A systemic arterial-pulmonary arterial shunt mimicking a pulmonary embolism on CT pulmonary angiogram

We report the case of a middle-aged woman on a background of severe respiratory disease who presented with hemoptysis. Investigations with CT pulmonary angiogram showed evidence of a large pulmonary arterial filling defect which was initially treated as a pulmonary embolism. However, despite being anticoagulated, she experienced ongoing hemoptysis. Further imaging several days later using aortic phase CT confirmed that the filling defect was a false positive; the artifact was due to retrograde filling from a systemic arterial-pulmonary arterial shunt and anticoagulation was stopped. Although PE is the most common cause of filling defects, this case suggests that in the setting of patients with chronic inflammatory parenchymal pulmonary disease, clinicians should consider alternative causes such as systemic arterial-pulmonary arterial shunts.