Table 1.
Details of the three cadavers.
Fig 1.
Distribution of lymphatic vessels in hepatic veins.
Vessels were stained for podoplanin and CD31 in 5 μm sections and were assessed by light microscopy. (A) Inferior vena cava. (B) Hepatic vein. (C) Sublobular vein. (D) Central vein. Lymphatic vessels (arrowheads) were present in the adventitia and intima of the inferior vena cava, in the adventitia of hepatic veins and in some sublobular veins that had a wall thickness greater than 110 μm. Lymphatic vessels were not observed in central veins or most other sublobular veins. Scale bars: 100 μm (A, B); 50 μm (C, D).
Fig 2.
Continuity and density distribution of lymphatic vessels from hepatic veins to the inferior vena cava.
Vessels were stained for podoplanin and CD31 and assessed as en-face whole-mount preparations by stereomicroscopy. (A) Peripheral portion: lymphatic vessels with blind ends were observed (arrowhead). (B) Proximal portion: lymphatic vessels were mainly continuous and became more abundant in the area where the hepatic veins were more centrally located. (C) Main trunk of the hepatic vein: lymphatic vessels were observed all around the wall of the main trunk. (D) Border between the inferior vena cava and the right hepatic vein: the lymphatic vessels of the main trunk of the hepatic vein were continuous with those of the inferior vena cava (the border is indicated by a perforated line), forming a rich lymphovascular network. The blind ends of lymphatic vessels were also observed in the proximal portion and the main trunk of the hepatic vein (B-D). Scale bars: 1 mm.
Fig 3.
Distribution rate of lymphatic vessels in each portion of the hepatic vein.
The distribution ratio of lymphatic vessels area was defined as the ratio of the podoplanin-positive area to total vein wall area. The distribution ratio increased from the peripheral portion (0.03%) to the proximal portion (0.22%) and to the main trunk (1.01%). *p = 0.012. **p = 0.0074. ****p<0.0001. Abbreviation: LVA/VA = ratio of lymphatic vessels to total area of hepatic vein wall.
Fig 4.
Correlation between density distribution of lymphatic vessels and hepatic vein diameter.
Correlations were calculated using proximal and main trunk portions only, as few lymphatic vessels were present in the peripheral portions. The Spearmann’s rank correlation coefficient between the diameter of the hepatic veins and the distribution rate of lymphatic vessels (LVA/VA ratio) was calculated. The distribution ratio of lymphatic vessels increased significantly as the diameter of the hepatic veins became larger. (Rs = 0.67, p<0.001). Abbreviation: LVA/VA = ratio of lymphatic vessels to total area of hepatic vein wall.
Fig 5.
The distribution of lymphatic vessels and India ink in the hepatic veins (Immunohistochemistry for podoplanin and CD31).
The uppercase letters show a magnified view of the area of the arrowhead in lowercase. a, A; central vein: India ink was observed in the perivascular space and in the interstitium of the central vein wall (arrow) b, B; sublobular vein: India ink was observed in the perivascular space and in the interstitium of the sublobular vein wall (arrow). c, C; sublobular vein with lymphatic vessel: India ink was present in the lymphatic vessels (arrowhead) of the sublobular veins. Scale bars: 50 μm (b, B), 100 μm (a, A, c, C,). d, D: hepatic vein. e, E; Vena Cava inferior. India ink was also present in the lymphatic vessels (arrowhead) of the hepatic veins and Inferior vena cava. f; Indian ink injection point: India ink injected into the liver parenchyma flowed into sinusoids and the Gleason’s sheath. Scale bars: 100 μm (d, D, e, E), 500 μm (f).
Fig 6.
Fig 7.
Schema of lymphovascular networks from the central vein to the inferior vena cava.
A: central vein B: sublobular vein C: peripheral portion D: proximal portion E: main trunk F: inferior vena cava. Some of the lymphatic fluid derived from the space of Disse flows towards the central vein (A). The lymphatic fluid runs through the perivascular space (represented by green perforated lines) of the central vein and sublobular vein as an extravascular fluid pathway. Secondarily, it enters the interstitium of the vein through the small pores of the cribriform structure of the veins. And then, lymphatic fluid enters the lymphatic vessels of the peripheral portion of the hepatic veins (C). Most of the lymphatic fluid flows through the lymphatic vessels to the inferior vena cava (F). As the hepatic veins become thicker and more centrally located, the lymphatic vessels form a more intimate network of lymphovascular system.