This is an older answer that I had posted:

Traumatic Brain Injury and Brain Tumors

Wise Young, Ph.D., M.D.
W. M. Keck Center for Collaborative Neuroscience
Rutgers University, Piscataway New Jersey, 08854

Quote Originally Posted by Sebastiang

"At the time of my injury I also suffered a head injury that left me in a coma for a week. The head injury left probably a one inch by one inch indention in my head that is probably a 1/16 or less, not sure. My question is whether an injury to the head such as mine increases the chances of a brain tumor? I think that I have read something regarding that and was just curious. My wife had our first baby last month and I was thinking today how important it is now to stay healthy and alive for my wife and boy."
I understand your concern. I don't believe that brain injury causes tumors in a vast majority of people. There have been occasional reports of people who have developed brain tumors at the site of the brain injury. However, it is not clear whether these people already had a disposition to have brain tumors and the injury simply aggravated that predisposition. Published population-based studies suggest that people with brain injuries do not have a higher risk of having brain injury than people who have not had such injuries.

To prove that brain injury caused the tumor, we need definitive evidence that brain tumor was not present before the injury. That evidence is seldom available. Brain injury is so prevalent, i.e. so many people have had a history of a bump on the head sufficient to cause a period of unconsciousness, that one would expect that a significant fraction of people who develop brain tumors to have had a history of brain injury. We also don’t have complete followup data on large populations of people who have had brain injury.

I summarize below several recent studies on the subject. Salvati, et al. (2004) reported four cases of “post-traumatic glioma” and reviewed the literature on the subject. All four cases involved brain gliomas developing from the site of an old brain injury and were not observed at the time of injury. Thus, this suggests that it can happen but the data does not give a clear idea of how prevalent it is. Magnavita, et al. (2003) reported a case of a man who suffered severe injury and then developed a glioma at the site of the injury. However, Nygren, et al. (2001) published the largest population-based cohort study on the subject. They established complete followup of 311,006 Swedish patients and found 281 cases of brain tumors. Detailed analyses showed no significant association of brain tumors with traumatic head injury.

In summary, the risk of brain tumors after brain injury is too small to be detected on large-scale population analyses. On the other hand, there have been several cases of people who have developed brain tumors at their injury site. Given this situation, it is probably prudent to get regular MRI scans of your brain every two years. Other than that, I would not worry about it. It is entirely possible that the people who did develop a brain tumor at the site of their injury would have developed tumors anyway but the injury may have aggravated that tendency.


References Cited
  1. Salvati, M, Caroli, E, Rocchi, G, Frati, A, Brogna, C and Orlando, ER (2004). Post-traumatic glioma. Report of four cases and review of the literature. Tumori. 90: 416-9. Department of Neurosurgery, INM Neuromed IRCCS, Pozzilli, Italy. AIMS AND BACKGROUND: To add a further contribution to the literature supporting the relationship between previous head trauma and development of glioma. METHODS: We report on four patients who developed brain gliomas in the scar of an old brain injury. RESULTS: All cases fulfilled the widely established criteria for brain tumors of traumatic origin. In all of our cases there was radiological evidence of absence of tumor at the time of the injury. CONCLUSIONS: We believe that in specific cases it is reasonable to acknowledge an etiological association between a severe head trauma and the development of a glioma. This assumption is further sustained if there is radiological and surgical documentation of the absence of neoplasia at the moment of the trauma.
  2. Magnavita, N, Placentino, RA, Mei, D, Ferraro, D and Di Trapani, G (2003). Occupational head injury and subsequent glioma. Neurol Sci. 24: 31-3. Institute of Occupational Medicine, Catholic University School of Medicine, Rome, Italy. We report the case of a policeman who suffered a severe head injury to the right temporoparietal lobe while driving a police car. Four years later, the patient developed a neoplasm at the precise site of the meningocerebral scar. Histological examination confirmed a glioblastoma multiforme adjacent to the dural scar. Radiological documentation of the absence of tumor at the time of injury, exact localization of the neoplasm in the injured cerebral area, and latency of the cancer supported the hypothesis of a causal relationship with brain trauma. Physicians faced with brain neoplasms in adults should carefully investigate the patient's personal history of head trauma. When a relationship with occupational head injury is probable, reporting of suspect occupational illness is compelling.
  3. Nygren, C, Adami, J, Ye, W, Bellocco, R, af Geijerstam, JL, Borg, J and Nyren, O (2001). Primary brain tumors following traumatic brain injury--a population-based cohort study in Sweden. Cancer Causes Control. 12: 733-7. Department of Rehabilitation Medicine, Karolinska Institute, Danderyd Hospital, Stockholm, Sweden. OBJECTIVES: The aim of this study was to explore the association between traumatic brain injury and brain tumor development. METHODS: A cohort of patients hospitalized for traumatic brain injury during 1965-1994 was compiled using the Swedish Inpatient Register. Complete follow-up through 1995 was attained through record linkage with the Swedish Cancer Register, the Cause of Death Register, and the Emigration Register. Standardized incidence ratios (SIRs), defined as the ratios of the observed to the expected numbers of brain tumors, were used as the measure of relative risk. The expected number of brain tumors was calculated by multiplying the observed person-time by age-, gender- and calendar year-specific incidence-rates derived from the general Swedish population. RESULTS: The cohort included 311,006 patients contributing 3,225,317 person-years. A total of 281 cases of brain tumors were diagnosed during follow-up. No associations were found between traumatic brain injury and the risk of primary brain tumors, neither overall (SIR: 1.0; 95% confidence interval (CI): 0.9-1.2), nor in analyses broken down by main groups of brain tumors. Stratified analyses according to age at entry into the cohort, year of follow-up, and severity of the brain injury all showed essentially the same null results. CONCLUSION: No association between traumatic head injury and primary brain tumors has been found.