n engl j med 366;11 nejm.org march 15, 2012 e16 A 47-year-old woman presented to the emergency department with acute shortness of breath and hypoxemia. Her medical history included sex reassignment, for which she was taking estrogen, and a deep-vein thrombosis on the left side, for which she had required treatment with warfarin. She had a family history of fatal pulmonary emboli. An electrocardiogram revealed right bundlebranch block and right axis deviation (the electrocardiogram is available in the Supplementary Appendix). Blood tests revealed an elevated d-dimer level of 2073 ng per milliliter. A chest radiograph showed a Westermark sign (Panel A, arrow), with a focal area of oligemia in the right middle zone and cutoff of the pulmonary artery in the upper lobe of the right lung. Computed tomographic pulmonary angiography confirmed the presence of a thrombus in the right pulmonary artery (Panel B, arrow), with an occlusive thrombus in the pulmonary arteries of the right upper and middle lobes. Another thrombus could be seen in multiple branches of the left pulmonary artery. The patient was given warfarin and made a good recovery.