A 24-year-old female with a history of Swyer-James-MacLeod syndrome presented with acute onset of pleuritic chest pain and was initially diagnosed with acute pericarditis. The 12-lead electrocardiogram demonstrated typical diffuse ST-segment elevation and PR-segment depression. Symptoms resolved rapidly with anti-inflammatory therapy consisting of ibuprofen and colchicine. After completing a 3-month course of the latter, her symptoms rapidly recurred. Workup, including labs and cardiac imaging consisting of a transthoracic echocardiogram and cardiac magnetic resonance imaging, was initially interpreted as normal. Re-review of her cardiac imaging revealed the patient had signs of a congenitally absent pericardium, including a “Snoopy Sign” on her posterior-anterior chest X-ray, which is characterized by levoposition of the cardiac silhouette, a lucent area between the pulmonary artery and aorta because of the presence of lung tissue, a lucent area between the base of the heart and the left hemidiaphragm, loss of the right heart border, a prominent pulmonary artery, and a flattened and elongated left ventricular contour. The patient had a cardiac computed tomography scan, which confirmed the diagnosis. In conclusion, a congenitally absent pericardium is a rare disorder, often undetected or misdiagnosed. There are characteristic findings on imaging such as a “Snoopy Sign” on a posterior-anterior chest X-ray, which can be easily missed because of its rarity. Our goal of this report is to educate health care providers about this rare disorder.
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