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.