Mirror-image type III complete duplication of inferior vena cava: a distinct classification subtype or a variant of an existing one?

The article presents a case of duplication of the inferior vena cava detected as an incidental finding in a 62-year-old patient who underwent computed tomography of the chest and abdomen for rectal cancer. Imaging revealed duplication of the inferior vena cava, with the left trunk exceeding both the right trunk and the aorta-crossing trunk in diameter. Both trunks were formed by anastomosing common iliac veins. Duplication of the left renal artery and vein was also noted; the lower left renal vein drained directly into the left trunk of the inferior vena cava, which then joined the upper renal vein and crossed the aorta as a single trunk before merging with the right inferior vena cava. The further course of the inferior vena cava to the right atrium was anatomically normal. The currently existing classification of inferior vena cava duplication does not provide a definitive description for the variant identified in this patient, creating difficulty in formulation of the medical conclusion. The observed anatomy most closely corresponded to Type III duplication, in which the right trunk normally exceeds the left and the aorta-crossing trunk in diameter. Based on the radiologic features and morphometric measurements of the duplicated inferior vena cava trunks, we assume that this represents a rare mirror-image anatomic variant of Type III duplication, in which the left trunk has the greatest diameter. Scientific data review revealed two additional reports describing similar duplication cases (three previously reported patients in total). In one publication this variant was suggested as a Type IV duplication, whereas in another, classification was not provided. Whether this anatomical pattern should be considered an independent Type IV duplication or a mirror-image modification of Type III remains debatable and merits discussion from an anatomical nomenclature standpoint. However, larger patient samples would be required, which is challenging owing to the rarity of the present anatomic variant.