Systemic-to-Pulmonary Arterial Shunts Simulating Chronic Pulmonary embolism

A 53-year-old woman with a history of rheumatoid arthritis, pulmonary hypertension, severe bronchiectasis, and previous pulmonary embolism (PE) presented with a two-week history of worsening dyspnea. Given the clinical suspicion for recurrent PE and supportive electrocardiographic findings, CT pulmonary angiography (CTPA) was performed.

CTPA demonstrated an apparent filling defect within the left main pulmonary artery extending into the left lower lobe lobar artery, raising concern for PE. However, the presence of severe left lower lobe bronchiectasis, prominent systemic bronchial arterial supply, and a similar filling defect on prior CTPA examinations suggested that the finding represented a flow-related artifact caused by unopacified systemic blood entering the pulmonary circulation through systemic-to-pulmonary arterial anastomoses (SAPA).

A repeat CT examination was acquired with simultaneous enhancement of the pulmonary arterial circulation and the aorta, resulting in uniform vascular opacification and resolution of the apparent filling defect caused by unopacified systemic arterial inflow. This study demonstrated complete resolution of the previously observed filling defect, with no evidence of pulmonary embolism, confirming the initial finding as an artifact.
This case illustrates the importance of adequate aortic enhancement during CTPA to avoid pseudo-PE artifacts and the subsequent misdiagnosis of acute or chronic pulmonary embolism, which may result in unnecessary treatment. Careful optimization of contrast-enhancement timing is essential in patients with suspected systemic-to-pulmonary arterial anastomoses.