Brain ventricles that increase in size could be a sign of cognitive problems and the onset of Alzheimer's disease, say Canadian researchers.

Researchers at the University of Western Ontario used magnetic resonance imaging to examine the brains of 504 people across North America who had enrolled in the Alzheimer's disease neuroimaging initiative — at the onset of the study and six months later.

They found that when ventricles enlarge, the surrounding brain tissue dies. The increase in size occurs during mild cognitive impairment and continues to do so as Alzheimer's sets in and progresses. Ventricles are one of a system of four communicating cavities within the brain and are filled with cerebrospinal fluid.

The study also found that patients who had Alzheimer's at the beginning of the study had 60 per cent more rapid expansion of ventricles compared to people with mild cognitive impairment.

"These findings mean that, in the future, by using magnetic resonance imaging [MRI] to measure changes in brain ventricle size, we may be able to provide earlier and more definitive diagnosis," said Robert Bartha, lead author of the study, in a release.

"In addition, as new treatments for Alzheimer's are developed, the measurement of brain ventricle changes can also be used to quickly determine the effectiveness of the treatment."

Alzheimer's has traditionally been difficult to diagnose, as amyloid plaques, the sticky coverings that form outside neurons, are usually discovered during an autopsy.

The study is published online Friday in the journal Brain.