a fourth group of infants with macrocephaly related to increased extra-axial fluid spaces (IEAFS). Compared with the expected male frequency of 51.4% in newborns, there was a statistically significant overrepresentation of males in each of the 4 groups-65.3%, 62.2%, 62.6%, and 68.8%, respectively. We believe that the most likely explanation for these findings relates to the larger head size of the male compared with the female which has several relevant consequences. First, the larger head circumference of a male newborn compared with a female newborn may increase the likelihood that a male newborn will incur a small SDH from the minor trauma of the birthing process that can later rebleed and present with a symptomatic SDH that could be misdiagnosed as SBS and child abuse. Second, a short fall would have a greater likelihood of causing a SDH in a male infant than a female infant who could subsequently become symptomatic from hours to weeks later and could thus present as an unexplained SDH. Third, infants with macrocephaly related to IEAFS may be at increased risk for developing a SDH from the larger head size and greater tautness of the bridging vessels in the extra-axial fluid spaces. We believe that many infants who have been diagnosed with SBS have been given incorrect diagnoses of child abuse. Rather, their SDH may occur as a result of a small SDH from the birthing process that enlarges during early infancy, a short fall, or from macrocephaly with IEAFS.