Marantic Endocarditis Presenting With Ischemic Stroke in Advanced Non-small Cell Lung Cancer: The Contribution of Fluorodeoxyglucose (FDG) PET/CT to the Differential Diagnosis of Valvular Vegetations

Non-bacterial thrombotic endocarditis (NBTE), also known as marantic endocarditis, is an uncommon complication of advanced malignancy and an important cause of systemic embolism. Differentiating NBTE from infective endocarditis (IE) can be challenging because echocardiographic findings may be similar, while microbiological investigations remain negative. We report the case of a 66-year-old man with metastatic non-small cell lung cancer (NSCLC) who presented with multifocal ischemic stroke. Transthoracic and transesophageal echocardiography identified an 8.5 mm vegetation on the posterior mitral leaflet. Repeated blood cultures and an extensive evaluation for culture-negative IE were negative. Fluorodeoxyglucose (FDG) PET/CT demonstrated progression of the underlying malignancy but showed no abnormal uptake at the level of the cardiac valves. When interpreted together with the clinical and microbiological findings, these results supported the diagnosis of NBTE after exclusion of IE. This case highlights the potential contribution of FDG PET/CT as part of a multimodal diagnostic approach for differentiating sterile from infective valvular vegetations in patients with advanced cancer.