Lung Perfusion SPECT: Application in a Patient with Tetralogy of Fallot and Suspected Pulmonary Thromboemboli

A 22-year-old woman presented with acute left-sided pleuritic chest pain and dyspnea 6 days after surgery for revision of the stenotic central aortopulmonary shunt. She had a history of tetralogy of Fallot (TOF), pulmonary valve stenosis, ventricular septal defect and major aortopulmonary collateral artery. Her Waterston shunt was placed when she was 5 years old and stented and re-dilated after stenosis. Acute pulmonary thromboemboli (PTE) was suspected and pulmonary perfusion scan was performed with 4 mCi 99m Technetium labeled macroaggregated albumin. The left lung was globally hypoperfused with evident uptake in the brain, renal parenchyma and thyroid. SPECT images revealed a segmental wedge-shaped peripheral defect in the posterior segment of the left upper lobe. The scan was interpreted as acute/chronic PTE or vascular abnormality. CT angiography excluded PTE; nevertheless the patient was treated with a therapeutic dose of heparin changed to warfarin and was discharged with improvement of the symptoms. Pulmonary artery angiography was not performed.