Tumor thrombus (also called intravascular tumor extension) can be defined as tumor extending into vessel; typically a vein, it occurs in a lot of malignancies like hepatocellular carcinoma, Wilms tumor, and others. 1 Tumor thrombus has been reported to demonstrate increase in fluorine-18 fluorodeoxyglucose (FDG) uptake that would differentiate it from the benign bland thrombus which would not take up FDG on positron emission tomography/computed tomography (PET/CT) scan. 1 We present a case of spindle cell sarcoma of right kidney whose baseline contrast-enhanced CT revealed a mass replacing the right kidney and right renal vein associated with thrombus in the inferior vena cava (IVC). 18 F-FDG PET/CT imaging was done that revealed an FDG-avid hypermetabolic malignant right renal mass with hypermetabolic IVC thrombus extending to the right atrium., Competing Interests: Conflict of Interest None., (World Association of Radiopharmaceutical and Molecular Therapy (WARMTH). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. ( https://creativecommons.org/licenses/by-nc-nd/4.0/ ).)