Essence of the process and mechanisms of accumulation
Lipidoses are morphological changes characterized by the accumulation of triglycerides and cholesterol esters in the cytoplasm of parenchymatous elements. They are based on three key morphogenetic mechanisms: cell infiltration with excess lipids, decomposition (breakdown of membrane lipoprotein complexes, or phanerosis), and aberrant synthesis. The process most frequently affects the liver, myocardium, and kidneys.
Fatty liver dystrophy (Steatosis)
The liver is affected most frequently due to its central role in triglyceride metabolism. Normally, free fatty acids are converted into lipoproteins in hepatocytes with the participation of apoprotein for export into the bloodstream. When enzymes are blocked, in protein malnutrition, or due to an excessive influx of fatty acids, this mechanism is disrupted.
- Etiology: alcohol intoxication, diabetes mellitus, obesity, hypoxia.
- Macroscopic picture: the organ is enlarged, flabby, yellow, and leaves a fatty residue on the knife («goose liver»).
- Localization: in hyperlipidemia, droplets accumulate at the periphery of the lobule; in hypoxia, in the center.
Myocardial and renal involvement
In the myocardium, fatty dystrophy develops against the background of energy deficit and hypoxia, as well as in diphtheria intoxication due to the blockade of the carnitine shuttle mechanism. Macroscopically, yellow bands are visible beneath the endocardium of the left ventricle («tiger heart»).
In the kidneys, lipids accumulate in the epithelium of the proximal and distal tubules, primarily in nephrotic syndrome due to massive proteinuria and concomitant hyperlipidemia, which leads to lipiduria and increased reabsorption.
Histochemical diagnostic methods
To verify fatty dystrophies, frozen tissue sections are used to prevent lipids from dissolving during processing:
- Sudan III — stains neutral fats orange.
- Sudan IV and scarlet R — impart a red hue.
- Osmium acid and Sudan Black B — stain lipids black.
- Nile blue sulfate — differentiates free fatty acids (dark blue) and neutral fats (red).
Briefly: answers to topical questions
What microscopic types of hepatocyte fatty dystrophy are distinguished depending on the size of lipid droplets?
Depending on the size of lipid inclusions in hepatocytes, three types of dystrophy are distinguished.
- Microvesicular dystrophy — small membrane-bound vacuoles are localized in the cytoplasm, while the cell nucleus is not displaced.
- Medium-vesicular dystrophy — an intermediate variant of lipid accumulation.
- Macrovesicular dystrophy — the extreme expression of the process, in which a huge lipid vacuole displaces the hepatocyte nucleus toward the outer cell membrane (periphery), while the fat-free rim of the cytoplasm remains structurally and functionally intact.
Which diseases belong to hereditary systemic lipidoses (thesaurismoses)?
Hereditary systemic lipidoses (storage diseases, or thesaurismoses) are diseases resulting from a hereditary deficiency of enzymes involved in lipid metabolism.
Main forms:
- Cerebroside lipidosis — Gaucher disease.
- Sphingomyelin lipidosis — Niemann-Pick disease.
- Ganglioside lipidosis — Tay-Sachs disease.
- Generalized ganglioside lipidosis — Norman-Landing disease.
What are the possible outcomes of parenchymatous fatty liver dystrophy?
The possible outcomes of parenchymatous fatty liver dystrophy depend on the form of the disease and the duration of exposure to the etiological factor.
- Reversible outcome: with complete abstinence in alcoholic steatosis, fat disappears from the liver within 2–4 weeks.
- Progression to cirrhosis: prolonged alcohol consumption leads to the development of liver cirrhosis; repeated bouts of acute alcoholic hepatitis play an important role.
- Severe liver dysfunction: characteristic of acute fatty dystrophy, which is a manifestation of massive progressive liver necrosis.
- In chronic fatty dystrophy, liver function may be reduced, but even in severe chronic steatosis, clinical manifestations of dysfunction are rare.
To memorize the staining of fats with Sudan, use the phrase: «Sudan Three is orange inside, Sudan Four is red in the ether».
Class and exam questions
What is phanerosis in parenchymal dystrophies?
Phanerosis is a mechanism of decomposition characterized by the breakdown of masked (bound) lipoprotein complexes within intracellular structures and membranes, leading to the appearance of free neutral fats in the cytoplasm.
What are the main causes of myocardial fatty dystrophy?
The main causes are chronic hypoxia (in anemia and heart failure) and severe intoxications, including diphtheria exotoxin, which blocks the utilization of fatty acids by mitochondria.
Why does fatty liver develop in protein deficiency?
Protein malnutrition disrupts apoprotein synthesis in hepatocytes. Without the transport protein, triglycerides cannot bind into lipoproteins and leave the cell, leading to their accumulation.
What else to study on this topic
- Pathogenesis of alcoholic steatosis and the role of ethanol
- Acute fatty liver degeneration in Amanita phalloides poisoning
- Hereditary systemic lipidoses (Gaucher disease, Niemann-Pick disease)
- Morphological differences of the kidneys in nephrotic syndrome and chronic kidney disease
- The role of polarized light microscopy in lipid research
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