Pulmonary arteriovenous fistula in a rare location: The importance of excluding patent foramen ovale.

A 46-year-old woman with a history of repeated thromboembolic stroke and anti-phospholipid antibody syndrome was referred to our hospital. Saline contrast transthoracic echocardiography showed that microbubbles appeared in the left atrium within 4 heartbeats. Thus, she was initially suspected as having a patent foramen ovale with associated paradoxical embolism. However, no evidence of patent foramen ovale or atrial septal defect could be found using transesophageal echocardiography. Saline contrast transesophageal echocardiography showed that microbubbles flowed into the left atrium through the left superior pulmonary vein. Ultimately, she was diagnosed as having a pulmonary arteriovenous malformation located at the upper left pulmonary lobe using contrast computed tomography and pulmonary artery angiography. Pulmonary arteriovenous malformations are typically located in the lower lobe of either lung and, in bubble studies, contrast appears in the left atrium after 4 heartbeats. Here, the pulmonary arteriovenous malformation was in the upper lobe, and contrast appeared in the left atrium at an earlier time point: one associated with patent foramen ovale. These findings made it difficult to differentiate the two diseases initially. This case suggests that pulmonary arteriovenous malformation should be carefully considered, even if microbubbles appear in the left atrium early on a saline contrast transthoracic echocardiograph. Learning objective: Pulmonary arteriovenous malformation occasionally appears in the upper lobe. In these cases, microbubbles may appear in the left atrium after detection in the right atrium with a time-course that is suggestive of a patent foramen ovale. Therefore, diagnosis should be carefully confirmed by using other multimodal imaging tests, such as transesophageal echocardiography, contrast computed tomography, or pulmonary artery angiography.