Interventricular Septal Blood Cyst Incidentally Discovered During Repair of Double-Chambered Right Ventricle in a Child

Blood cysts are rare benign intracardiac lesions predominantly observed in neonates and infants, most commonly arising from the mitral or tricuspid valves. Interventricular septal blood cysts are exceedingly rare, particularly in children and in association with double-chambered right ventricle (DCRV). A 3-year-old girl with DCRV was admitted for elective surgical repair. Preoperative transthoracic echocardiography demonstrated hypertrophied anomalous muscle bundles causing right ventricular outflow obstruction, without evidence of any intracardiac cystic lesion. During surgery, a previously undetected spherical bluish cystic lesion measuring approximately 2 cm was identified arising from the interventricular septum and protruding into the right ventricular cavity. The lesion was punctured intraoperatively, yielding blood-filled contents without daughter cysts or membranous material. Because of the proximity of the lesion to the interventricular septum and potential risk to the conduction system, complete excision was avoided. The cyst was aspirated and decompressed, followed by successful DCRV repair. The postoperative course was uneventful, with no rhythm disturbances or evidence of recurrence on short-term follow-up. Interventricular septal blood cysts are extremely rare intracardiac lesions that may remain occult on routine preoperative imaging. This case highlights the diagnostic challenges associated with unusual intracardiac cystic lesions in children and demonstrates that conservative surgical management may be appropriate when lesions are located near the cardiac conduction system.