Intro to Pathology

Question 1

What is disease?

Answer 1

A pathological condition of a body part, organ or system characterised by an identifiable group of signs or symptoms.

• Failed homeostasis with consequent morphological and function disturbances

Question 2

What is pathology?

Answer 2

Study of suffering: involves diagnosis and explanations of why patients experience certain symptoms

Question 3

Why are microscopic diagnoses important?

Answer 3

• Provide a definitive diagnosis
• Done before a major surgery to remove a lesion
• Guides type and extent

Question 4

What are features of histology?

Answer 4

Resections, excisions, core biopsies

• Therapeutic and diagnostic
• Differentiation of invasive from in situ
• Better for immunohistochemical and molecular testing

Question 5

What are features of cytology?

Answer 5

Smears, sputum, fine needle aspirates

• Faster and cheaper
• Non-invasive
• Can be used to confirm/exclude cancer or dysplasia
• Higher inadequate and error rates

Question 6

How is a diagnosis made?**

Answer 6

Pattern recognition

• Normal/abnormal?
• Inflammatory/neoplastic?
• Benign/malignant?
• Primary/metastases?

Question 7

What can histopathology tell with regards to cancer?

Answer 7

• Type of cancer
• Grade of cancer
• Stage of cancer
• Completeness of excision
• Likely efficacy of further treatment

Question 8

What is used to determine the stage of cancer?*

Answer 8

TNM

• T: tumour size
• N: nodes - whether it invaded just local nodes or distant nodes too
• M: metastases - only in the tissue of origin or spread to other?

Question 9

What is a problem with analysing tissues?

Answer 9

Tissue autolysis - self digestion when the blood supply is cut off that destroys cell and tissue architecture

Question 10

How is autolysis prevented?

Answer 10

By using fixatives (formaldehyde) that inactivates enzymes needed for autolysis, prevent bacterial growth and harden tissue
- Will fix tissue for 24-48 hours

Question 11

How is the tissue hardened so that thin slices can be made?

Answer 11

• Use paraffin wax
• Dehydrate tissue first using alcohol in a vacuum so that water is drawn out of cells
• Replace alcohol with xylene
• Replace xylene with molten paraffin wax

Question 12

How are thin sections of tissue cut?

Answer 12

• Using a microtome
• Must be thin enough to be able to see through them with a microscope
• Thin wax sections floated on a water bath and picked up on a microscope slide

Question 13

How is tissue stained?

Answer 13

Usually H&E

• Haematoxylin: nuclei stained purple
• Eosin: cytoplasm and connective tissue stained pink

Question 14

How is the tissue preserved and protected?

Answer 14

• Mounting medium applied to slide
• Coverslip on top
• Mounting medium dries and hardens to preserve tissue and attach coverslip

Question 15

What is immunohistochemistry?

Answer 15

• Labelling substances with specific antibodies
• Antibody joined to an enzyme that catalyses a colour-producing reaction (peroxidase)
• Stains brown

Question 16

What can be identified?

Answer 16

• Smooth muscle cells (contractile protein actin)
• Cadherins
• Hormone receptors (eg. oestrogen)
• HER2 receptor (predicts response of breast cancer to herceptin)
• Microorganisms

Question 17

What are cytokeratins and what are they used for?

Answer 17

• Family of intracellular fibrous proteins present in almost all epithelia
• Show tissue specific distribution in epithelia
• Can give information about the primary site of a carcinoma

Question 18

What is molecular pathology?

Answer 18

Sequencing of DNA purified from tumour tissue that can show if a mutation is present in a particular gene and therefore what treatment it might respond to

Question 19

What are frozen sections used for?

Answer 19

• Urgent histopathology
• Mostly intra-operative: establishes presence and nature of a lesion and influences the course of the operation
• Takes about 10 minutes from receiving specimen to giving result
• 96% accuracy