Pathologic accumulations refer to abnormal buildup of substances within cells or tissues. These may be normal substances in excess or abnormal materials due to metabolic or genetic defects.
Types of Intracellular Accumulations
- Lipids: Excess lipid synthesis or defective metabolism
- Triglycerides → fatty liver
- Cholesterol → atherosclerosis, xanthomas
- Complex lipids → sphingolipidosis (e.g., Gaucher disease)
- Proteins: Excess protein load or misfolding
- Reabsorption droplets in renal tubular cells (proteinuria)
- Russell bodies in plasma cells (multiple myeloma)
- Glycogen: Enzyme defects in glycogen metabolism → accumulation → cell death.
- Glycogen storage diseases (e.g., von Gierke, Pompe)
- Hyaline: Non-specific, “glassy pink” on H&E stain due to protein accumulation.
- Hyaline arteriolosclerosis
- Amyloid deposits
- Hyaline membrane disease (newborns)
Pathologic Calcifications
| Type | Definition | Sites / Examples | Mechanism |
|---|---|---|---|
| Dystrophic Calcification | Deposition of calcium salts in damaged or necrotic tissues | – Fat necrosis (pancreas) – Atherosclerotic plaques – Psammoma bodies (meningioma, papillary thyroid CA) |
Normal serum calcium; local tissue injury acts as a nidus for deposition |
| Metastatic Calcification | Deposition of calcium salts in normal tissues due to hypercalcemia | – Kidneys, lungs, stomach, vessels | ↑ Serum calcium (e.g., hyperparathyroidism, renal failure, vitamin D intoxication, sarcoidosis, Paget disease, multiple myeloma, malignancy) |
Pigment Accumulations
1. Exogenous Pigments
| Pigment | Source / Example | Clinical Note |
|---|---|---|
| Anthracosis | Inhaled carbon dust | Black lung pigment in smokers or coal workers |
| Tattoo pigments | Injected exogenous ink | Stored in dermal macrophages |
| Lead | Environmental or occupational exposure | Gingival lead line, renal tubular inclusions |
2. Endogenous Pigments
| Pigment | Description | Pathologic Feature / Example |
|---|---|---|
| Lipofuscin | “Wear-and-tear” pigment (yellow-brown, perinuclear) | Aging, malnutrition, and chronic disease, found in the liver and heart |
| Melanin | Black-brown pigment from tyrosine | Found in melanocytes, the substantia nigra |
| Hemosiderin | Golden-brown granular pigment (iron storage) | Found in areas of hemorrhage, bruises |
| Bilirubin | Yellow-green bile pigment | Excess causes jaundice or kernicterus in newborns |
| Iron overload states | – Hemosiderosis → excess iron without tissue injury – Hemochromatosis → excess iron with tissue injury |
Detected by Prussian blue stain |
Key Points to Remember
- Dystrophic calcification = dead tissue + normal calcium level.
- Metastatic calcification = normal tissue + elevated calcium level.
- Lipofuscin → marker of oxidative stress and aging.
- Russell bodies = protein accumulation in plasma cells.
- Prussian blue stain identifies iron in hemosiderin.
- Hyaline = “glassy pink” appearance on H&E stain, not a specific substance.
Learning Objective
By the end of this topic, the student should be able to:
- Identify major types of intracellular and extracellular accumulations.
- Differentiate between dystrophic and metastatic calcification.
- Recognize key pigments (exogenous and endogenous) and their pathologic significance.
- Correlate cellular accumulations with underlying disease mechanisms.
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