Clinical data for each patient are shown in Table 1. The median age at KPE was 62.7 days (range 31–108 days). Six patients were native liver survivors, and the remaining four patients underwent liver transplantation. All parameters of the preoperative blood tests were not significantly different between the LT group and the NLS group [CRP value, LT group vs. NLS group: 0.13 (0.05–0.22) vs. 0.12 (0.07–0.58), p = 1.00] [WBC, LT group vs. NLS group: 11,210 (8890–14850) vs. 10,550 (5800–13090), p = 0.762] [d-bil, LT group vs. NLS group: 4.85 (2.6–6.7) vs. 3.95 (2.5–8.0), p = 0.915] [ALT, LT group vs. NLS group: 65.0 (29.0–146) vs. 54.5 (20.0–104), p = 0.762] [γ-GTP, LT group vs. NLS group: 328 (111–547) vs. 344 (229–1094), p = 0.61].

Representative histopathological findings of the biopsy liver specimens are shown in Fig. 1. Figure 1a shows double immunohistochemistry for CD31 and D2-40 counterstained with hematoxylin while Fig. 1b shows EMT staining.

Representative histopathological findings of biopsy liver specimens. a CD31/D2-40; yellow arrow, portal vein. b Elastica-Masson Trichrome; yellow arrow, fibrotic area. c Hepatitis-Like findings; yellow arrow (top row), acidophilic body; yellow arrow (bottom row), hepatocyte multinuclear change

There were no significant differences in the number of portal vein branches, portal vein diameters, and fibrosis area at KPE between the left and right liver specimens [number of portal vein branches, left vs. right: 28 (21–58) n/mm2 vs. 25 (17–34) n/mm2, p = 0.405] [portal vein diameters, left vs. right: 6.7 (6.4–8.0) μm/n vs. 7.1 (5.8–7.9) μm/n, p = 0.705] [fibrosis area, left vs. right: 22.8 (18.8–27.2) % vs. 19.7 (14.4–22.8) %, p = 0.326].

There was no significant correlation between the age at KPE and the left-to-right ratio of the number of portal vein branches, portal vein diameters, or fibrosis area (age at KPE vs. ratio of number of portal vein branches [left/right]: r = 0.322, p = 0.364) [age at KPE vs. ratio of portal vein diameters (left/right): r = − 0.073, p = 0.841] [age at KPE vs. ratio of fibrotic area (left/right): r = 0.286, p = 0.424].

No significant difference in the portal vein morphology was observed between LLS and RAS, regardless of KPE age.

Representative HLF of the biopsy liver specimens are shown in Fig. 1c. The HLF scores in the LLS and RAS of each patient are shown in Fig. 2. There tended to be a positive correlation between the HLF score and age at KPE, although the difference was not statistically significant, for LLS (r = 0.590, p = 0.072) and RAS (r = 0.622, p = 0.055). The LLS scores were always higher than or equal to those of the RAS, and there was no single case where LLS was lower.

Hepatitis-like findings in the left and right liver in each patient. Rt. HLF, light color; Lt. HLF, dark color. Patients; large bold, liver transplantation. Age at KPE (day); KPE, Kasai portoenterostomy

Representative findings of lymphatic vessel morphology in the biopsy liver specimens are shown in Fig. 3. Histopathological findings in non-BA patients showed that lymphatic vessels are usually localized in the portal area (Fig. 3a). The histopathological findings of LLS (Fig. 3b) and RAS (Fig. 3c) in BA patients indicate that lymphatic capillaries proliferated into porto-portal bridging fibrosis. The correlation between the fibrotic area of all specimen areas and the number of lymphatic vessels is shown separately in the LLS and RAS in Fig. 4. This result showed a positive correlation between LLS (r = 0.571, p = 0.084) and RAS (r = 0.681, p = 0.030). The correlation between the age at KPE and the left-to-right ratio of the number of lymphatic vessels is shown in Fig. 5. Additionally, the correlation between pre-KPE CRP value and the left-to-right ratio of the number of lymphatic vessels with lumen is shown in Fig. 6. These results showed a significantly positive correlation (r = 0.723, p = 0.018) and revealed that the LLS/RAS lymphatic vessel ratio increases with an older age at KPE and with the pre-KPE CRP value.

Representative findings of the lymphatic vessel morphology in biopsy liver specimens. a Non-BA, 2 years-old patient with choledochal cyst; b BA, left lateral segment; c BA, right anterior segment. Yellow arrow, lymphatic vessels with lumen; Red arrow, lymphatic vessels without lumen

Correlation between the fibrosis area of all specimen areas and the number of lymphatic vessels in the LLS and RAS, separately. a LLS, left lateral segment; vertical axis, fibrotic area (%); horizontal axis, lymphatic vessels. b RAS, right anterior segment; vertical axis, fibrotic area (%); horizontal axis, lymphatic vessels

Correlation between age at KPE and the left-to-right ratio of the number of lymphatic vessels. Vertical axis, ratio (left/right); horizontal axis, age at KPE (day)

Correlation between pre-KPE CRP value and the left-to-right ratio of the number of lymphatic vessels with lumens. Vertical axis, lymphatic vessels ratio (left/right) without lumen; horizontal axis, pre-KPE CRP value(mg/dL)