Radiographic Characterization of Inferior Vena Cava and Its Reaction Following Filter Placement: A Single-Center Retrospective Study

Objective: To classify the radiographic characterization of the inferior vena cava (IVC) diameter, as well as to quantitatively describe the dimensional alternations in response to variations in filter placement, using cross-sectional computer tomographic venography (CTV) imaging. Methods: A single-center retrospective study was conducted on eligible patients who underwent CTV of IVC both before and after the placement of spindle-shaped filters, from September 2018 to June 2023. Baseline data, IVC diameter and orientation pre- and post-filter placement, IVC enlargement rate, and related complications were analyzed. Results: A total of 70 eligible patients were included, 52 (74.3%) with type 1 IVC, 11 (15.7%) with type 2, 4 (5.7%) with type 3, 3 (4.3%) with type 4, and none with type 5. An accompanying morphological alteration turned IVC into a quasi-round shape with Lin CCC of 0.870, and orientation was significantly altered after filter placement. In patients with type 1, 3, and 4 IVCs, the mean diameter of the IVC increased almost 1.5-fold in the minor axis (95% confidence intervals [CIs]=−7.77 to −5.83, p<0.001), while only a slight expansion of the major axis to its initial size ( p>0.05). Greater IVC enlargement rate was seen in the diameter of the minor axis than in the major axis (95% CI=40.31 to 65.12, p<0.001). Notably, regional clots around the filter were found in 22 (31.4%) patients. Among them, 14 (20.0%) were located on the anterior or posterior walls of caval minor axis, 5 (7.1%) in the lateral walls, and 3 (4.3%) in the central part of the IVC filter. Patients exhibited a higher incidence of clots on anterior and posterior walls compared to lateral wall (20.0% vs 7.1%, p=0.014). Conclusion: The morphology of IVC shifted toward an approximated as circles after filter placement, with greater diameter changes seen in the minor axis compared to the major axis, where filter-related thrombosis most occurs. Clinical Impact The findings of this study offer insights into the biomechanical interaction between the inferior vena cava (IVC) and spindle-shaped filters, highlighting the anisotropic dimensional changes triggered by filter placement. The pronounced expansion along the minor axis, where filter-related thrombosis was more frequently observed, underscores a previously underrecognized risk factor for post-implantation complications. These results indicate that perioperative optimization of IVC dimensions and vigilant post-placement monitoring are crucial for improving patient outcomes.