Stroke site is often not right.

Thousands of strokes in the right half of the brain may go unrecognized because their symptoms are less distinctive than those of left-side strokes, a statistical analysis suggests. In most people, left-side strokes can affect coordination in the dominant hand and can damage the brain's language centers, impairing speech. Similar interruptions in blood flow to the right brain, on the other hand, tend to cause absented-minded behavior that might be mistaken as a normal part of aging.

Christian Foerch of Johann Wolfgang Goethe University in Frankfurt and his collaborators reviewed data on some 20,000 stroke patients, age 70 years on average, who had been hospitalized in Germany between 1997 and 2002.

A majority of the diagnosed strokes--11,328 versus 8,769--had occurred in the left sides of the patients' brains. Compared with severe strokes, mild strokes were particularly biased toward the left hemisphere, the researchers report in the July 30 Lancet. The researchers say that they see no reason why strokes shouldn't be evenly distributed across the brain.

The patterns in the data led Foerch and his colleagues to suggest that many right-side strokes, particularly mild ones, escape diagnosis because the resulting deficits aren't apparent enough to be perceived as signs of an attack.--B.H.