We present a case report of a nine-year-old asymptomatic girl with a large cystic lesion of the left hemithorax, occupying almost 80% of the left hemithorax, first believed to be a parasitic cyst that was operated and proved to be of parietal pericardial origin. Mediastinal cysts and pericardial cysts in particular are mostly discovered accidentally and so was the case with our patient. The diagnosis included not only clinical examination but also the utilization of computed tomography and magnetic resonance imaging. The only treatment for pericardial cysts is surgical excision and patients recover fully with no complication.
Keywords: Pericardial cyst; asymptomatic; diagnosis; size; surgical treatment.