A difficult-to-diagnose pericardial fistula.

Pericardial fistula is a rare complication. Generally, the diagnosis can be confirmed by imaging examination, but our patient was an exception. We present a 71-year-old female patient that complained of remnant gastric cancer for five months and dyspnea for seven days; the dyspnea became aggravated during the last two days. After admission, emergency thoracic computed tomography and echocardiography showed pericardial effusion, and pericardiocentesis was performed. After conventional treatment, the pericardial effusion was unchanged and no cancer cells were found in the pericardial drainage. However, the color changed from turbid to golden yellow and, finally, to green. After 20 days of repeated laboratory, imaging, and gastrointestinal contrast examinations, no cause was found. Moreover, a clinical diagnosis could not be obtained following numerous comprehensive clinical analyses. Given the color change of the pericardial drainage, we strongly suspected pericardial fistula, but the imaging examinations were negative. Finally, a methylene blue test confirmed the existence of a pericardial fistula. When the color of the pericardial effusion changes, the existence of a pericardial fistula must be considered in advance, and other methods should be evaluated if imaging cannot assist in the diagnosis.