Histopathology Flashcards
Define histopathology.
The study of changes in tissue associated with disease.
Define Cytopathology
The study of changes in cells associated with disease.
What are the purpose of histopathological samples being taken?
- Screening programmes highlight some abnormalities.
- To aid diagnostic processes.
- To aid therapeutic processes.
- To determine prognosis and direct treatment.
When is bowl cancer screening needed?
If there is blood in the faces.
When is cervical screening carried out?
If the HPV virus is detected.
What are the guidelines for screening programmes?
Benefits should outweigh negatives, target population should be large.
What is the aim of histology?
To generate a microscope slide for a pathologist to make a diagnosis from.
What are the steps to produce a histological sample?
- Receipt/ booking in
- Fixation
- Dissection
- Processing
- Embedding
- Microtomy
- Staining
- Special Stains
- Immunohistochemistry
Where do histopathological samples come from?
GPs surgeries, outpatient clinics or from surgery.
Describe the labelling on histopathological samples.
At least 3 forms of labelling are critical to ensure the sample and its identity correspond.
What substance are most histological samples fixed in and what is this?
Formalin - a pungent gas soluble in water.
Why may formalin not be used in the fixation process of pathology?
Formalin impedes some studies of proteins by cross-linking with them. So it is often not used if specific protein structure and function needs to be maintained.
What is the aim of the dissection process of histopathology?
To transfer pieces of tissue onto cassettes.
What does the technique used in dissection depend on?
Sample size
Describe dissection of small samples
Does not require any dissection or sampling.
Describe dissection of intermediate specimens
Require dissection and sampling, some may have representative pieces taken.
Describe dissection of large specimens.
Dissection by consultant pathologists.
What is the aim of the processing part of the histological process ?
To remove water from the tissue and infiltrate with molten paraffin wax.
What are the reagents for processing in histopathology?
Alcohol
xylene
Molten wax
What is the aim of embedding in histopathology.
To transfer the tissue into a wax block.
What factor is important in the embedding process in histopathology?
Sample orientation
What is the aim of microtomy in the histological process?
To shave a thin section of tissue from the wax block and mount onto a microscope slide so it can be stained.
What piece of equipment is used in microtomy?
A microtome
How thick should samples be after microtomy?
3-4 microns thick typically
What dyes are typically used for staining in histopathology?
H&E
Describe how H&E staining works.
Haematoxylin is a basic due which stains acidic structure such as DNA in the cell nucleus (stains blue)
Eosin is an acidic dye which stains basic structures pink
What does is immunohistochemistry used to stain?
Antigens in tissue
What is immunohistochemistry useful for ?
Determining what specific type of cancer a person may have.
Outline what happens in immunohistochemistry.
Histological, immunological and biochemical techniques are combined for the identification of specific tissue components by means of specific antibody/antigen reaction tagged with. a visible label. It involves the process of selectively identifying antigens in cells of a biological specimen by exploiting the principle of antibodies binding specifically to antigens in biological tissues.
Why is formalin used for fixation?
- It preserves tissue in a ‘life like state’.
- Prevents cell autolysis.
- Kills bacteria and viruses
- It forms cross links with proteins and preserves them.
What virus does formalin not kill?
CJD
What issues can occur during fixation?
Fixation can introduce artefacts (any structure or feature in the histological section, which is not normally present in the normal tissue, and it may come from outside sources).
What are the possible mechanical transmission methods of prion disease?
Acquired, sporadic and familial
What symptoms can occur due to prion diseases?
o Myoclonus, ataxia
o Often presents with personality change
o Gait rapidly affected
o Aphasic, no eye contact, no memory
What methods are used to diagnose prion diseases?
MRI
EEG
CSF analysis
What is good about immunohistochemistry?
- Antibodies bind to antigen in specific manner
- Can be used to locate particular cells and proteins where protein expression varies in space
- Can be used to identify cellular events such as apoptosis where protein expression varies over time
- It is possible to visualise multiple targets simultaneously using immunohistochemistry.
In histochemistry, immunoglobulins will ‘stick’ specifically to the antigens against which they are raised in the fixed tissues/ cells. But how do we see them?
Add something that permits visualisation – enzyme, fluorophore etc. But why modify every antibody you make when you can create a generic ‘secondary antibody’ directed at the unchanging part of the ‘primary’ antibody.
Describe direct immunohistochemsitry.
- Primary antibody only
o A cell with an antigen attached to it. The antibody binds to this which is conjugated to a fluorescent marker and allows detection.
Describe indirect immunohistochemistry.
- Uses primary and secondary antibodies
o Primary antibody binds to antigen on cell surface. Fluorescently labelled secondary antibody then binds to primary antibody. - This allows more specific detection
- Allows amplification of signal
What are the benefits of indirect immunohistochemsitry ?
Allows more specific detection and signal amplification.
Describe how colposcopy works.
- Uses Acetic acid:
o Abnormal areas appear white due to higher DNA content
o Normal areas do not stain - Uses Lugol’s Iodine:
o Normal cells appear brown due to high glycogen content
o Abnormal cells wont stain
What is colposcopy ?
An examination of the cervix that is carried out if there are any concerns of HPV or cervical cancer.
Describe the treatment of HPV.
- Remove the area of concern with a clear margin around it. This will hopefully be curative and prevent the development of cervical cancer.
- This is done outpatient in colposcopy
Describe the structure of the lobes and ducts of a healthy breast.
- Lobes and ducts form a tree like structure where the ducts are like the branches of trees and the lobules are the leaves.
- A lobule has multiple acini.
Healthy histology - 2 layers of epithelial tissue
- Myoepithelial – contractile ( help excrete milk)
- Luminal – secretory
What are the different possible causes of breast lumps?
- Lipoma
- Fibroadenoma
- Carcinoma
- Phyllodes tumours
- Cyst
- Fat necrosis
What is a lipoma?
Bening proliferation of adipose tissue.
What is a fibroadenoma?
Benign tumour with epithelial and stroll involvement.
In what people are fibroadenomas common?
Women in their 20s and 30s.
In what people are carcinomas common?
Patients 60+ or with a genetic mutation
Describe the histopathology of carcinoma.
Loss of myoepitheial layer
Describe the immunohistochemsitry of carcinoma.
The antibody p63 positively stains the myoepithelial layer
There is no p63 staining in breast carcinoma because the myoepithelial layer has been lost
