Left atrial myxoma arising from the left atrial appendage presenting with cardiorespiratory arrest in a neonate: a case report.

Introduction: Primary cardiac tumors are exceedingly rare in neonates, with rhabdomyomas predominating in this age group. While myxomas are the most common primary cardiac tumor in adults, they remain a clinical rarity in newborns and typically arise in the right atrium. We report an exceptional case of a left atrial myxoma originating from the left atrial appendage, associated with an unexplained cardiorespiratory arrest and imaging features consistent with a "ball-valve" mechanism, a presentation that, to our knowledge, has not been previously reported in the neonatal population. Case presentation: We report a male neonate whose postnatal course was complicated by intrauterine fetal distress and meconium aspiration syndrome. During recovery, the patient developed an unexplained cardiorespiratory arrest that prompted a transthoracic echocardiogram on day 20 of life. The study revealed a pedunculated, highly mobile left atrial mass with a long, thin pedicle arising from the lateral wall of the left atrium overlying the left atrial appendage. The mass prolapsed through the mitral valve during diastole, with imaging features consistent with high embolic risk. Urgent surgical resection was performed on day 25 of life via median sternotomy under cardiopulmonary bypass, together with closure of a concomitant patent ductus arteriosus. Histopathological examination confirmed cardiac myxoma. The postoperative course was favorable, and the patient was discharged hemodynamically stable. Conclusions: This case highlights an unusual neonatal left atrial myxoma arising from the left atrial appendage and detected after an unexplained cardiorespiratory arrest. Although a definitive causal relationship cannot be established, the tumor's marked mobility and mitral valve prolapse suggest that intermittent dynamic obstruction may have been a plausible contributing factor. This case adds valuable information to the limited literature on neonatal cardiac myxomas and supports early echocardiographic evaluation in neonates with unexplained cardiopulmonary collapse.