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The theory behind the sign is either obstruction of the pulmonary artery or distal vasoconstriction in hypoxic lung 3.
In one study (PIOPED) this sign was present on ~10% of chest x-rays of patients with confirmed pulmonary embolus 2.
- focal peripheral hyperlucency secondary to oligemia resulting in a collapsed appearance of vessels distal to the occlusion 2-4
- central pulmonary vessels may also be dilated 3
History and etymology
The Swedish radiologist Nils Johan Hugo Westermark (1892-1980) 7 first described this sign in 1938 5. Westermark was also an accomplished sailor and won a silver medal, as a member of the Swedish team, at the 1912 Olympics in Stockholm 7.
- 1. Sreenivasan S, Bennett S, Parfitt VJ. Images in cardiovascular medicine. Westermark's and Palla's signs in acute pulmonary embolism. Circulation. 2007;115 (8): e211. doi:10.1161/CIRCULATIONAHA.106.665422 - Pubmed citation
- 2. Osborn A, Blaser S, Salzman K. Encyclopedia of Diagnostic Imaging. AMIRSYS. (2008) ISBN:0721629059. Read it at Google Books - Find it at Amazon
- 3. Webb WR, Higgins CB. Thoracic Imaging. Lippincott Williams & Wilkins. (2010) ISBN:1605479764. Read it at Google Books - Find it at Amazon
- 4. E.Brant MW, A.Helms MC. The Brant and Helms Solution. Lippincott Williams &Wilkins. (2007) ISBN:B0011ZYZR2. Read it at Google Books - Find it at Amazon
- 5. Westermark N. On the roentgen diagnosis of lung embolism. Acta Radiol 1938;19:357‑72.
- 6. Lee DS, Vo HA, Franco A, Keshavamurthy J, Rotem E. Palla and Westermark Signs. Journal of thoracic imaging. 32 (4): W7. doi:10.1097/RTI.0000000000000253 - Pubmed
- 7. Z. V. Maizlin. Wonders of Radiology. (2010) ISBN: 9781449976453