A phantom tumour of the lung in a patient with heart failure was misdiagnosed as a lung mass.

A phantom or vanishing tumour of the lung is an uncommon radiographic finding, often linked to fluid overload conditions such as heart failure or chronic kidney disease. It is characterised by the presence of interlobular effusion within the transverse or oblique fissure of the right lung. Despite its infrequency, it is a significant differential diagnosis for radiographic opacities in the right middle lung zone, given its potential to mimic more ominous pathologies such as neoplastic masses or infiltrative processes.In this report, we present a case involving a man in his 70s who presented with a 10-day history of productive cough, chest pain and shortness of breath. An initial chest X-ray (CXR) showed a well-defined, dense, round mass in the right lower lobe. An echocardiogram revealed a significantly reduced left ventricular ejection fraction. Following the initiation of loop diuretics and fluid restriction, the mass-like opacity completely disappeared on follow-up CXR after 7 days, confirming the diagnosis of a vanishing tumour. This case highlights the critical importance of addressing the underlying heart failure prior to considering further invasive diagnostic procedures, as this can help avoid unnecessary, expensive, and potentially harmful interventions.