PRESERVATION OF VISCERA FOR CHEMICAL AND HISTOPATHOLOGICAL EXAMINATION

The preservation of viscera is a critical step in forensic science and medical diagnostics, ensuring that vital tissues remain intact and unaltered for subsequent chemical and histopathological examinations. These examinations are instrumental in determining the cause of death, identifying the presence of toxins or drugs, and revealing microscopic changes indicative of disease or injury. Proper preservation techniques are paramount to prevent degradation, contamination, and autolysis, which can compromise the integrity of the evidence and lead to inaccurate conclusions.

Chemical Examination of Viscera

Chemical examination of viscera aims to identify and quantify the presence of exogenous substances, such as drugs, poisons, and their metabolites, as well as endogenous substances that may be altered in pathological conditions. The process begins with the careful collection and segregation of appropriate tissue samples.

A. Sample Collection and Handling:

1. Selection of Viscera: Generally, a representative selection of organs is collected, including the liver, kidneys, brain, lungs, stomach, intestines, urine, bile, and blood. The specific organs chosen may depend on the suspected mode of death, the route of administration of a substance, or the clinical presentation. For instance, if a poison is suspected to have been ingested, the stomach and its contents are of primary importance. If intravenous drug use is suspected, blood and injection site tissues are crucial.
2. Gross Examination and Documentation: Before preservation, a thorough gross examination of each organ is performed. Any abnormalities, such as discoloration, lesions, or foreign bodies, are meticulously documented. Photographs are taken to record the gross appearance.
3. Sampling Strategy: For chemical analysis, small, representative portions of each organ are excised. These samples should ideally be taken from different areas of the organ to account for potential localized distribution of substances. For example, in cases of suspected alcohol poisoning, blood is collected from multiple sites if possible, and liver samples are taken from different lobes.
4. Segregation of Samples: It is crucial to keep samples for chemical analysis separate from those intended for histopathology. This prevents cross-contamination. Each sample should be placed in a clean, sterile, and appropriately labeled container. The labeling must include essential information such as case number, date and time of collection, name of the deceased, specific organ or body fluid, and the name of the person collecting the sample.
5. Packaging and Sealing: Containers are typically made of glass or inert plastic. They should be sealed to prevent leakage and contamination during transport and storage. Forensic evidence tape is often used to secure the seals, providing an unbroken chain of custody.

B. Preservation Techniques for Chemical Analysis:

The choice of preservation method depends on the type of chemical analysis to be performed and the analytes of interest. It is often beneficial to utilize multiple preservation methods for different analyses.

1. Refrigeration: For some analyses, particularly those involving volatile substances or enzymes, refrigeration at 4°C is the preferred method. This slows down the rate of decomposition and enzymatic activity without significantly altering the concentration of many analytes. Refrigeration is often used for blood, urine, and vitreous humor samples. However, prolonged refrigeration can still lead to some degradation of certain compounds.
2. Freezing: Freezing at -20°C or below is another common method for preserving samples intended for chemical analysis. This significantly halts enzymatic activity and bacterial growth, preserving a wider range of analytes for longer periods. Freezing is particularly useful for drugs, metabolites, and organic compounds. However, repeated freeze-thaw cycles can degrade some analytes and affect protein structure.
3. Chemical Fixation for Specific Analyses: In some instances, specific chemical fixatives are used to preserve certain analytes while rendering them unsuitable for others.
   • Ethanol (Alcohol): For the analysis of ethanol in body fluids, adding a known concentration of an alcohol (e.g., absolute ethanol) to the sample helps to prevent further fermentation by microorganisms and preserves the ethanol concentration. This is crucial for determining blood alcohol levels accurately.
   • Sodium Fluoride/Potassium Oxalate (Anticoagulant and Antiglycolytic): This mixture is commonly used for blood samples intended for glucose analysis. Sodium fluoride acts as an antiglycolytic agent, preventing the breakdown of glucose by red blood cells, while potassium oxalate serves as an anticoagulant.
4. Dried Deposits: For certain trace substances or drugs, allowing a small amount of blood or other fluid to dry on a sterile surface (e.g., filter paper or a clean glass slide) can be an effective preservation method. These dried deposits can be stored at room temperature and later eluted for analysis.

Histopathological Examination of Viscera

Histopathological examination involves the microscopic study of tissue structure to identify cellular abnormalities, pathological changes, and the presence of disease processes. The primary goal of preservation for histopathology is to maintain the tissue architecture and cellular morphology as close to the living state as possible.

A. Sample Collection and Handling for Histopathology:

1. Selection of Viscera: Similar to chemical analysis, a systematic approach to organ selection is essential. Large organs like the liver, spleen, and lungs might be sampled from multiple sites. For smaller organs, the entire organ might be submitted.
2. Gross Examination and Documentation: A detailed gross description of the organ, including its size, weight, color, consistency, and any visible lesions, is recorded. Photographs are taken.
3. Sampling Strategy for Histopathology: Representative sections of approximately 1-2 cm thickness are taken. Care should be taken to include any visible abnormalities or lesions. If an entire organ is too large to be effectively fixed, it should be incised to allow penetration of the fixative. However, excessive cutting can distort the tissue.
4. Immediate Fixation: The key principle in histopathology is rapid and efficient fixation. Tissues begin to autolyze (self-digest) immediately after cessation of blood supply. Therefore, fixation should commence as soon as possible after death or tissue removal.

