Citation, DOI and article data
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