The cause of a type of stroke that affects about 35,000 people across the UK each year has been uncovered by researchers and may explain why some medications are ineffective as treatment.

Lacunar strokes, which account for a quarter of all strokes in the UK, had been linked to the blockage of arteries in the brain by fatty deposits.

However, a study published on Wednesday suggests they are not caused by blocked arteries but by the enlargement and widening of arteries in the brain.

This would help to explain why aspirin and other blood thinners, commonly used to prevent ischaemic strokes, are not as effective in preventing lacunar stroke.

The research by academics at the University of Edinburgh and the UK Dementia Research Institute analysed 229 patients who had experienced either a lacunar or mild non-lacunar stroke.

Maeva May, the director of policy for the Stroke Association, said the findings “illustrate the value of research and the potential it has to change the lives of stroke patients”.

“There is still so much we don’t know about stroke despite it being the leading cause of complex adult disability and the fourth leading cause of death in the UK,” May said.

“Answering these questions and developing effective treatments is crucial to help ensure a good recovery for the 240 people who survive stroke every day in the UK.

“Stroke research is chronically underfunded, with less than 1% of total UK research funding spent on the condition. This study – and more of its kind – need to be a national priority across the NHS, government and the wider research community with clear pathways to carry breakthrough discoveries from laboratory to patients.”

More specifically, the study found that the narrowing of large arteries was instead more commonly seen in other types of stroke. Instead, widening arteries showed strong links to lacunar disease, with patients who experienced this being more than four times more likely to have a lacunar stroke.

Joanna Wardlaw, a professor of applied neuroimaging at the University of Edinburgh and group leader at the UK Dementia Research Institute, said: “This study provides strong evidence that lacunar stroke is not caused by fatty blockage of larger arteries, but by disease of the small vessels within the brain itself.

“Recognising this distinction is crucial, because it explains why conventional treatments like anti-platelet drugs are not as effective for this type of stroke and highlights the urgent need to develop new therapies that target the underlying microvascular damage.”