Microscopic study of the normal tissues of the body
Histopathology
Microscopic study of tissues affected by disease
Histologic/histopathological techniques
Procedures adopted for the preparation of material for histology and histopathology studies
Obtaining tissue samples
1. Surgery
2. Biopsy
3. Autopsy
Fine needle aspiration
Simplest, least invasive test
Uses smallest needle to remove cells from area of abnormality
Not always adequate to obtain diagnosis
Core needle biopsy
Removes cells and small amount of surrounding tissue
Provides additional information to assist in examination of lesion
Incisional biopsy
Takes out more surrounding tissue
Takes out some of the abnormality, but not all
Further surgery may be needed if lesion is cancerous
Excisional biopsy
Generally removes the entire area in question
Punch biopsy
Primary technique for obtaining diagnostic full-thickness skin specimens
Requires basic surgical and suture-tying skills
Yields a 3-4 mm cylindrical core of tissue sample
Shave biopsy
Small fragments of tissue are "shaved" from a surface (usually skin)
Curettings
Tissue is scooped or spooned to remove tissue or growths from body cavity
Autolysis
Self-digestion of tissues after death
Teasing or dissociation
Tissue specimen is immersed in isotonic salt solution, carefully dissected with a needle, separated by direct or zigzag spread using an applicator stick
Squash preparation (crushing)
Small pieces of tissue are placed on a slide and forcibly compressed with another slide or cover glass
Streaking
1. Small pieces of tissue are placed on a slide and forcibly compressed with another slide or cover glass
2. Too thin or too thick smears have to be avoided
Spreading
Selected portion of material is transferred to a slide and gently spread into moderately thick film by teasing mucous strands apart with an applicator stick
Pull-apart
Drop of secretion/sediment is placed on one slide over another slide, slides are pulled apart with a single uninterrupted motion
Frozen section
1. Fresh tissue is frozen on a microtome with CO2 or cryostat
2. Thin frozen sections are mounted on a slide, fixed, and stained
Frozen sections
Used for rapid pathologic diagnosis during surgery
Diagnostic and research enzyme histochemistry
Demonstration of soluble substances like lipids and carbohydrates
Immunofluorescent and immunohistochemical staining
Some specialized silver stains
Freezing methods
1. Liquid nitrogen
2. Carbon dioxide gas
3. Isopentane cooled by liquid nitrogen
4. Aerosol sprays
Cold knife procedure
Tissue blocks can be frozen by adapting a conventional freezing microtome gas supply of carbon dioxide gas or using a cryostat
Cryostat procedure
Tissue blocks can be frozen by adapting a conventional freezing microtome gas supply of carbon dioxide gas or using a cryostat
Mounting media
Synthetic water-soluble glycols and resins used for mounting tissue blocks for cryostat sectioning
Cryostat sections of fresh, unfixed tissue usually attach easily to the slide and preserve enzymes and other substances for histochemical studies
Examination of nerve and muscle
Muscle and nerve biopsies are divided into portions for formalin fixation, unfixed snap-freezing, resin embedding for EM, and biochemical studies
Freeze-drying
Rapid freezing of fresh tissue at -160°C, followed by removal of ice water molecules by sublimation in a vacuum chamber at -40°C, without chemical fixation
Freeze-drying
Particularly important for enzyme studies
Used for immunocytochemistry, fluorescent antibody studies, autoradiography, microspectrofluorimetry, and scanning electron microscopy
Freeze-substitution
Dehydration of rapidly frozen tissue at low temperatures to avoid ice crystal formation and damage
Freeze-substitution is similar to freeze-drying in preparing and preserving tissue blocks for subsequent sectioning