Pathological Sciences: Tissue Processing Lecture 3

Tissue Processing Steps

• After fixation, the next step is dehydration in routine tissue processing.
• The first step from specimen to report is fixation.
• Following impregnation in tissue processing, the embedding step occurs.
• The last step in routine tissue processing is microtomy, where tissue is sliced for examination.

Paraffin Technique and Its Purpose

• The aim of the Paraffin Technique is to preserve histological architecture for accurate microscopic analysis.
• Paraffin wax is the embedding medium of choice for routine specimens due to its ability to infiltrate tissue thoroughly.

Instruments and Reagents

• A microtome is the instrument used for cutting formalin-fixed paraffin-embedded (FFPE) blocks.
• Industrial methylated spirit (IMS) is commonly used as a dehydrating solution, but its main drawback is toxicity.
• Clearing reagents, such as xylene, are used to remove alcohol from tissue before embedding; alternatives to xylene include limonene and other solvents.

Handling and Validation

• If xylene waste is produced, it should be disposed of according to hazardous waste regulations to prevent environmental harm.
• Tissue processing schedules must be validated to ensure optimal outcomes through consistent methodologies.

Fatty Tissue Processing

• Processing fatty tissues requires specialized techniques due to their unique composition, which may involve additional embedding agents.

Quality Assurance

• Block checking is essential in the quality assurance process, ensuring that adequate samples are prepared for diagnostics.
• The intermediary steps in paraffin processing play a critical role in ensuring the tissue is properly prepared for embedding, enhancing preservation quality.

Characteristics and Effects

• The characteristics of paraffin wax, such as melting point, clarity, and compatibility with staining techniques, make it highly suitable for tissue processing.
• Insufficient fixation and formalin penetration can lead to poor tissue preservation, resulting in artifact formation and diagnostic challenges.

Sections and Thickness

• The typical thickness of routine sections in microtomy is around 4 to 5 micrometers.

Cold Plates and Hard Tissue

• The aim of using a cold plate in the tissue embedding process is to facilitate rapid solidification of the embedding medium, improving morphology preservation.
• Hard tissue pre-treatment is vital for ensuring complete infiltration of the embedding medium, especially for denser tissues.

Automation in Processing

• Advances in automation have increased the capability for processing larger tissue blocks, helping meet the growing demands for laboratory reporting.