Palla sign

Last revised by Craig Hacking on 10 Oct 2022

Palla sign is a sign seen on chest radiographs suggestive of pulmonary embolism, usually seen in the acute setting.

Although uncommon, it can be seen along with several other described signs of pulmonary embolus on chest radiography.

Palla sign describes an enlarged right descending pulmonary artery. When present with the Westermark sign, is suggestive of an occlusion of a lobar or segmental pulmonary artery, or widespread occlusion of small arteries.

The descending interlobar branch of the right pulmonary artery is enlarged, causing a "sausage" appearance towards right middle lobe of the chest radiograph.

The sign has a low sensitivity and its specificity is not known. 

The sign is named after Antonio Palla (1949-fl.2020), an Italian radiologist, who published his observations in 1983 that approximately 25% of patients with pulmonary embolism had an enlarged right descending pulmonary artery 1.

ADVERTISEMENT: Supporters see fewer/no ads

Cases and figures

  • Case 1: Palla and Westermark signs of acute PE
    Drag here to reorder.
  • Case 2: Palla sign of PE
    Drag here to reorder.