HISTOPATHOLOGY

Page 1: Histopathology Techniques

Histological Technique

  • Fixation: The preservation of tissue specimens for examination.

  • Dehydration: Removal of water from the tissue.

  • Clearing: Replacing dehydrating agents with clearing agents to facilitate infiltration.

  • Embedding: Infiltrating the tissue with a medium to allow cutting.

  • Cutting: Slicing the embedded tissue into thin sections.

  • Staining: Applying dyes to visualize tissue components.

Specimen Handling and Identification

  • Essential components of specimen container labels:

    • Patient’s name

    • Age or birth date

    • Medical record number

  • Labels must be attached firmly to the body of the container, not the lid.

Methods of Fresh Tissue Examination

  1. Teasing or Dissociation: Dissection of tissue in isotonic salt solution for microscopic examination.

  2. Squash Preparation: Forcing small tissue fragments (≤1mm) between slides for examination.

  3. Smear Preparation: Appropriate for cytological exams, especially for cancer diagnosis.

    • a. Streaking: Direct application for even distribution.

    • b. Spreading: Moderately thick films from mucous strands.

    • c. Pull-apart: Useful for thick secretions.

    • d. Touch Preparation: Impression smears to maintain cell relationships.

  4. Frozen Section: Quick diagnosis method using cryostat.

    • Applications include rapid pathologic diagnosis and immunohistochemical staining.

    • Freezing methods: Include liquid nitrogen and isopentane cooled by liquid nitrogen.

Processing of Tissues

  • Steps for solid tissue preservation and processing:

    1. Fixation

    2. Dehydration

    3. Clearing

    4. Infiltration

    5. Embedding

    6. Trimming

    7. Section cutting

    8. Staining

    9. Mounting

    10. Labeling

Histotechnology

  • Aim: To create microscopic preparations that represent the tissue structure in life and preserve tissue during fixation.

Page 2: Fixation in Histopathology

Fixation

  • The critical first step in histotechnology allows for proper tissue examination.

  • Quality of tissue fixation impacts slide section quality.

  • Fixation prevents:

    • Degeneration and decomposition

    • Distortion of tissue structure

    • Break down of cells

Basic Mechanisms of Fixation

  1. Additive Fixation: E.g., formalin; adds to cells without volatilization.

  2. Non-additive Fixation: E.g., alcoholic fixatives; removes water without adding chemicals.

Main Factors in Fixation

  1. pH: Optimal between 6 and 8.

  2. Temperature: Room temperature is standard, but may vary.

  3. Thickness of Sections: Affects penetration of fixatives.

  4. Osmolality: Best with slightly hypertonic solutions.

  5. Concentration: Commonly 10% formaldehyde.

  6. Duration of Fixation: Critical for preventing tissue damage.

Practical Considerations of Fixation

  1. Penetration: Varies; formalin penetrates 1 mm/hour.

  2. Volume: Fixative volume should be 10-25x tissue volume.

  3. Duration of Fixation: Can be reduced using heat or agitation.

Types of Fixatives

According to Composition

  • Simple Fixatives: One component (e.g., formaldehyde).

  • Compound Fixatives: Two or more fixatives.

According to Action

  • Microanatomical Fixatives: Preserves cell structures without alteration.

  • Histochemical Fixatives: Stabilizes chemical constituents in cells.

Types of Cytological Fixatives

  1. Nuclear Fixatives: Often contain glacial acetic acid.

  2. Cytoplasmic Fixatives: Should not contain glacial acetic acid.

  3. Histochemical Fixatives: Preserve chemical constituents without losing structure.

Page 3: Physical and Chemical Methods of Fixation

Physical Methods

  1. Heat Fixation: Accelerates fixation and tissue processing.

  2. Microwave Heating: Reduces fixation time significantly.

  3. Freeze-Drying and Freeze Substitution: Preserves delicate structures.

Chemical Methods

Coagulant Fixatives

  • Dehydrant Coagulant Fixatives: Alcohol and acetone; denatures proteins.

  • Acidic Coagulants: E.g., acetic acid or picric acid; brightens stain but can hydrolyze nucleic acids.

Aldehyde Fixatives

  • Formaldehyde: Most commonly used; 10% solution is recommended.

    • Precautions: Low temperatures may cause turbidity; concentrated solutions must not be neutralized.

  • Formol-Saline: Used for CNS tissues; retains histochemical properties.

  • Neutral Buffered Formalin: Recommended for surgical specimens; preserves well at pH 7.

