Published online Jul 21, 2020. doi: 10.3748/wjg.v26.i27.3899
Peer-review started: February 27, 2020
First decision: April 30, 2020
Revised: May 12, 2020
Accepted: June 23, 2020
Article in press: June 23, 2020
Published online: July 21, 2020
Processing time: 144 Days and 22.4 Hours
The phenomenon of liver regeneration after partial hepatectomy (PH) is still a subject of considerable interest due to the increasing frequency of half liver transplantation on the one hand, and on the other hand, new surgical approaches which allow removal of massive space-occupying hepatic tumors, which earlier was considered as inoperable. Interestingly, the mechanisms of liver regeneration are extensively studied after PH but less attention is paid to the architectonics of the regenerated organ. Because of this, the question “How does the structure of regenerated liver differ from normal, regular liver?” has not been fully answered yet. Furthermore, almost without any attention is left the liver's structural transformation after repeated hepatectomy (of the re-regenereted liver).
To compare the architectonics of the lobules and circulatory bed of normal, re-generated and re-regenerated livers.
The livers of 40 adult, male, albino Wistar rats were studied. 14 rats were subjected to PH - the 1st study group (SG1); 10 rats underwent repeated PH – the 2nd study group (SG2); 16 rats were subjected to sham operation - control group (CG); The livers were studied after 9 months from PH, and after 6 months from repeated PH. Cytological (Schiff reaction for the determination of DNA concen-tration), histological (H&E, Masson trichrome, CK8 Immunohistochemical marker, transparent slides after Indian Ink injection, ), morphometrical (hepatocytes areas, perimeters and ploidy) and Electron Microscopical (Scanning Electron Microscopy of corrosion casts) methods were used.
In the SG1 and SG2, the area of hepatocytes and their perimeter are increased compared to the CG (P < 0.05). However, the areas and perimeters of the hepatocytes of the SG1 and SG2 groups reveal a lesser difference. In regenerated (SG1) and re-regenerated (SG2) livers, the hepatocytes form the remodeled lobules, which size (300-1200 µm) exceeds the sizes of the lobules from CG (300-600 µm). The remodeled lobules (especially the “mega-lobules” with the sizes 1000-1200 µm) contain the transformed meshworks of the sinusoids, the part of which is dilated asymmetrically. This meshwork might have originated from the several portal venules (interlobular and/or inlet). The boundaries between the adjacent lobules (including mega-lobules) are widened and filled by connective tissue fibers, which gives the liver parenchyma a nodular look. In SG2 the unevenness of sinusoid diameters, as well as the boundaries between the lobules (including the mega-lobules) are more vividly expressed in comparison with SG1. The liver tissue of both SG1 and SG2 is featured by the slightly expressed ductular reaction.
Regenerated and re-regenerated livers in comparison with normal liver contain hypertrophied hepatocytes with increased ploidy which together with transformed sinusoidal and biliary meshworks form the remodeled lobulli.
Core tip: Liver regeneration after partial hepatectomy (PH) is based on both proliferation and hypertrophy of hepatocytes. These cells unite into remodeled lobules, the sizes of which vary widely. The microcirculation of the liver is also re-modeled. At the same time, there is a suspicion that hyperplasia-hypertrophy and remodeling do not apply to all hepatocytes and all lobules; it is also possible that, in parallel with remodeling, new lobules are formed. After repeated PH, liver regeneration is based on the same type of transformations, although their intensity is less. To fully evaluate the lobular and microcirculatory architecture of regenerated liver after both, PH and repeated PH, it is necessary to investigate the architectonics of the initials of the biliary system.