Day 1- Lecture 1- Introduction To Pathology Flashcards
Name the 5 different branches of pathology and outline what they study?
Medical microbiology (including virology)- study of infectious disease
Chemical pathology- study of disturbances in metabolic processes
Haematology- study of blood disorders
Immunology- study of diseases of the immune system
Cellular pathology- includes:
- Histopathology which uses macroscopic and microscopic assessment of tissue samples
- Cytopathology which looks at macroscopic and microscopic assessment of disaggregated cell samples
Give a brief outline of the job roles in medical microbiology, chemical pathology, haematology, immunology and cellular pathology
Microbiology: working in labs, offer advice on antibiotic use age, offer advice to clinical areas e.g. ITU, haematology, paediatrics
Chemical pathology: oversee labs, offer clinical services in diabetes, thyroid disease, endocrinology and lipidology
Haematology: bone marrow transplant, blood transfusions, coagulation, haemato-oncology, haemoglobinopathy
Immunology: labs and work with patients who have a variety of disorders leading to allergy, autoimmunity and immunodeficiency
Cellular pathology:
- Neuropathy- brain, spinal cord, nerves, muscle
- Forensic pathology- attend crime scenes and perform autopsies for suspicious deaths
- Paediatric pathology- look at histropathological specimen from children and deal with perinatal, foetal and paediatric autopsies
What is the difference between histology and cytology?
Histology- microscopic slides prepared from tissues sections- used both diagnostically and therapeutically when a lesion is removed
Cytology- study cells scraped/sucked out of an organ/lesion OR extracted from a bodily fluid e.g. Urine or pleural effusion
What are the advantages and disadvantages of using histology vs cytology?
Cytology- Advantages: -Non/minimally invasive -Cheap -Fast -Generally safe -Can be used for cells in fluids Disadvantages: -Higher inadequate/error rates
Histology-
Advantages:
-Architecture as well as cell atypia are assessed
-Can differentiate between in situ and invasive malignancy/disease
-It allows comment on completeness of excision
-Can grade and stage cancers
-Often therapeutic and diagnostic
-Better for immunohistochemical molecular testing
Disadvantages of both histo and cytopathology:
- Sometimes mis-diagnosis of low grade atypias and malignancies
- Sometimes histological interpretation is SUBJECTIVE
Cytology: sometimes used as a preliminary before other investigations or before more tissue is taken, and it is generally used to confirm/exclude cancer or dysplasia not to diagnose any other condition with accuracy
Is a histopathologist diagnoses a cancer what further information can they find which will influence the future management and treatment of the patient?
Type of cancer
Grade of cancer
Stage of cancer
Likely efficacy of treatments
Why is examination of tissues important and what information is obtained from such information?
Before any major surgical removal, a microscope diagnosis is needed to ensure the surgery is required and to guide the type and extent of surgery-
Sometimes a microscopic diagnosis:
-Reassures that the lesion can be left alone
-Indicates that the patient requires treatment other than surgery e.g. Chemotherapy, antibiotics, steroid or even palliative treatment
Give some examples of when histology and cytology are used?
