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Chicken on a fence sign: Pericardial effusion

A chest X-ray is often normal in patients with a pericardial effusion as an increased cardiothoracic ratio only occurs with effusions exceeding 300 ml. Despite this there remains a role for chest x-ray – for example the European Society of Cardiology still recommends performing a chest X-ray for any patient with a suspected pericardial effusion. The ‘chicken on a fence’ sign has been used in the literature on one occasion to describe the appearance of a pericardial effusion on a chest radiograph. The ‘fence’ outlines the diaphragm and the chicken is the enlarged cardiomediastinal silhouette. This is more commonly referred to as the waterbottle sign, a description that was in use by 1946. Although X-ray is often the initial imaging modality, cross-sectional studies including echocardiography and CT provide greater accuracy in assessing the heart, pericardium and lungs for pathology.