Unmasking of Agenesis of Right Pulmonary Artery with Unilateral Absence of Perfusion on Lung Scintigraphy.

We present a rare finding on lung ventilation-perfusion (V/Q) scintigraphy for a woman with longstanding dyspnea. CT of the chest showed volume loss on the right side, which raised concern about possible bronchiolitis obliterans or Swyer-James-MacLeod syndrome; however, the right pulmonary artery could not be visualized. A subsequent V/Q scan showed absence of perfusion and decreased ventilation to the entire right lung, consistent with agenesis of the right pulmonary artery. The patient's clinical course and imaging features mimicked Swyer-James-MacLeod syndrome, which usually presents with a matched perfusion defect in a single lung or lobe on V/Q scanning. This case highlights the importance of a multimodality imaging approach to achieve a diagnosis.