chest radiograph A chest radiograph, called a chest X-ray (CXR), or chest film, is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in med ...

y, the Westermark sign is a

sign A sign is an object, quality, event, or entity whose presence or occurrence indicates the probable presence or occurrence of something else. A natural sign bears a causal relation to its object—for instance, thunder is a sign of storm, or me ...

that represents a focus of

oligemia Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the loss ...

(hypovolemia) (leading to collapse of vessel) seen distal to a

pulmonary embolism Pulmonary embolism (PE) is a blockage of an pulmonary artery, artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include dyspnea, shortness of breath, chest pain p ...

(PE). While the chest x-ray is normal in the majority of PE cases, the Westermark sign is seen in 2% of patients. Essentially, this is a plain X-ray version of a filling defect as seen on computed tomography pulmonary arteriogram. The sign results from a combination of: # the dilation of the

pulmonary arteries A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and t ...

proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

to the embolus and # the collapse of the distal vasculature creating the appearance of a sharp cut off on chest radiography.

Sensitivity and specificity

The Westermark sign, like

Hampton's hump Hampton's hump, also called Hampton hump, is a radiologic sign which consists of a shallow wedge-shaped opacity in the periphery of the lung with its base against the pleural surface. It is named after Aubrey Otis Hampton, who first described it ...

(a wedge shaped, pleural based consolidation associated with pulmonary infarction), has a low sensitivity (11%) and high specificity (92%) for the diagnosis of pulmonary embolism. Put more simply, the Westermark sign is seldom seen in pulmonary embolism. When visible on a chest X-ray, the Positive Predictive Value is only 33%. That is, 33% of the time that Westermark sign is seen on Chest XRay does a pulmonary embolism actually exis

Etymology

It is named after

Nils Westermark Nils Johan Hugo Westermark (September 9, 1892 – January 24, 1980) was a Swedish sailor who competed in the 1912 Summer Olympics. He later became a radiologist, and described the Westermark sign In chest radiography, the Westermark sign is ...

, a Swedish radiologist.

References

Radiologic signs {{med-sign-stub