Cavographic vs. cross-sectional measurement of the inferior vena cava diameter before filter placement: are we routinely oversizing?

OBJECTIVE: A megacava (vena cava with a diameter of 28 mm or greater) requires a particular filter to avoid migration. However, caval morphologies are variable. As the inferior vena cava (IVC) usually adopts a circular geometry after a filter is inserted, this study aims (a) to classify caval geometry and orientation; (b) to compare discrepancy between anterioposterior projective diameter (PD) and circumference-based calculated diameter (CD) measurements on cross-sectional computed tomography (CT) images; (c) if a discrepancy exists, determine how often it can affect IVC filter selection.

METHODS: A total of 1503 patients were retrospectively reviewed. Caval morphology was classified. PD and CD were measured at infrarenal IVC. Differences between the PD and CD were assessed by the Wilcoxon signed-rank test or paired t test (if appropriate). The scatterplot of PD vs. CD was used to show whether one is consistently larger than the other.

RESULTS: The PD was significantly larger than the CD (22.3 ± 3.5 vs. 20.4 ± 2.8, p < 0.001). The caval morphologies were divided into five types. Type 1 was oval IVC oriented left-anterior-oblique to the horizontal line with an angle (n = 999, 66.5%), type 2 was round IVC (n = 49, 3.3%), type 3 was oval IVC with a vertical long axis (n = 8, 0.5%), type 4 was oval IVC with a horizontal long axis (n = 75, 5.0%), and type 5 was irregularly shaped IVC (n = 372, 24.7%).

CONCLUSION: Patients with round IVC are rare. Measurement of CD may be better to assess maximum IVC diameter compared with PD for the purpose of IVC filter placement.

KEY POINTS: • Five types of IVC orientation are described in this paper: type 1 (n = 999, 66.5%), type 2 (n = 49, 3.3%), type 3 (n = 8, 0.5%), type 4 (n = 75, 5.0%), and type 5 (n = 372, 24.7%). • The incidence of megacava (vena cava with a diameter of 28 mm or greater) measured on anterioposterior projective imaging may be overestimated. • As an IVC will adopt a circular geometry following filter placement, circumference-based calculated diameter may be an appropriate approach for caval size determination.