Acute pulmonary embolism and Palla’s sign

A 41-year-old woman presented to the emergency department with acute onset difficulty breathing for 1 day. Three days before, she underwent hysterectomy for symptomatic fibroid in another hospital. On examination, the blood pressure was 110/70 mmHg, the pulse was 114 per minute, respiratory rate was 30 per minute and oxygen saturation was 96% with low-flow oxygen supplementation through a venturi mask. Auscultation of the chest was normal. The chest radiograph showed an enlarged right descending pulmonary artery with a ‘sausage’ appearance suggestive of Palla’s sign of pulmonary embolism (Figure 1A). Electrocardiography revealed an S1Q3T3 pattern, i.e. prominent S wave in the lead I and a Q-wave and T-wave inversion in the lead III (Figure 1B). Subsequently, a computed tomographic pulmonary angiography revealed hypodense filling defects suggesting embolism in the distal left pulmonary artery near its branching (Figure 1C). She improved with anticoagulation therapy and discharged. The conventional radiographic features of pulmonary embolism include a triad of Palla’s sign, Westermark’s sign and Hampton’s hump.1 Palla’s sign describes an enlarged right descending pulmonary artery with a peculiar appearance of ‘sausage’ or ‘irregular cone’ toward the right middle lobe in the radiograph. The enlargement and abnormal shape of the artery attribute to the rapid increments in transmural pressure resulting from acute occlusion of the inferior pulmonary vascular bed, leading to dilatation of the upstream segment.2 Focal oligemia in the area supplied by the thrombosed pulmonary artery is known as Westermark’s sign. Hampton’s hump is a peripheral wedge-shaped density above the diaphragm resulted from pulmonary infarction distal to the obstruction.1