Pathology
Staining
To give an example of the process of preparing a tissue for histopathological examination let's consider the preparation of brain slices.
Brain is fixed in 10% formalin and then cut into chunks and embedded in paraffin. Paraffin embedded brain can then be sectioned into thin slices, stretched in a water bath and then mounted on slides ready for staining.
Some of the most commonly used stains are detailed below.
| Stain | Description |
|---|---|
| Haematoxylin and Eosin | Haematoxylin is a basic dye which stains the nucleus blue. Eosin is an acid dye that statins cytoplasm pink. |
| Elastika van Gieson | |
| Prussian blue | Stains haemosidderin providing a lifelong indicator of prior bleeding. |
| Nissl stain |
A number of different artefacts can occur: - Variations in slice thickness can produce the impression of hyper or hypo cellularity - V-cleft - Wringles - Scratches - Bubbles - Formalin precipitants
The image below shows how the appearance of white matter within the brain varies with slice thickness.
In addition to these artefacts, the process of obtaining tissue can result in haemorrhage. This haemorrhage is acute and is usually readily identified by the presence of erythrocytes outside a blood vessel in the absence of a tissue reaction.