EXAMINATION OF FRESH TISSUE

• Histology


  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