CONCLUSION:
Although pericardial effusion is rare as the first demonstration of pediatric mediastinal lymphoma, it is important to take this differential diagnosis into consideration. Because non-Hodgkin lymphomas with mediastinal disease at presentation have a natural tendency for rapid dissemination and worse prognosis when invading the pericardium, hence minimal delay in diagnosis is essential to avoid incorrect initial management and initiate the true approach as soon as possible.