MRI increases the incidence of extra-axial intracranial tumour diagnosis


A Norwegian study has found that cerebral, regional magnetic resonance imaging (MRI) can lead to an increase in incidence rates of intracranial tumour diagnosis.

The authors Ole Solheim, department of Neurosurgery, St Olav’s University Hospital, Trondheim, Norway and others say that a subgroup analysis revealed that there was correlation between increased diagnosis of benign extra-axial tumours but not intra-axial tumours. The results were published in Journal of Neurosurgery.

“It is assumed that the observed increase in brain tumour incidence may at least partially be explained by increased use of MRI,” Solheim et al say. They therefore aimed to examine the regional frequencies of cerebral MRI use correlate to regional incidence rates of intracranial tumours and survival of the patients with these tumours.

From data correlated from Norwegian population registries (January 2002 to December 2007), the authors investigated annual regional rates of cerebral MRI scans regional age- and sex-adjusted brain tumours.

The annual number of cerebral MRI scans increased substantially, according to the results, during the study period, with large regional differences. The authors also report a “steady annual increase in diagnosed intracranial tumours.”

They ascertained, from 50,000 annual scans and 6,363 primary tumours found during the study period, that were was a “positive correlation between the annual number of cerebral scans per 100,000 capita and age- and sex-adjusted incidence rates of intracranial tumours varies in Norwegian counties” (Spearman’s rank correlation coefficient=0.35, p<0.001).

An increase in one MRI per 100,000 capita per year results in a 0.004 (95%; confidence interval 0.002–0.006) increase in diagnosed intracranial tumours per 100,000 capita per year (p<0.001), according to the study.

A subgroup analysis also demonstrated that there was a correlation between MRI and the increased incidence rate of extra-axial tumours (p=0.04, Spearman’s rank correlation coefficient =0.28), but not intra-axial (p=0.394). The association between MRI scans per capita and overall survival was associated with the number of cerebral MRI scans per capita in the county of residence at the time of diagnosis (log-rank test p=0.029). However, after adjusting for year of diagnosis and geographical health region of the Norwegian neurological centres, this was found not to be statistically significant (p=0.076).

Concluding, Solheim and colleagues say: “Largely due to the incidental discovery of benign extra-axial tumours, regional differences in the use of cerebral MRI in outpatients affect observed incidence rates of intracranial tumours.”