Histology: core biopsy, cancer resection specimens, excised skin lesions, endoscopic biopsies
Cytology: fine needle aspirates of breast, thyroid, salivary glands, lung, effusions, cervical smears, sputum, urine
Outline the process for preparing a specimen for microscopy-
AUTOLYSIS + FIXATION:
-Blood supply is cut off- destroys cells and tissue architecture. Blocks the biochemical process of autolysis with fixatives-
Fixatives:
-Inactivate tissue enzymes and denature proteins
-Prevent bacterial growth
-Harden the tissue so that a thin section can be cut
Process of Fixation:
-Hold the tissue in suspended animation
-Usually use formalin (formaldehyde and water)
-Penetrates the tissue at approx 1mm/hour
-Usually fixes the tissue for 24 to 48 hours
CUT UP/TRIMMING
- Pathologist takes sample and places in cassette
- Sample is small so can be adequately filtrate by chemicals
- Complicated cases- may have to take over 30 samples
- Cassettes have holes in and places in racks of formalin
EMBEDDING (PROCESSING)- getting the tissue hard enough to take very thin slices
-Use paraffin wax (a hardening agent that surround tissue so that it can be cut thinly)
Have to remove water from tissue first:
-Use alcohol in a vacuum to dehydrate the cells and cause water to drain out of the cells
-Replace alcohol with xylene which can mix with wax
-Replace xylene with molten paraffin wax which will be outside and inside the cells
BLOCKING- getting tissue into piece of wax that can be cut out
- Tissue taken out of cassettes by hand and put into metal blocks
- Filled with molten paraffin and the body of the cassette is placed on top
- Wax is allowed to harden and metal tray is removed
MICROTOMY- cutting very thin sections
- Very thin sections are cut from the block using a microtome -> so thin that we can see through with microscope
- Thin wax sections float on water bath- picked up by a microscope slide
STAINING- colour tissue so it can be seen under the microscope
Stain using H&E
-Haematoxylin- stain nuclei purple
-Eosin- stains cytoplasm and connective tissue pink
Other substances can be used to demonstrated different substances/structures/microorganisms
MOUNTING- preserving and protecting the slice of tissue
- Mounting medium is applied to the slide
- Coverslip is out on top
- Mounting medium dries and hardens, preserves tissue and attaches coverslip
MICROSCOPE- makes diagnosis
REPORT WRITING
What two other methods can be used if viewing stained slides does not provide all the information?
Immunohistochemistry and molecular pathology
Describe and give examples of immunohistochemistry-
- Demonstrates the presence in or on cells of specific substances
- Usually antibodies are joined to an enzyme (e.g. Peroxidase) that catalyses a colour producing reaction- common colour is brown
Any antigenic substance can be demonstrated:
- Contractile protein actin- identifies smooth muscle cells
- Microorganisms
- Hormone receptors e.g. Oestrogen and progesterone receptors
- Her2 receptor- a growth factor receptor which predicts the response of breast cancer to the drug herceptin
- Cytokeratins- a family of fibrous proteins present in almost all epithelial cells, markers for epithelial differentiation and shows a tissue specific distribution in epithelia, can give information about the primary site of a carcinoma.
Describe and give examples of molecular pathology?
Study of diseases are caused by alterations in normal cellular molecular biology- could be due to alterations in DNA, RNA or protein
Molecular tests that show how DNA is altered in the context of microscopic tissue structure:
- FISH (Fluorescent In Situ Hybridisation)- tests for gains of additional copies of genes e.g. HER2 in breast cancer to show if a particular tumour is likely to respond to anti-HER2 treatments like Herceptin. FISH can also show if genes have been translocated (i.e. Broken and/or rearranged) or completely detected from the genome.
- Sequencing of DNA purified from tumour tissue can show if a mutations is present in a particular gene (i.e. Single nucleotide change)
- Next generation sequencing enables many genes to be tested simultaneously for mutations
- mRNA expression profiling methods can show how active a large number of genes are at the RNA level- useful diagnostically as mRNA expression ‘signatures’ can predict how a given tumour is likely to behave e.g. The risk of cancer spread/reoccurrence after surgery for breast cancer
Outline what should be included in a histology report?
- Clinical history
- Macroscopic
- Microscopic
- Conclusion
Why are frozen sections used and how is it carried out?
Usually during the course of an operation under tight time constraints- bypasses the process of formalin fixation and embedding paraffin wax
INSTEAD…
-Rapidly freeze small piece of fresh tissue on a cryostat (hardens the tissue quickly)
-Get fresh piece of tissue/specimen, put the bit of tumour in a cryostat which rapidly freezes the tissues, slice it thinly with microtome, stained, mounted and passed to pathologist for microscopy (takes around 10 minutes from receipt of tissue in lab to provision of result to clinician)
AIM of frozen section:
Establish the presence and nature of lesion and influence the course of the operation - for example - determine whether a tumour in the lung is a cancer or inflammatory mass and hence whether the love of lung should be respected or not
What are the disadvantages of frozen sections?
Morphology is not as good- harder to interpret so it ca have errors/false negatives
