Paraffin Sections

Paraffin sectioning is a widely used histological technique for preparing tissue samples for microscopic examination. It involves the embedding of biological tissues in paraffin wax, allowing for thin sectioning of the tissue with minimal damage to its morphology. Paraffin sections are critical in diagnostic pathology and research, offering a robust method for preserving tissue architecture and cellular detail.

Technical Process of Paraffin Sections

The preparation of paraffin sections follows a multi-step process, including fixation, dehydration, embedding, sectioning, and staining. Each step is essential to maintaining the integrity of the tissue for accurate histopathological examination.

• Fixation: The first step involves fixing the tissue in a formaldehyde-based solution, typically 10% neutral-buffered formalin (NBF). Fixation preserves tissue structure by cross-linking proteins, preventing autolysis and microbial growth. Proper fixation is critical to maintaining cellular morphology and antigenicity for downstream staining procedures.
• Dehydration: After fixation, the tissue undergoes dehydration, usually through a graded series of ethanol solutions. Dehydration removes water from the tissue, which is necessary because paraffin wax is hydrophobic and incompatible with water.
• Clearing: The dehydrated tissue is cleared using an organic solvent like xylene. This step removes any remaining ethanol and ensures that the tissue is fully compatible with paraffin wax. Xylene replaces the ethanol in the tissue, making it easier for the paraffin to infiltrate the sample.
• Paraffin Embedding: The cleared tissue is then infiltrated with molten paraffin wax at approximately 60°C. This step allows the tissue to harden as the paraffin cools, preserving its structure and making it suitable for sectioning. The tissue is embedded in a block of paraffin, with proper orientation crucial for accurate sectioning.

Clinical and Research Applications

Paraffin sections are utilized extensively in both clinical and research settings due to their versatility and ability to preserve tissue for detailed analysis.

• Oncological Diagnosis: Paraffin sections are essential for diagnosing cancers. Tumor samples are routinely processed in paraffin for histopathological evaluation, grading, and staging. The precise cellular detail and tissue architecture preserved in paraffin sections allow pathologists to assess tumor margins, invasion patterns, and lymph node involvement.
• Immunohistochemistry: Paraffin sections are widely used in IHC, where antibodies are applied to detect specific proteins or antigens. This technique is critical for determining the expression of biomarkers in cancer, inflammatory diseases, and infections. Paraffin sections provide stable material for multiple rounds of staining and analysis.
• Molecular Pathology: Paraffin sections can also be used for molecular techniques such as in situ hybridization (ISH) or fluorescence in situ hybridization (FISH), enabling the visualization of specific DNA or RNA sequences within the preserved tissue.

Paraffin sectioning is a critical technique in both diagnostic pathology and biomedical research, offering precise tissue preservation for histological and molecular analysis. While it requires more time than other methods like frozen sections, its ability to maintain tissue integrity and support a variety of staining methods makes it indispensable for comprehensive tissue evaluation.