The issue of the relationship between psychosis and injury has always been difficult for psychiatrists to resolve. In general, my own view is that if there is a very close temporal relationship between the injury and the psychosis there could well be a relationship. Complications include premorbid symptoms, cannabis use after the injury and a previous history of psychosis. The matter is a little clearer with regard to traumatic brain injury.
The research literature in relation to psychosis following traumatic brain injury reveals that there is a causal link between the two. Some of the significant findings are:
Batty, R., et al. (2013). Psychosis Following Traumatic Brain Injury. Brain Impairment. 14, 21-41
Fujii, D and Fujii, D. (2012). Psychotic Disorder due to Traumatic Brain Injury: Analysis of Case Studies in the Literature. The Journal of Neuropsychiatry and Clinical Neurosciences.24, 278-289.
Is Traumatic Brain Injury A Risk Factor for Schizophrenia? A Meta-Analysis of Case-Controlled Population-Based Studies: Schizophr Bull. 2011 Nov; 37(6): 1104–1110.