1. Anatomical Pathology Tissue diagnosis of disease
Tissue taken from patients in the operating theatre, on the ward or from an autopsy
This material is used to make a diagnosis of disease which determines prognosis and guides treatment planning.
Diagnoses not only made on solid tissue samples but also separated cells in form of subspecialty of Cytopathology (FNA, exfoliative cytology, PAP)

2. What is Histopathology?
Histopathology (compound of three Greek words:
'' histos "tissue", πάθος pathos "diseases-suffering", and -λογία'' -logia) refers to the microscopic examination of tissue in order to study the manifestations of disease.

3. Specimen Accessioning
A pathologist is assigned to the case.

4. Autolysis of tissue
Cells contain lysozymes which contain digestive enzymes.
As the cell dies enzymes are released and break down the cells.
Also any bacteria present will break
down the tissues by a process called putrefaction.

5. Fixation - types of fixatives
The purpose of fixation is to preserve tissues permanently in as life-like a state as possible.
Fixation should be carried out as soon as possible after removal of the tissues (in the case of surgical pathology) or soon after death (with autopsy) to prevent autolysis.
There is no perfect fixative, although formaldehyde comes the closest.

6. Fixation - types of fixatives
There are five major groups of fixatives, classified according to mechanism of action:
Aldehydes
Mercurials
Alcohols
Oxidizing agents
Picrates

7. Fixation – Aldehydes (formalin) & Glutaraldehyde
Tissue is fixed by cross-linkages formed in the proteins, particularly between lysine residues.
This cross-linkage does not harm the structure of proteins greatly, so that antigenicity is not lost.
Therefore, formaldehyde is good for immunoperoxidase techniques.

8. Transport media Formalin (histopathology)
Michel’s medium (tissue immunofluorescence)
RPMI (flow cytometry)
Saline or fresh (microbiological evaluation)
Gluteraldehyde (electron microscopy)

9. Gross Examination
Tissues removed from the body for diagnosis are examined by a pathologist.
A macroscopic description is dictated and placing all or parts of the tissue into a small plastic cassette
The cassette will then be processed to a paraffin block.

10. What is the clinical question?
Medical: rashes
Surgical: tumours, vasculitides
Infections: bacterial, fungal, mycobacterial

11. Important clinical information
Patient demographics
Requesting clinician’s information
Clinical history
- duration
- immunocompromised or not
- overseas travel
Clinical morphology (+/- photographs)
Suspected diagnosis or diagnoses

12. Limitations
When the biopsy is performed incorrectly, and without appropriate clinical information, a pathologist's interpretation of a skin biopsy can be severely limited.