Isolated Epicardial Langerhans Cell Histiocytosis in a Neonate With Complete Spontaneous Regression

Langerhans cell histiocytosis (LCH) is a rare clonal myeloid neoplasm. Cardiac involvement is exceedingly uncommon in neonates. We report a term male neonate with prenatally detected pericardial effusion and a postnatally identified epicardial mass adherent to the left ventricle. Multimodal imaging demonstrated confinement to the visceral pericardium without myocardial infiltration. Biopsy confirmed LCH (CD1a⁺, CD207⁺, S-100⁺, ALK^-, BRAFV600E^-) and staging excluded systemic disease. The patient remained hemodynamically stable and was managed conservatively after multidisciplinary evaluation. Serial imaging demonstrated complete spontaneous regression by 6 months. Comprehensive staging and precise anatomical imaging can guide safe observation in isolated epicardial LCH.