Massive pulmonary embolism without symptoms demonstrated by radionuclide imaging with thromboemboli in both main pulmonary arteries.

Massive pulmonary embolism is defined as an anatomic obstruction of 50% or more of the pulmonary artery. A reduction of at least 50% of the cross-sectional area of the pulmonary artery causes significant hemodynamic instability and marked hypoxia exhibiting syncope, apprehension, hypotension, diaphoresis, chest pain, altered mental status, and shortness of breath. A patient, who had no definite clinical signs and symptoms, was demonstrated to have massive pulmonary embolism by extensive mismatched ventilation-perfusion defects scintigraphically and confirmed as thromboemboli in the main pulmonary arteries on a standard CT of the thorax. The lack of clinical manifestations of massive pulmonary embolism might be related to the insidious onset and progressive formation of thromboembolism. The patient gradually adapted to and/or compensated for hemodynamic changes.