Prenatal diagnosis of mitral–pulmonary intervalvular fibrosa pseudoaneurysm associated with TGA causing severe pulmonary stenosis: A rare case report

Pseudoaneurysm of the mitral–aortic intervalvular fibrosa is a rare and typically acquired cardiac lesion, with congenital forms being exceptionally uncommon, particularly when identified prenatally. We report the case of a 23-year-old gravida 2 woman with one previous history of miscarriage who was referred at 25 weeks' gestation for a fetal intracardiac mass. Fetal echocardiography revealed a cystic echogenic mass at the crux of the heart, consistent with a pseudoaneurysm arising from the mitral-pulmonary intervalvular fibrosa (MPIVF) associated with transposition of the great arteries, causing severe left ventricular outflow tract obstruction or subvalvular pulmonary stenosis. The cardiac lesion was also associated with a large mid-muscular ventricular septal defect alongside a small left ventricle suggestive of single-ventricle physiology. This constellation of findings pointed to a diagnosis of complex cyanotic congenital heart disease with possible ductal-dependent pulmonary circulation. Prenatal diagnosis enabled early parental counseling, planning for delivery at a tertiary cardiac center, and postnatal preparation for prostaglandin therapy and surgical evaluation. This case highlights the importance of recognizing MPIVF pseudoaneurysm in the fetal period, particularly when associated with obstructive physiology or major structural anomalies, and contributes to the limited literature on congenital variants of this condition. Learning objective Pseudoaneurysm of the mitral–pulmonary intervalvular fibrosa is an exceptionally rare congenital lesion. Its association with transposition of the great arteries, ventricular septal defect, and left ventricular outflow tract obstruction has important prognostic and surgical implications. Prenatal echocardiography is key for recognition, particularly when there is a cystic or echogenic intracardiac mass with a to-and-fro Doppler flow near the atrioventricular junction. Prenatal echocardiography is crucial for early counseling and planned delivery at a tertiary cardiac center.

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