4D flow MRI for the evaluation of venous anatomy and flow in renal cell carcinoma with venous tumor thrombus: a pictorial essay.

Renal cell carcinoma (RCC) is frequently associated with venous tumor thrombus (RCC-TT), which occurs in 5-20% of patients and significantly impacts surgical management. While CT and MRI provide excellent anatomic characterization, they offer limited insight into venous hemodynamics and venous collateralization, which are critical for operative planning in RCC-TT cases. Four-dimensional (4D) flow MRI is a time-resolved technique that enables simultaneous assessment of vascular anatomy and blood flow dynamics. In this pictorial essay, we illustrate the application of 4D flow MRI in RCC-TT across a spectrum of tumor thrombus levels. Through representative cases, we demonstrate how 4D flow imaging provides value over conventional imaging by clarifying vessel patency, flow directionality, and the presence and extent of collateral pathways. These insights are particularly relevant in determining whether the inferior vena cava (IVC) is functionally occluded, assessing redistribution of venous return, and anticipating tolerance to surgical maneuvers such as IVC cross-clamping, ligation, or resection. Our experience highlights that 4D flow MRI can reveal complex and variable patterns of venous drainage that are not readily apparent on standard imaging. By integrating hemodynamic information with anatomic findings, 4D flow imaging may enhance preoperative assessment and support surgical decision-making in patients with RCC-TT.