<prompt> Westermarks sign is seen in:Pulmonary embolismPulmonary sequestrationPulmonary alveolar proteinosisA.B.P.A Allergic Broncho-pulmonary Aspergillosis  <response>: Ans. a Pulmonary embolismRef: Harrison 19th ed. 1633Westermark sign is due to focus of oligemia in pulmonary embolism PE. The sign develops due to following reasons: Dilation of the pulmonary arteries proximal to the embolus Collapse of the distal vasculature creating the appearance of a sharp cut off on chest X rayThe chest x-ray is normal in the majority of PE cases, the Westermark sign is seen in 2 of patients 