Horseshoe lung (HL) is an extremely rare congenital pulmonary malformation in which a parenchymal isthmus connects the basal segments of both lungs across the midline. This anomaly is usually associated with other congenital cardiopulmonary malformations, most notably scimitar syndrome, a rare form of partial anomalous pulmonary venous return (PAPVR). The coexistence of HL and scimitar syndrome is particularly unusual and presents with variable clinical manifestations, ranging from asymptomatic incidental findings to severe respiratory and cardiac compromise during infancy or adolescence. We report the case of a ۱۵-year-old previously healthy boy who was admitted after a syncopal episode during sports activity at school. The episode was associated with palpitations, generalized weakness, and transient loss of consciousness. Initial physical examination revealed a cardiac murmur, and transthoracic echocardiography showed right ventricular enlargement with preserved systolic function, mild tricuspid regurgitation, and suspicion of anomalous pulmonary venous drainage. During referral to a tertiary hospital, the patient developed recurrent episodes of hemoptysis, leading to admission to the pediatric pulmonology ward. Chest radiography demonstrated a curvilinear vascular opacity in the right lower lung, mild right lung hypoplasia, and rightward displacement of the heart. Follow-up echocardiography confirmed right heart enlargement, anomalous drainage of two pulmonary veins into the inferior vena cava, a small patent ductus arteriosus, and mild pulmonary hypertension. CT angiography revealed partial anomalous pulmonary venous connection, systemic arterial supply from the abdominal aorta to the right lung consistent with intralobar sequestration, and the presence of a midline parenchymal isthmus characteristic of HL. A ventilation/perfusion scan further confirmed misperfusion of the sequestered segment. The patient initially underwent endovascular embolization of the abnormal systemic arterial supply. However, recurrent hemoptysis developed three weeks later, requiring surgical segmentectomy of the sequestered lung tissue. Subsequently, the patient was evaluated and prepared for corrective open-heart surgery to address the PAPVR. This case illustrates the clinical significance of HL associated with scimitar syndrome, a rare but important combination of congenital anomalies. Clinical presentation varies widely depending on the degree of lung hypoplasia, the extent of anomalous venous return, and associated cardiovascular defects. Advanced imaging techniques such as multidetector computed tomography and cardiac magnetic resonance imaging are essential for accurate diagnosis and detailed anatomical assessment. Management must be individualized, ranging from observation in mild cases to interventional or surgical procedures in patients with severe symptoms, pulmonary hypertension, or recurrent infections.
