Westermark sign

Westermark sign is a chest x-ray finding of oligaemia (clarified area) distal to a large vessel that is occluded by a pulmonary embolus.

The focal area of increased translucency due to oligaemia is caused by impaired vascularisation of the lung due to primary mechanical obstruction or reflex vasoconstriction.

The Westermark sign has a 14% sensitivity, 92% specificity, 38% PPV, and 76% NPV as reported by Worsley et al. (1993) based on the cohort from PIOPED (Prospective Investigation of Pulmonary Embolism Diagnosis).

History

1938 – Nils Westermark published his chest roentgen findings of 26 cases with autopsy proven pulmonary embolism and a chest x-ray within 2 weeks following death. These patients had areas of anaemia or oligemic peripheral regions of lung parenchyma distal to an occlusive arterial embolus.

In embolism of the pulmonary artery without infarction we get ischaemia of the branches of the pulmonary artery on the peripheral side of the embolus. On the radiogram this ischaemia appears as a clarified area with diminished vascular design corresponding to the extent of the embolised artery. The vascularisation is however maintained in the central parts of the lung. The vascularisation takes however a rapid end to pass over into the above mentioned area of non-vascularisation.

Westermark 1938

Case 2. Examination carried out on day before death from pulmonary embolism. Of note is anaemia of the entire right lung, particularly well marked in its upper lobe and in left upper lobe. The vascular design seems to end abruptly in the central parts of the lung.

Associated Persons

• Nils Westermark (1892 – 1980) [Westermark sign 1938]
• Aubrey Otis Hampton (1900 – 1955) [Hampton hump 1940]
• Felix George Fleischner (1893 – 1969) [Fleischner sign 1959]
• C. H. Joseph Chang (1929 – 2017) [Chang sign 1965]
• Antonio Palla (1950 – ) [Palla sign 1983]

Alternative names

• Relative oligemia

References

• Westermark N. On the roentgen diagnosis of lung embolism: brief review of the incidence, pathology and clinical symptoms of lung embolism. Acta Radiologica 1938; 19(4) :357-372.
• Marshall GB, Farnquist BA, MacGregor JH, Burrowes PW. Signs in thoracic imaging. J Thorac Imaging. 2006 Mar;21(1):76-90.
• Worsley DF, Alavi A, Aronchick JM, Chen JT, Greenspan RH, Ravin CE. Chest radiographic findings in patients with acute pulmonary embolism: observations from the PIOPED Study. Radiology. 1993 Oct;189(1):133-6.
• Maizlin ZV, Cooperberg PL, Clement JJ, Vos PM, Coblentz CL. People Behind Exclusive Eponyms of Radiologic Signs (Part II). Can Assoc Radiol J. 2010 Feb;61(1):44-53.
• Cadogan M. CXR eponyms in pulmonary embolism. LITFL