You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Westermark sign is seen in: and explain in detail?
Ans. (a) Pulmonary embolism Ref- Westermark sign is a sign of pulmonary embolus seen on chest radiographs. It is one of several described signs of pulmonary embolus on chest radiographs. Pathology The theory behind the sign is either obstruction of the pulmonary artery or distal vasoconstriction in hypoxic lung 3. In one study (PIOPED) this sign was present on ~10% of chest x-rays of patients with confirmed pulmonary embolus 2. Radiographic features Plain radiograph focal peripheral hyperlucency secondary to oligaemia resulting in a collapsed appearance of vessels distal to the occlusion 2-4 central pulmonary vessels may also be dilated 3 History and etymology The Swedish radiologist Nils Johan Hugo Westermark (1892-1980) 7 first described this sign in 1938 5. Westermark was also an accomplished sailor and won a silver medal, as a member of the Swedish team, at the 1912 Olympics in Stockholm 7. Differential diagnosis emphysema 2 CXR may be normal, or may show Focal oligemia of affected segment (Westermark sign Q) Dilated right descending pulmonary artery (Palla's sign Q) Wedge-shaped opacities above the diaphragm (Hampton's Hump Q) Small pleural effusion