A pulmonary metastasis from renal cell carcinoma seen on a lung perfusion scan

A 75-year-old man with known pulmonary metastases from renal cell carcinoma had ventilation and perfusion scans to rule out a pulmonary embolism. The ventilation scan showed a round defect at the left lung base. The Tc-99m MAA perfusion scan revealed multiple areas of increased tracer activity, at least one of which corresponded to the patient's pulmonary metastases seen on chest radiograph. The most plausible explanation for this finding was that the tumor metastasis invaded the pulmonary artery causing shunting of the tumor vessels with the pulmonary artery.