Palla sign

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.

Pathology

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.

Radiographic features

Plain radiograph

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. 

History and etymology

The sign is named after Antonio Palla (1950-), 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.