Merkel cell carcinoma cardiac metastasis causing cardiac tamponade.

We describe an unusual presentation of Merkel cell carcinoma (MCC), a rare neuroendocrine cutaneous tumour. A 59-year-old man presented with a 2-week history of dyspnoea on a background of MCC of the left elbow that was diagnosed after an axillary lymph node metastasis had appeared. He was clinically diagnosed with cardiac tamponade and received urgent pericardiocentesis. Thoracic CT imaging revealed a large infiltrating mass within the inferior aspect of the heart, confirmed to be MCC via immunohistochemistry of the pericardial fluid. On review of prior fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) imaging, avid uptake was evident at the corresponding site of disease. This case has several important illustrative aspects, including the clinical manifestations of cardiac metastases, the challenges of MCC histopathological diagnosis and the role of imaging (in particular FDG-PET) in this aggressive disease.