Blood Supply and Systemic Disorders
The liver is distinguished by a unique vascular angioarchitecture characterized by dual blood supply, extremely high intrahepatic blood flow, and a powerful venous outflow system.
Impaired normal blood circulation is recognized as the most common cause of extensive remodeling of liver tissue. An important clinico-morphological feature is that hemodynamic shifts always leave a mark on the organ's structure, but due to high compensatory reserves, the clinical presentation may remain entirely asymptomatic for a long time.
In addition to local problems, the parenchyma suffers from systemic circulatory damage. These most commonly manifest during the development of acute or chronic cardiovascular failure, when adequate global organ perfusion is compromised.
Mechanical Sinusoidal Occlusion
Blockage of the hepatic microvasculature triggers a rapid cascade of pathological reactions.
Main causes of mechanical occlusion:
- Sickle cell anemia.
- Disseminated intravascular coagulation (DIC).
- Hematologic malignancies (lymphomas and leukemias).
Pathogenesis of Injury: The lumen of the sinusoids becomes obstructed by microthrombi or clusters of tumor cells. This causes severe disruption of blood flow and local ischemia. Under hypoxic conditions, hepatocyte necrosis rapidly ensues, ultimately leading to a severe complication: fulminant hepatic failure.
Venous Outflow Pathology
Impaired venous outflow is accompanied by marked macroscopic and microscopic changes and, without timely treatment, carries an extremely high mortality rate.
Macroscopic Appearance: Examination of the vascular bed reveals thrombotic masses in the lumen of the hepatic veins or the inferior vena cava. They can be classified as:
- Fresh occlusive (completely blocking the lumen).
- Mural.
- Organizing (with connective tissue ingrowth).
Histological Changes:
- Severe venous congestion is noted in the central zones of the hepatic lobules.
- Centrilobular hepatocyte necrosis develops.
- If vascular occlusion occurs gradually, fibrosis forms in place of the destroyed cells in the central regions of the lobules.
Veno-Occlusive Disease
This is a specific disorder of the terminal hepatic venules with clear diagnostic criteria and characteristic morphology.
Etiology and Epidemiology: Historically, the disease was first described in Jamaica, where locals drank tea containing toxic pyrrolizidine alkaloids. In modern clinical practice, the primary cause is a specific immune and toxic reaction in bone marrow transplant recipients. In this patient group, the pathology causes death in 30% of cases.
Clinical Presentation: The diagnosis is based on classic symptoms:
- Hepatomegaly with right upper quadrant tenderness.
- Ascites.
- Rapid weight gain (due to fluid retention).
- Jaundice.
Pathomorphology: The core process involves the obliteration of the terminal hepatic venule basin. The mechanism of injury involves marked edema and the deposition of fine-fibrillar collagen in the subendothelial space of the vessels. The cellular infiltrate includes macrophages heavily laden with hemosiderin pigment.
In chronic progression, perivenular fibrosis actively extends deep into the lobular parenchyma. This frequently results in complete obliteration of the central veins and is accompanied by focal tissue hemosiderosis.