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.