Westermark's and Palla's signs in acute and chronic pulmonary embolism: Still valid in the current computed tomography era.

Sir,

Pulmonary embolism is a dreaded complication of venous thrombosis that accounts for at least 300,000 deaths in the United States yearly.[1] Not many decades ago,[2] plain chest X-rays were a preferred non-invasive imaging modality to evaluate for pulmonary embolism. Careful analysis of plain x-rays in the appropriate clinical setting can occasionally yield classic radiologic signs described in the literature,[34] which may lead to confirmatory investigations.

A 62-year-old male with no significant medical history presented to the Emergency Department with progressive dyspnea on exertion for 3 weeks; on initial assessment, his vital signs were within normal limits. His physical examination was unrevealing. His chest X-ray [Figure 1] showed focal, demarcated oligemia in the upper right lung (circle, Westermark's sign), in contrast to a prominent right descending pulmonary artery (arrow, Palla's sign). Pulmonary embolism was strongly suspected, and the patient was started on intravenous unfractionated heparin. A computed tomography (CT) pulmonary angiogram was obtained, which confirmed the presence of extensive, saddle emboli at the right pulmonary artery [Figure 2], with eccentric shape, along with smaller thrombus on the left pulmonary artery, consistent with acute and chronic pulmonary embolism.

Figure 1

Chest x-ray on a PA projection that shows focal relative oligemia of the right upper lung (Westermark's sign, circle), in contrast to significantly dilated right descending pulmonary artery, with a “sausage-like” appearance (Palla's sign, arrow)

Figure 2

CT pulmonary angiogram, coronal view, maximum intensity projection (MIP) series, with evidence of a large sized, saddle pulmonary embolus at the right pulmonary artery (arrow), with eccentric appearance suggestive of chronic thromboembolism; there are also smaller filling defects on the left pulmonary artery (ellipse), consistent with acute emboli

The concurrence of Westermark's and Palla's signs has been reported in cases of acute pulmonary embolism;[5] we documented their presence in a patient with acute and chronic pulmonary embolism. Individuals with chronic hypoxemia, secondary erythrocytosis, and a positive Westermark's sign have a 2.3 times higher probability of being diagnosed with chronic pulmonary embolism, as compared to those in whom this radiologic sign is absent.[6] Despite the superior sensitivity of multi-slice CT angiogram for the diagnosis of acute and chronic pulmonary embolism, we should not neglect the diagnostic information provided by more modest techniques, including plain chest x-rays, as they continue to be the most common radiologic tests ordered in Emergency Departments around the world.