Compressive Large Diaphragmatic Mesothelial Cyst Mimicking a Pericardial Cyst in a Patient With Exertional Dyspnea

BACKGROUND: Diaphragmatic mesothelial cysts are rare and can be misdiagnosed as pericardial cysts. These cysts are usually asymptomatic but can cause symptoms because of compression on adjacent structures. CASE SUMMARY: A 63-year-old man presented with exertional shortness of breath. Echocardiography showed a pericardial cyst adjacent to the right heart, and stress single photon emission computed tomography was negative for ischemia. Computed tomography (CT) and magnetic resonance imaging (MRI) demonstrated a large pericardial cyst adjacent to the right coronary artery with compression on the right atrioventricular groove. He underwent surgery, which revealed a mesothelial cyst embedded in the diaphragmatic muscle. DISCUSSION: Mesothelial cysts rarely can be misdiagnosed as pericardial cyst and can cause chest pain and shortness of breath from compressive effects. Echocardiography is usually the initial step for assessment, followed by a CT scan or an MRI, which provide more anatomical details. Surgery can be considered in symptomatic patients. TAKE-HOME MESSAGES: Mesothelial cysts are usually diagnosed incidentally on echocardiography, CT, or MRI. Compressive effects occur rarely with diaphragmatic mesothelial cysts and can mimic compressive pericardial cysts.