Introduction Flashcards
What is chemical pathology?
Chemical Pathology (Clinical Biochemistry) – Biochemical investigations of disease, e.g., endocrinology, diabetes, lipidology, thyroid disease inborn errors of metabolism
Which diseases are investigated in haematology?
Diseases of the blood (including leukaemias), blood clotting, blood transfusion and bone marrow transplantation
Which diseases are investigated in immunology?
Diseases of the immune system, e.g., allergy, autoimmunity and immunodeficiency
What does medical microbiology investigate?
Disease-causing microbes including advice on antibiotic usage. They are also responsible for infection control.
What do cellular pathologists do?
– Examine organs, tissues and cells for diagnosis and to guide treatment, often cancer work
– Conduct autopsies
What is cytopathology?
Disaggregated cells rather than tissue
What is neuropathology?
confined to brain, spinal cord, nerves and
muscle
Forensic pathology
medicolegal investigation of suspicious or
criminal deaths, attend crime scenes, perform detailed autopsies
and act as expert witnesses in court
Paediatric pathology
tissue samples from children, undertake
foetal, perinatal and paediatric autopsies
What is the importance of a microscopic diagnosis?
- Definitive diagnosis e.g. Don’t want to remove breast if a lump isn’t cancer
- Before major surgery to remove a lesion a microscopic diagnosis is required
Give an example of a procedure used in histology
Core biopsies, cancer resection specimens, excised skin lesions, endoscopic biopsies
Give an example of a procedure used in cytology
Fine needle aspirates of breast, thyroid, salivary glands, lung; effusions, cervical smears; sputum; urine
Describe the key features of histology
- Often therapeutic as well as diagnostic
- Can assess architecture as well as cellular atypia
- Can differentiate invasive from in situ disease
- Can provide information on completeness of excision and more complete information on grading and staging
- Better for immunohistochemical and molecular testing
Describe the key features of cytology
- Faster and cheaper that histology
- Non-invasive or minimally invasive and safe
- Can be used for cells in fluids
- Sometimes a preliminary test before other investigations or more tissue taken for histology
- Higher inadequate and error rates
- Generally used to confirm/exclude cancer/dysplasia and not to diagnose any other condition
How does a histopathologist arrive at a diagnosis?
• Pattern recognition • This histopathologist asks herself: – Is this normal or not? – Is this inflammatory or neoplastic? – Is this benign or malignant? – Is this a primary tumour or a metastasis?
What can a histopathologist determine about a cancerous sample?
- Type of cancer
- Grade of cancer
- Stage of cancer
- Completeness of excision and if margins are involved which ones
- Likely efficacy of further treatments
How do pathologists use a sample?
Look at the tissue under a microscope
• Take slices from the tissue so thin we can see through
them with a microscope
• Colour the tissue so we can see it under a microscope
What is autolysis?
• Tissue autolysis (self-digestion) begins when the blood supply is cut off
• It destroys cells and tissue architecture
– Everything we need to make a diagnosis
How do you prevent autolysis?
Fixatives:
– Inactivate tissue enzymes and denature proteins
– Prevent bacterial growth
– Harden tissue (to be able to cut cells)
- Usually formalin
Describe the process of fixation
- Hold tissue in ‘suspended animation’
- Use formalin
- Fix for 24-48 hours
How do pathologists chose the right bit of a tissue?
Samples are taken and placed into a cassette
– About the size of a stamp so they can be adequately infiltrated by chemicals
– May need to take 30 or more in complicated cases
– Cassettes have holes in (to allow chemicals in)
– They are placed in racks in formalin
How do pathologists get the tissue hard?
• In order to be able to cut very thin sections the
tissue has to be surrounded and impregnated with a hardening agent
• Usually paraffin wax
• Have to remove the water from the tissue first:
– Dehydration using alcohol in a vacuum so that water is
drawn out of the cells
– Then replace alcohol with xylene which can mix with
wax
– Then replaced xylene with molten paraffin wax, which will even be inside the cells
- Use processors to embed tissue overnight
How to pathologists get the tissue into a piece of wax that can be cut?
- Tissue taken out of the cassettes by hand and put into metal blocks
- These are filled with molten paraffin wax and the body of the cassette is placed on top
- The wax is allowed to harden and the metal tray is removed
How do you cut very thin sections?
Very thin (3-4 microns) sections are cut from the block using a microtome. Sections must be so thin that we can see through them with a microscope
How are wax sections from a microtome put onto microscope slides?
The thin wax sections are floated on a water-bath and picked up on a microscope slide
Which stains are usually used in pathology?
Staining - usually with H&E:
– Haematoxylin stains nuclei purple (From the bloodwood tree)
– Eosin stains cytoplasm and connective tissue pink
– Other stains can be used to demonstrate different substances/structures/micro-organisms
How are tissues preserved and protected/
Mounting:
– Mounting medium is applied to the slide
– Coverslip is put on top
– Mounting medium dries and hardens, preserving the tissue and attaching the coverslip
What is immunohistochemistry?
• Demonstrates substances in/on cells by
labelling them with specific antibodies
• Usually the antibody is joined to an enzyme (e.g., peroxidase) that catalyses a colour-producing reaction
• Highlights the substances usually with a brown colour
What are cytokeratins? How can this be used in pathology?
– Family of intracellular fibrous proteins
– Present in almost all epithelia
- Used frequently in immunohistochemistry
– Markers for epithelial differentiation and show tissue-specific distribution in epithelia (is it epithelial in origin e.g. Carcinoma)
– Can give information about the primary site of a carcinoma, particularly when used in combination:
• CK7+/CK20- : lung, breast, endometrium, ovary, thyroid
• CK7-/CK20+ : large bowel, some gastric carcinomas
What is molecular pathology?
• Studies how diseases are caused by alterations in normal cellular molecular biology
• Can be due to altered DNA, RNA or protein
• In situ molecular tests show how DNA is altered in tissues prepared for microscopy
– E.g., fluorescence in situ hybridisation (FISH) to test for gains of additional copies of Her2 gene in breast cancer
What substances can be tested for using immunohistochemistry?
– Contractile protein actin (identifies smooth muscle cells)
– Cadherins (cell adhesion molecules, deficient in some carcinomas, e.g., lobular breast carcinoma)
– Hormone receptors, e.g., ER, PR – Her2 receptor (growth factor receptor, predicts response of breast cancer to Herceptin)
– Microorganisms, e.g., CMV, HPV, herpes simplex
How do pathologists use DNA sequencing?
• Sequencing of DNA purified from tumour
tissue can show if a mutation is present in a particular gene
– E.g., if certain mutations in EGFR gene are present in lung cancer then the tumour is likely to respond to anti-EGFR treatments, e.g., erlotinib
• Next generation sequencing enables many genes to be tested simultaneously for mutations
What are mRNA expression profile methods used for?
- mRNA expression profiling methods demonstrate the level of activity of a large number of genes simultaneously
- mRNA
What are frozen sections used for?
- Urgent histopathology
- Method of hardening tissue quickly
- Morphology not as good in paraffin sections
- Used mid operation to decide best course of action
- Takes about ten minutes
- Low accuracy
