Introduction
Vascular Obstruction in Chronic Liver Disease
The Parenchymal Extinction Sequence
Laennec stage | The parenchymal extinction sequence (PES) | |
---|---|---|
Stage (description) | Level | Definition (comment) |
0–1 (septa−) | 1 | Stress zones with variegation of the color of hepatocyte cytoplasm in clusters the size of lobular units. |
0–1/septa−) | 2 | Stress zones with hepatocellular atrophy. |
3 | open-PELs - Small region of hepatocellular dropout - necrosis or apoptosis- without collapse (represents necrosis, if recent, or a pressurized common channel (PCC) if chronic, occurring after lysis of a number of adjacent sinusoidal walls) | |
1 (septa−, with portal expansion) | 4 | closed-PELs - Small region of hepatocellular dropout with collapsed architecture and approximation of portal tracts and hepatic veins. (Lesions are usually detectable with glutamine synthetase stain.) |
2 | 5 | Merged PELs that form small aggregates or short septa containing 2–3 PTs. (These aggregated PELs may also be open or closed.) |
3–4A (septa++) | 6 | Extended PEL aggregates that form a network of septa (thin septa if closed). |
4B–4C (septa+++) | 7 | Large PEL aggregates containing many portal tracts crowded together, with each PT surrounded by collapsed stroma rather than hepatocyte plates |
Regressing cirrhosis (septa PES level 8) | 8 | Septa are thin links between remnants of portal tracts and hepatic veins (found in early regression of septa/cirrhosis) |
Regressing cirrhosis (septa PES level 9) | 9 | Former septa that are fragmented, leaving collagenous tags attached to recognizable PT remnants or HV remnants but not definitely connected to a septum (found in late regression of septa/cirrhosis. Some of these tags may be residual strings of PT stroma or linear remnants of HVs walls.) |
Congestive Vasculopathy and the Congestive Escalator
Discussion
Role of Endothelial Cell Injury
Conclusion
- Cirrhosis is the morphologic result of parenchymal extinction that leads to collapse of tissue to form septa. Parenchymal extinction is characterized by focal loss of hepatocytes as well as destruction of sinusoids and obstruction of small portal and hepatic veins.
- Parenchymal extinction is initiated by a primary liver disease that causes vascular injury, usually at the level of sinusoidal endothelial cells. Sinusoidal injury progresses to parenchymal extinction by a sequence of events that involve vascular leak, transudation into vein walls and interstitium, ischemia, and hyperemia. The resultant microvascular obstruction causes further congestive injury and the extension of venous obstruction to larger vessels in a positive feedback loop called the “congestive escalator,”
- The human liver is particularly vulnerable to this congestive escalator because the “nested cone” architecture, mandated by the long and branched hepatic vein tree, is susceptible to “compartment syndrome” effects. Animals used for most experimental models have a very short hepatic venous tree that is unlikely to produce the prominent congestive effects found in human liver disease. This difference suggests that the pathogenesis of cirrhosis in humans and animal models may be quite different.