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).

westermark sign oligemia pulmonary embolus
Westermark sign: relative oligemia in right sided pulmonary embolus. Hampton hump is also visible


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

Alternative names
  • Relative oligemia



the names behind the name

Doctor in Australia. Keen interest in internal medicine, medical education, and medical history.

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