Portal vein confluence variants on contrast-enhanced CT: distribution, IMV-confluence distance, and novel patterns in...

To characterize portal vein (PV) confluence variants on contrast-enhanced CT, quantify the inferior mesenteric vein (IMV)-to-confluence distance by variant, and report previously undescribed configurations.

We first labeled variants using an extended 14-type scheme (Prado I-XII plus two new types XIII-XIV). For comparability with prior literature, these were then collapsed to three drainage categories (Thomson I/II/III: IMV → SV, true trifurcation at the SMV-SV junction, IMV → SMV) for distance analyses.

After recoding to three drainage categories, the distribution was Type I/II/III = 45.7% (91/199) / 19.1% (38/199) / 34.7% (69/199). Two additional, previously unclassified variants (Types XIII-XIV) were identified on CT in 5/199 patients (2.5%). One case (Type XII, dual IMV) could not be assigned to a single drainage category and was excluded from the three-group comparisons (N = 198). Median IMV-to-confluence distances differed: 17.9 mm (Type I; interquartile range [IQR] 13.3-23.0), 0.0 mm (Type II; IQR 0.0-0.0), and 5.0 mm (Type III; IQR 3.5-7.0) (Kruskal-Wallis χ² = 159.12, p < 0.001; N = 198). Group differences were tested with Kruskal-Wallis and Bonferroni-adjusted pairwise Mann-Whitney U; agreement was assessed with Cohen's κ and ICC(2,1).

Classic PV confluence types predominate, but rare/novel configurations are present. The association between IMV drainage route and IMV-to-confluence distance supports variant-aware preoperative CT review to inform operative planning and patient safety.