these benign cysts are located at the right cardiophrenic angle in 70% of cases , left cardiophrenic angle in 22% of cases and rarely in the posterior or anterior superior part of the mediastinum in 8% of cases ( 2 ) . most of pericardial cysts ( > 50% ) are asymptomatic ( 1 , 3 ) and have a benign natural course . some cysts have symptoms such as dyspnea , chest pain , or persistent cough . although it occasionally presents with symptoms related to compression of adjacent structures , pericardial cysts usually have no symptoms and are almost always diagnosed incidentally . in this case report , we describe a patient with a pericardial cyst . presentation and the course of illness were unusual and the cyst was one of the largest cysts that has been reported to date . pericardial cysts are not common and giant pericardial cysts are rare and only data of 12 cases were available from 2000 to 2014 in pubmed , and we will review available published articles in the literature . with improvement of technology and a 24-year - old man presented to the emergency department with dyspnea and persistent cough . in physical exam , no abnormality was found . there was no recent weight loss , cough , sputum production , exposure to tuberculosis , joint pain , or rash . chest x - ray showed a large opacity obscuring the right heart border ( figure 1 ) . his trans - thoracic echocardiogram showed an echo - lucent space next to the right atrium at the right cardiophrenic angle . the apical four - chamber view of the transthoracic echocardiogram showed an echolucent space next to the right atrium at the right cardiophrenic angle , consistent with a pericardial cyst . the right and left ventricular chamber size and function were normal , and there was no valvular heart disease then computed tomography ( ct ) was recommended . ct revealed no pleural effusions , and a large fluid collection at the right pericardial border ( figure 2 ) . extensive work - up for infectious and inflammatory causes , including blood cultures , viral antibodies , sputum acid fast bacilli s ( afb ) , ppd testing , and collagen vascular disease markers was negative . no fluid or pathologic finding was seen in the pericardium . on the right side and outside the pericardium , a huge pericardial cyst measuring approximately 13  8  5 cm in diameter was found and totally excised ( figures 3 and 4 ) . pericardial cysts are uncommon benign congenital lesions in the middle mediastinum ( 1 , 4 ) . most of the masses in the middle mediastinum ( 61% ) are cysts ( 1 , 5 ) . pericardial cysts and also bronchogenic cysts are the second most common masses after lymphomas ( 1 ) . other cysts in the mediastinum are bronchogenic ( 34% ) , enteric ( 12% ) , thymic and others ( 21% ) ( 1 , 4 ) . pericardial cysts ( or benign mesothelial cysts ) , are uncommon lesions that are often found incidentally . their formation may result from failure of fusion of one of the mesenchymal lacunae that form the pericardial sac ( 6 ) . on histologic examination , the cyst wall is composed of fibrous tissue lined by mesothelium , like normal pericardium , with mild chronic inflammation ( 6 ) . most of them are asymptomatic ( 50% - 75% ) and found incidentally during routine chest x - ray or echocardiography ( 2 ) . additional diagnostic methods include trans - thoracic echocardiography , ct scan and magnetic resonance imaging ( mri ) . contrast - enhanced ct scan has been the modality of choice for diagnosis and follow - up ( 3 ) . on ct scan , the pericardial cyst is thin - walled , sharply defined , and an oval homogeneous mass . the diagnosis usually is suspected following abnormal findings on chest radiography , showing bulging of the right heart border . additional diagnostic modalities that may find pericardial cysts include transthoracic echocardiography , ct , and mri of the chest ( 3 , 5 , 8) . twenty reported cases of pericardial cysts in literatures presented before the age of eighteen ( 1 ) , but most of the articles reported older patients . pericardial cysts are usually unilocular , smooth , and smaller than 3 cm in diameter ( 5 ) . cyst size varies from 2 to 28 cm ( 1 ) . in our patient , the cyst size was 13  8  5 cm in diameter that is one of the largest cysts we have found in the literature ( 9 ) ( table 1 ) . ct scan with contrast has been the diagnostic modality of choice to follow asymptomatic patients with pericardial cysts ( 1 ) . however , no studies have shown the superiority of contrast ct over mri and echocardiography for diagnosis or follow - up . on ct scan , pericardial cysts are thin - walled , sharp , oval homogeneous masses . their attenuation is slightly higher than water density ( 30 to 40 hu ) ( 2 ) . their enhancement with intravenous contrast is poor ( 2).the frequency of follow - up imaging has not been defined . if the patient is asymptomatic , serial echocardiography is enough , but if the patient is symptomatic or reveals an increase in the size of the cyst or has solid component in the cyst cavity in the serial follow - up , a cyst resection has been the most favored approach [ with thoracotomy or sternotomy or video - assisted thoracic surgery ( vats ) ] ( 3 , 5 ) . aspiration is another method , but one - third of the patients have shown recurrence . one literature review reported that about 30% of the patients had recurrence after percutaneous drainage at three years .