Portal supply of segment IV of the liver based on CT-scan

Background The portal vascularization of segment IV (S4) of the liver has not been well described. Knowledge of the portal supply to S4 is of great interest for liver surgery and for interventional radiological procedures. This study aimed to analyse the distribution of portal vein branches supplying S4. Methods We retrospectively analysed data from patients operated on for liver tumours between 2007 and 2016. Patients with involvement of S4 branches or the left portal vein, previous liver surgery or poor quality imaging were excluded. Branches originating from the right portal vein and/or from the transverse part of the left portal vein (TPLPV) and/or from the umbilical part of the portal vein (UPLPV) were identified. Results In 102 patients who underwent a right hepatectomy, S4 was vascularized by 2–8 branches of the left portal vein, with 84.3 % of patients having 3–6 branches. Only eleven patients (10.8 %) had portal branches originating from the TPLPV, with no impact on the number of branches coming from the UPLPV. Three patients (2.9 %) had one branch from the right portal vein. In patients with only two or three branches supplying S4, the branches had a larger diameter and typically arose from a short common trunk which divided further within its first centimetres. Conclusions Portal vascularization of S4 varies widely (2–8 branches) between patients and originates predominantly from the junction between the left portal vein and the round ligament. There is no anatomical rationale to divide S4 into S4a and S4b.