Glutaraldehyde**: Recommended for electron microscopy; varying concentrations based on tissue size.

Metallic Fixatives

  1. Mercuric Chloride: Provides good preservation; requires fresh preparation.

  2. Chromate Fixatives: Potassium dichromate; preserves lipids, but does not preserve cytoplasmic structures.

Picric Acid Fixatives**: Used for specific tissues, e.g., Bouin's solution for embryos.

Alcohol Fixatives**: Primarily for smears and urgent biopsies.

Page 4: Specialized Fixatives

Zenker's Fluid

  • General fixative for various tissues; excellent staining results.

Zenker-Formol Fluid

  • Used for pituitary and hematopoietic tissues; high preservation quality.

Heidenhain’s Susa Solution

  • Particularly used for biopsy specimens; retains cellular structure.

B-5 Fixative

  • Ideal for bone marrow biopsies; gives rapid fixation but should be freshly made.

Chromate Fixatives

  • Potassium Dichromate: Preserves certain cellular structures effectively.

Regnaud's Fluid

  • Effective for histological examination of cellular components.

Lead Fixatives

  • Useful for specific cytological examinations; care needed due to toxicity.

Alcoholic Fixatives

  • Various types with specifications according to the tissues being fixed.

Practical Considerations

  • Freshly prepared solutions are pivotal for effective histopathological work.

Page 5: Dehydration Process

Dehydration

  • Key for preparing tissue for embedding post-fixation.

  • Removes water using increasing concentrations of alcohol.

  • General rule: Use at least 10 times the volume of tissue.

Characteristics of Dehydrating Agents

  1. Rapid dehydration without excessive shrinkage.

  2. Slow evaporation rates.

  3. Effective on fatty tissues.

  4. Non-toxic and non-flammable.

Common Dehydrating Agents

  • Alcohol: Most common; varies in concentration.

  • Acetone: Quick-acting; less used for routine purposes.

  • Dioxane: Good for minimal distortion.

Specific Alcohol Types

  1. Ethyl Alcohol: Widely used for routine dehydration.

  2. Methyl Alcohol: Toxic; specific applications only.

  3. Butyl Alcohol: Slower dehydration; used when shrinkage must be minimized.

Page 6: Clearing Process

Clearing (De-alcoholization)

  • Removing dehydrating agents and making tissues translucent.

  • Clearing agents should mix well with paraffin wax; provide transparency due to refraction index.

Characteristics of Good Clearing Agents

  1. Miscible with alcohol for effective removal.

  2. Easily removed by embedding medium.

  3. Non-damaging to tissue structure.

  4. Not evaporative or toxic.

Common Clearing Agents

  1. Xylene: Most commonly used; inexpensive.

  2. Toluene: Substitute; moderately priced.

  3. Benzene: Fast action; caution due to health implications.

  4. Chloroform: Can denote more substantial tissue but is toxic.

  5. Cedarwood Oil: Least distortion, recommended for delicate specimens.

Page 7: Impregnation and Embedding

Impregnation

  • Replacing clearing agents with embedding substances.

Embedding Media

  1. Paraffin Wax: Most common and effective for routine processing.

    • Must be maintained at proper temperatures to avoid tissue damage.

  2. Celloidin: For delicate specimens.

  3. Gelatin: Used when dehydration needs to be avoided.

Orientation in Embedding

  • Arranging tissue correctly for proper sectioning and analysis.

Types of Molds

  1. Leuckhart’s Embedding Mold: Basic form.

  2. Compound Embedding Units: Multiple compartments for different samples.

  3. Plastic Embedding Rings: Often preferred for ease of use.

Page 8: Microtome and Its Types

Microtomy Process

  • Cutting tissue into uniform sections for microscopic examination.

Microtome Parts

  1. Block Holder: Holds tissue securely.

  2. Knife Carrier: For cutting.

  3. Feed Mechanism: Ensures even, minute movements for uniform cutting.

Microtome Types

  1. Rocking Microtome: Suitable for various tissue blocks.

  2. Rotary Microtome: Most common for routine laboratory use.

  3. Sliding Microtome: For harder tissues; more dangerous.

  4. Freezing Microtome: For quick diagnosis and sensitive tissues.

  5. Ultrathin Microtome: For electron microscopy, cutting at 0.5 μm.

Care of Microtome

  • Regular cleaning and maintenance required to ensure quality sections.

Page 9: Knife Preparation and Use

Microtome Knives

  1. Plane-Concave Knife: Commonly used for general slicing.

  2. Plane-Wedge Knife: Longer; used particularly for tough specimens.

Honing and Stropping

  • Sharpening involves two stages: honing for shaping, stropping for polishing.

