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
