[Hypoxemia secondary to inferior vena cava return into left atrium]

The case of a right-to-left shunt-induced hypoxemia with an abnormal return of the inferior vena cava (AIVCR) into the left atrium (LA) is reported in a 30-year-old male with cyanosis and polycythemia. The chest X ray and the lung CT scan was normal. Spirometry was normal but the transfert-CO coefficient (KCO) was lowered. Hypoxemia was observed at rest and worsening during exercise. The alveolo-arterial oxygen tension difference under hyperoxia was increased (56 kPa). Contrast echocardiography (CEch) suggested the presence of an AIVCR with a right-to-left shunt only observed by the inferior route. The inferior vena cava (IVC) angiography and the magnetic resonance imaging demonstrated an AIVCR characterized by a direct drainage of IVC in the left atrium. The good tolerance can be explained by the association of AIVCR with an inter-auricular septal defect resulting in a left-to-right shunt which partially corrected the right-to-left shunt. After surgical treatment, arterial blood gases normalized, KCO remained low and CEch became negative.