Honing Precautions

  • Use proper technique and materials to maintain knife edges.

Disposable and Specialized Knives

  • Disposable blades, glass knives, and diamond knives each have specific applications tailored to the expected conditions of use.

Page 10: Staining Techniques in Histopathology

General Staining Process

  • Applying dyes helps visualize tissue architecture and cellular morphology.

Types of Stains

  1. Histological Staining: Shows tissue relationships and cellular composition.

  2. Histochemical Staining: For chemical localization within tissues.

  3. Immunohistochemical Staining: Combo of immunologic and histochemical techniques for antigen detection.

Techniques in Staining

  • Direct Staining: Using dye directly on the sample.

  • Indirect Staining: Involves mordants and enhances the staining process.

Staining Categories

  • Counterstaining: Adding a different color for contrast;

  • Metachromatic Staining: For differentiation of substances by differing colors.

  • Progressive vs. Regressive Staining: Techniques depend on desired staining intensity and detail retention.

Page 11: Specialized Staining Techniques

Counterstaining and Metallic Impregnation

  • Enhances visibility of certain cellular components.

  • Metallic salts can provide opaque contrasts to samples.

Vital Staining Techniques

  • Demonstration of cellular activities and living cell interactions.

Staining of Paraffin Sections

  • Specific techniques required to prepare paraffin sections for optimal staining effectiveness.

Routine H&E Staining

  • Most utilized method for microanatomical studies, employs both dyes for nuclear and cytoplasmic visualization.

Page 12: Additional Staining Methods

Eye Drop Method for Frozen Sections

  • Quick methods for staining; effective for rapid preparations.

Papanicolau Method in Gynecological Cytology

  • Three main steps to ensure proper smearing and recognition of cellular morphology.

  • Aids in identifying abnormalities in cervical cells.

Bethesda System for Specimen Adequacy

  • Evaluation categories ensure quality control in specimen collection and processing.

Page 13: Cytology Techniques

Exfoliative vs. FNA Cytology

  • Distinguishing between two primary cytological methods used for diagnosis.

Applications of Exfoliative Cytology

  • Screening for malignancy and assessing hormonal function through cytological examination of various fluids.

Cytology: Fixation

  • Essential for optimal preservation of cell structure in the diagnostic process.

  • Methods include 95% ethanol or ether mixtures.

Gynecological Cytology: Liquid-Based Preparations

  • Improved methods for diagnostic reliability.

Page 14: Papanicolau Staining Technique

Steps in Staining Technique

  1. Fixation

  2. Staining and Differentiation

  3. Counterstaining

  4. Dehydration and clearing

Bethesda System Categories for Evaluation

  • Ensures quality in gynecological samples and identifies inadequacies.

Page 15: Fine Needle Aspiration Cytology

FNA Technique

  • Use of specific needle gauges for effective aspiration.

  • Preparing slides immediately from aspirate.

Importance in Diagnostic Cytology

  • Fast and efficient technique for various tissue samples.

Page 16: Cellular Responses to Injury

Homeostasis and Cellular Injury

  • Key concepts in understanding cell functionality under distress.

Causes of Cell Injury

  • Various physical, chemical, and biological factors affecting cellular integrity.

Principal Patterns of Cell Death

  1. Necrosis: Uncontrolled cell death with tissue response.

  2. Apoptosis: Programmed cell death.

Page 17: Cellular Adaptations

Forms of Cellular Adaptation

  1. ** Hyperplasia**: Increase in cell number.

  2. Hypertrophy: Increase in cell size.

  3. Atrophy: Decrease in size/function.

  4. Metaplasia: One cell type replaced by another.

Mechanisms of Adaptation

  • Adaptive responses affected by environmental changes, influencing cellular behavior.

Page 18: Atrophy and Hyperplasia

Physiologic and Pathologic Atrophy

  • Examples of causes and effects that lead to cell shrinkage.

Hyperplasia Types

  • Hormonal and compensatory factors influencing cell proliferation.

Page 19: Intracellular Accumulation

Types of Cellular Accumulations

  • Normal substances and abnormal accumulations impacting cell functionality.

Fatty Change Examples

  • Conditions leading to excessive lipid production in cells.

Page 20: Pigmentation and New Growth

Pigments in Pathology

  • Types of endogenous and exogenous pigments effecting tissue appearance and function.

Neoplasia Overview

  • Definitions of neoplasms, benign and malignant tumors, and associated terminology.