When the Cause of Stroke Is Cryptic

By David Kent, David Thaler

Identifying the reason for a stroke can help doctors avert future ones; if the cause remains unknown, mathematics may point toward a probabilistic answer.

This Article From Issue

January-February 2015

Volume 103, Number 1

Page 54

DOI: 10.1511/2015.112.54

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Sudden weakness on one side of the body, slurred or incoherent speech, a droop in the muscles of the face—these are all possible signs of a stroke, an interruption in the circulation of blood throughout the brain.

Normally, oxygen-poor blood from the veins passes from the right atrium and right ventricle of the heart into the lungs to pick up fresh oxygen, then to the left atrium and left ventricle, and finally through the arteries to the rest of the body, including the brain. Following this path, a clot that forms in the veins of the leg would get trapped in the lung, causing a pulmonary embolism; if it was very small, such a clot might be of little clinical consequence. In cases of paradoxical embolism, however, a small opening in the walls of the heart allows the clot to pass directly from the right atrium into the left atrium and then into the systemic arterial circulation, where it can cause a stroke if it disrupts blood flow in the brain.

Illustration by Tom Dunne.

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