Schizophrenia is the most common form of psychotic mental disorder, with a point prevalence generally estimated to lie between 0.6–1.0%. Genetically informative studies have indicated a multifactorial aetiology, with an important heritable (genetic) component, but with environmental exposures also undoubtedly relevant. The “neurodevelopmental hypothesis” has informed a body of research that fairly consistently identifies birth complications as a risk factor for the later onset of schizophrenia.^1,2

Injury to the head or brain after birth and beyond has been posited as a risk factor for psychosis for many decades but has enjoyed little systematic research (see Lishman,³ van Reekum et al,⁴ and Fujii and Ahmed⁵ for reviews). The purpose of this article is to review this information systematically. Computerised databases including Medline and PsychInfo were searched using head/brain injury and psychosis or schizophrenia as search terms, covering the period from 1966 to end 2003. Citations from published reviews were also retrieved and yielded important articles and monographs, some published more than two decades ago, not included in these databases.

Four types of study design have been used to assess the relation between head injury and schizophrenia: the case report; the long term follow up of series of head injured persons; the cross sectional survey; and the case–control study.

CASE REPORTS

Case reports document individual unusual clinical events or episodes. The report from O’Callahan and colleagues⁶ is a good recent case in point. The striking circumstance here was the onset of schizophrenia in a previously well 16 year old, with no other risk factors, two years after a significant head injury involving a blow to the left frontotemporal region. His parents commented that “he was never the same since the accident”. However, it is possible that the onset of schizophrenia was incidental to the head injury, and …