The importance of clinical suspicion in diagnosing pulmonary embolism: a case of false-positive high probability radionuclide perfusion lung scan.

: The accuracy of scintigraphic evidence of perfusion defects, even when classified as 'high probability' by matching with ventilation techniques or thoracic roentenograms is unsatisfactory when used without a pre-test clinical evaluation of probability. Although unusual, a complete or near-complete unilateral absence of perfusion in a lung with normal perfusion controlaterally must alert clinicians to the possibility of a false-positive result. In such instances, the administration of therapeutic dosages of fibrinolitic and antithrombotic agents (or even surgery) may lead to deleterious consequences. We report a patient with malignancy causing extrinsic narrowing of the pulmonary artery leading to a drastic impairment in the perfusion of an entire lung, compatible with, but not diagnostic of massive pulmonary embolism.