In research that is likely to have a significant effect on how children with minor head injuries are treated, Swedish scientists have shown that even low doses of radiation can impair intellectual development.

The doses involved are typical of those used in CT scans, which may sometimes be done to check if there is any damage after a bump on the head. The authors of the research say that CT scanning after minor head trauma now needs to be reconsidered.

A team from the Karolinska Institute in Stockholm, with colleagues in Harvard and Athens, followed up more than 3,000 men who had been given radiation treatment for haemangioma, an excessive growth of blood vessels in the skin, which includes “strawberry marks”.

Such marks often occur in babies, and 80 per cent are on the head and neck. They normally disappear within a few years but sometimes require treatment by laser or surgery.

But in the past, low-intensity radiation was used in the form of X-rays. The team, led by Dr Per Hall, examined the educational level achieved by 3,094 men treated in this way between 1930 and 1959.

They report in the British Medical Journal that the more radiation the boys were given before the age of 18 months, the lower their subsequent intellectual level. Those given the highest doses were about half as likely to attend high school and scored less well on intelligence tests given when they were called up for national service at 18.

Treatment to the front of the skull tended to have greater effects than to the back because more critical parts of the brain are towards the front.

The team points out that the radiation levels experienced during CT scans are similar to those found to have caused the damage. So although other therapies have replaced radiation for treating strawberry marks, there may still be a risk for those scanned by X-ray computerised tomography to assess if there is any brain damage after a bump on the head.

Scanning is not normally recommended but clinical practice “dictated by legal and financial considerations does not always adhere to these protocols”, the team writes.

“The risk and benefit of computed tomography scans in minor head trauma need re-evaluating.”

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