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Background
Several signs suggestive of pulmonary embolism have been described in literature on chest radiography. Most common of these include Hampton’s Hump, Fleischner Sign (Pulmonary Embolism), Westermark Sign, Palla Sign, and Knuckle Sign. Taking into account typical signs/symptoms of pulmonary embolism (e.g., dyspnea, chest pain, tachycardia) recognition of these signs can serve valuable in the correct clinical context. This exhibit will seek to educate on recognition of image findings pertaining to these signs through a case based approach using everyday chest radiographs and corresponding CT-PA images.

Educational Goals / Teaching Points
Define 5 common signs suggestive of a pulmonary embolism on everyday chest radiographs. Recognize which of these signs are present in a series of everyday cases with confirmed pulmonary embolism. Describe imaging characteristics of these signs on everyday chest radiographs and corresponding CT-PA images. Recognize the limitations of these signs.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The following signs of PE will be presented in a case based review. The imaging characteristics of each sign will be highlighted and described on the corresponding chest radiographs and CT-PA images. Hampton’s Hump, peripheral wedge-shaped, pleural-based opacification with apex pointing to the hilum. Fleischner Sign (Pulmonary Embolism), overtly prominent central pulmonary artery silhouette. Distention of the main pulmonary artery secondary to a large pulmonary embolus. Westermark Sign, focal peripheral hyperlucency overlying a lung distribution secondary to oligemia. Obstruction of a pulmonary artery leads to a hypoxic region of lung with decreased vascular markings. Palla Sign, “Sausage” appearance to a descending interlobar pulmonary artery branch, typically right sided. Knuckle Sign - Abrupt tapering and/or cutoff of the right or left main pulmonary artery branch.

Conclusion
Several signs on everyday chest imaging are suggestive of pulmonary embolism. It is important to recognize that signs alone are not pathognomonic. Chest radiography is neither sensitive nor specific for a pulmonary embolism. While essential in the investigation of suspected PE, their main value is to exclude diagnoses that clinically mimic PE. Ultimately, it is essential to interpret any sign with awareness to the clinical presentation. Taking into account typical signs/symptoms of pulmonary embolism (e.g., dyspnea, chest pain, tachycardia) recognition of these signs can serve valuable in the correct clinical context.