This loss of tissue, which comprises brain's grey matter, leads to decreased neurocognitive functions -- perception, memory, awareness, capacity for judgement -- and may hasten the onset of dementia.

Approximately 11 months after patients underwent bypass, aimed at restoring blood flow to the brain, researchers observed a 5.1 percent increase in brain tissue thickness on MRI scans, reports the journal Stroke.

"We were pretty astounded when we saw the results because they were quite unexpected," said Michael Tymianski, neurosurgeon at the Krembil Neuroscience Centre, specializing in neurovascular diseases, according to a University Health Network statement.

"Our goal with the surgery was to halt further loss of brain tissue due to strokes, so it was remarkable to see the loss was actually reversed," added Tymianski.

This is the first surgical treatment which has been shown to restore lost brain tissue. The average age of the patients in the study was 41 years.

"The re-growth of brain tissue has only been observed in an extremely limited number of circumstances," said Tymianski.

"We consider this so important because one of the most important health issues facing our population is chronic cerebrovascular (stroke related) disease, which leads to neurocognitive impairment and reduces quality of life."