Abstract
1219
Objectives: Segmental or lobar perfusion defects on a ventilation-perfusion scan can be due to both embolic and non-embolic etiologies. In some instances, further evaluation with cross sectional imaging is warranted to determine the underlying cause. The purpose of this study is to review some of the non-embolic causes of matched and mismatched perfusion defects on VQ scan.
Methods: A case series of three patients with matched or mismatched perfusion defects on VQ scan due to non-embolic causes were reviewed. Correlation was made with chest radiography and cross sectional imaging to determine the underlying etiology. Results: Three patients with non-embolic causes of perfusion defects on VQ scan were reviewed. The first, with small cell lung cancer resulting in compression of the left main pulmonary artery and a mismatched perfusion defect involving both the left upper and lower lobes. The second, with an endobrochial tumor obstructing the right lower lobe bronchus resulting in compensatory decreased perfusion to the right lower lobe. The third, with congenital right pulmonary artery agenesis with decreased perfusion to the entire right lung.
Conclusions: When reviewing a VQ scan, it is important to consider both embolic and non-embolic causes of perfusion defects. Correlation with the chest radiograph should be made and further evaluation with cross sectional imaging obtained when appropriate. Patients who have a massive pulmonary embolism are typically too unstable to undergo a VQ scan. Therefore, a unilateral lobar or whole lung perfusion defect should prompt further evaluation for a non-embolic cause, such as a compressing mass or a congenital anomaly. Mediastinal masses, such as bronchogenic carcinoma or lymphoma, are a common cause for pulmonary artery obstruction due to external compression. Additionally, endobrochial lesions which obstruct the bronchus can cause a ventilation defect with a compensatory decrease in perfusion to the corresponding lung segment resulting in a matched perfusion defect on VQ scan.