Pathology chapters
Pigmentation and pathological calcification
The pigments that build up in tissues from outside (carbon, tattoo ink) and inside the body (lipofuscin, melanin, haemosiderin, bilirubin), and the two types of pathological calcification, dystrophic and metastatic, with their causes and clinical significance.
- Exogenous pigments come from outside (carbon/coal dust in the lungs: anthracosis; tattoo ink); endogenous pigments are made in the body (lipofuscin, melanin, haemosiderin, bilirubin).
- Lipofuscin is the yellow-brown "wear and tear" pigment of ageing; haemosiderin is the iron-storage pigment, stained blue by Prussian blue.
- Dystrophic calcification occurs in dead or damaged tissue with normal serum calcium; metastatic calcification occurs in normal tissue because of hypercalcaemia.
On this page
Overview
Some substances build up in tissues and can be seen as pigments or calcium deposits. Many are harmless markers of past events; others point to disease.
Pigmentation
Exogenous pigments (from outside the body)
| Pigment | Source | Notes |
|---|---|---|
| Carbon (coal dust) | Air pollution, smoking, coal mining | The commonest exogenous pigment; taken up by alveolar macrophages and carried to hilar lymph nodes. Anthracosis blackens lungs and nodes; heavy exposure in miners causes coal workers' pneumoconiosis |
| Tattoo ink | Injected into the dermis | Taken up by macrophages in the dermis; permanent; usually harmless |
| Others | Lead (gum line), silver, gold | Rare |
Endogenous pigments (made in the body)
| Pigment | Colour | Features |
|---|---|---|
| Lipofuscin | Yellow-brown, granular | "Wear and tear" or ageing pigment; undigested remains of lipid peroxidation in lysosomes. Seen in the heart, liver and brain of the elderly and in atrophy (brown atrophy). A sign of past free-radical injury, harmless in itself |
| Melanin | Brown-black | Made from tyrosine by tyrosinase in melanocytes; protects against UV. Increased in Addison's disease, pregnancy (melasma); absent in albinism and vitiligo |
| Haemosiderin | Golden-brown granules | Iron storage pigment (ferritin aggregates). Stained blue by Prussian blue (Perls) stain |
| Bilirubin | Yellow-green | From haem breakdown; excess causes jaundice |
| Homogentisic acid | Black | In alkaptonuria (ochronosis of cartilage) |
Lipofuscin = wear and tear (ageing) pigment. Haemosiderin = iron, Prussian blue positive.
#### Haemosiderin in detail
- Local: a bruise: red cells break down; haemoglobin turns to biliverdin (green), bilirubin (yellow) and haemosiderin (golden-brown), which explains the changing colours of a bruise.
- Systemic haemosiderosis: iron overload from repeated blood transfusions (thalassaemia major), haemolysis or excess iron intake; iron deposits in macrophages and organs.
- Haemochromatosis: an inherited disorder (HFE gene) of increased iron absorption; iron damages the liver (cirrhosis), pancreas (diabetes), heart and skin (bronze colour): "bronze diabetes".
Patients with thalassaemia major in Pakistan develop transfusion-related iron overload and need iron chelation.
Pathological calcification
Abnormal deposition of calcium salts (mainly calcium phosphate) in tissues. On H&E it looks purple-blue and granular; special stains are von Kossa and alizarin red.
Dystrophic calcification
- Occurs in dead or degenerating tissue.
- Serum calcium is normal.
- The commonest type.
Examples:
- Atheromatous plaques in arteries.
- Damaged or aged heart valves (calcific aortic stenosis).
- Caseous necrosis in old tuberculosis (calcified lymph nodes, Ghon complex).
- Fat necrosis (pancreas, breast).
- Dead parasites (hydatid cyst wall), thrombi (phleboliths in veins).
- Tumours, as psammoma bodies.
Psammoma bodies: concentric, laminated calcified spheres, seen in papillary thyroid carcinoma, serous papillary tumours of the ovary, meningioma and mesothelioma.
Dystrophic = dead tissue, normal calcium. Psammoma bodies: papillary thyroid carcinoma, serous ovarian tumours, meningioma.
Metastatic calcification
- Occurs in normal tissues.
- Caused by hypercalcaemia (or high phosphate).
- Favours tissues that lose acid and so have an alkaline internal environment: lungs (alveolar walls), kidneys (nephrocalcinosis), stomach (gastric mucosa), blood vessels and the cornea.
Causes of hypercalcaemia:
- Hyperparathyroidism (primary or secondary).
- Chronic kidney disease (high phosphate, secondary hyperparathyroidism).
- Bone destruction: metastatic cancer, multiple myeloma, Paget's disease, immobilisation.
- Vitamin D excess, sarcoidosis.
- Milk-alkali syndrome.
| Feature | Dystrophic | Metastatic |
|---|---|---|
| Tissue | Dead or damaged | Normal |
| Serum calcium | Normal | High |
| Examples | Atheroma, damaged valves, old TB, fat necrosis, psammoma bodies | Hyperparathyroidism, renal failure, vitamin D excess, myeloma |
| Common sites | Wherever there is necrosis | Lungs, kidneys, stomach, vessels |
Clinical significance
- Calcified valves cause aortic stenosis.
- Calcified coronary arteries indicate atherosclerosis (coronary calcium score).
- Nephrocalcinosis impairs kidney function.
- Calcification helps diagnosis on imaging: calcified TB foci, breast microcalcifications on mammography (can indicate cancer), calcified masses.
Expect: exogenous vs endogenous pigments with examples, lipofuscin as the ageing pigment, the Prussian blue stain for haemosiderin, bruise colour changes, haemosiderosis vs haemochromatosis, dystrophic vs metastatic calcification (tissue and serum calcium), sites of metastatic calcification, and tumours with psammoma bodies.
Quick revision
- Exogenous: carbon (anthracosis), tattoo.
- Endogenous: lipofuscin (ageing), melanin, haemosiderin (Prussian blue), bilirubin.
- Haemochromatosis: liver, pancreas, heart, skin ("bronze diabetes").
- Dystrophic: dead tissue, normal calcium (atheroma, valves, TB).
- Metastatic: normal tissue, high calcium (hyperparathyroidism, renal failure, vitamin D).
- Psammoma bodies: papillary thyroid, serous ovarian, meningioma.
Written by The House Job from standard pathology references (Robbins and Cotran Pathologic Basis of Disease is the book named in the UHS PGET syllabus).
FAQ
What is lipofuscin?
A yellow-brown "wear and tear" pigment that builds up in cells with ageing and atrophy.
Which stain identifies haemosiderin?
The Prussian blue (Perls) stain.
What is the difference between dystrophic and metastatic calcification?
Dystrophic calcification occurs in dead or damaged tissue with normal serum calcium; metastatic calcification occurs in normal tissue because of hypercalcaemia.
Which tumours contain psammoma bodies?
Papillary thyroid carcinoma, serous ovarian tumours and meningioma, among others.