B. Preservation Techniques for Histopathology:

The cornerstone of histopathological preservation is chemical fixation.

1. Fixation: Fixation is a process that stabilizes tissue components by forming chemical cross-links, preventing autolysis and putrefaction, and preserving cellular structures for microscopic examination.
   • Definition: Fixation is the process of preserving tissue structure and cellular morphology by preventing autolysis and putrefaction.
   • Mechanism: Fixatives typically work by cross-linking proteins within the cells and extracellular matrix, thereby creating a stable, insoluble network. This process also denatures enzymes that would otherwise degrade the tissue.
   • Ideal Fixative Properties: An ideal fixative should:
     • Penetrate tissues rapidly and evenly.
     • Preserve morphology accurately.
     • Not cause excessive shrinkage or distortion.
     • Not interfere with subsequent staining procedures.
     • Be relatively inexpensive and safe to handle.
     • Be stable for storage.
   • Common Fixatives:
     • Formalin (10% Neutral Buffered Formalin – NBF): This is the most widely used fixative in histology. It is a 10% solution of formaldehyde in a buffer, typically containing sodium phosphate. The buffering helps to maintain a neutral pH, preventing tissue damage that can occur with unbuffered formalin, which can become acidic. Formaldehyde works by cross-linking amino groups in proteins, forming methylene bridges. It penetrates tissues relatively quickly and preserves cellular detail well, although it can cause some hardening.
       • Mechanism: Formaldehyde reacts with the -NH₂ groups of proteins, forming methylene bridges (-CH₂-) that link protein molecules together. This stabilizes the tissue structure. It also reacts with amines, amides, and other organic molecules.
       • Penetration: Formaldehyde penetrates tissues at a rate of about 1 mm per hour. Therefore, samples for histopathology should not be excessively thick (ideally < 0.5 cm).
       • Advantages: Widely available, inexpensive, good general-purpose fixative, preserves most cellular components.
       • Disadvantages: Can cause tissue hardening, potential carcinogen, can be irritating to skin and respiratory system, may not preserve certain antigens for immunohistochemistry as well as other fixatives.
       • Usage: Typically used at room temperature. The volume of fixative should be at least 10-20 times the volume of the tissue.
     • Alcohol (Ethanol/Methanol): Alcohols primarily denature proteins through coagulation, rather than cross-linking. They are effective fixatives for certain applications, particularly for preserving glycogen and for some cytological preparations. However, they can cause significant shrinkage and distortion of tissue architecture compared to formalin.
       • Mechanism: Alcohols cause proteins to precipitate by reducing their solubility, disrupting hydrogen bonds and hydrophobic interactions.
       • Advantages: Good at preserving glycogen, can be used for rapid fixation, useful for certain staining techniques.
       • Disadvantages: Significant tissue shrinkage and distortion, can harden tissues, less effective at preserving fine structural details compared to formalin.
       • Usage: Typically used as 70-95% solutions.
     • Zenker’s Fluid (Mercuric Chloride, Potassium Dichromate, Acetic Acid): A classic fixative that provides excellent preservation of nuclear detail. However, mercuric chloride is highly toxic and leaves deposits that must be removed (mercuric pigment removal) before staining. It is less commonly used now due to toxicity concerns.
       • Mechanism: Mercuric chloride precipitates proteins and the dichromate oxidizes. Acetic acid helps to maintain nuclear detail.
       • Advantages: Excellent nuclear detail preservation.
       • Disadvantages: Toxic, leaves mercuric pigment, can cause brittleness, not suitable for routine use.
     • Bouin’s Solution (Picric Acid, Formaldehyde, Acetic Acid): This fixative provides excellent preservation of morphology, especially for endocrine tissues and spermatozoa. Picric acid, a strong dehydrating agent and protein precipitant, helps to minimize shrinkage.
       • Mechanism: Picric acid precipitates proteins and dehydrates tissue, while formaldehyde cross-links and acetic acid maintains nuclear detail.
       • Advantages: Minimizes shrinkage, excellent preservation of nuclei and cytoplasm, good for delicate tissues.
       • Disadvantages: Tissues are stained yellow by picric acid, which needs to be removed before staining. Picric acid is explosive when dry.
2. Tissue Processing: After fixation, tissues undergo processing to embed them in a solid medium for sectioning.
   • Dehydration: Tissues are gradually passed through increasing concentrations of alcohol (e.g., 70%, 80%, 95%, absolute ethanol) to remove water, which is immiscible with embedding media.
   • Clearing: The alcohol is then replaced with a clearing agent, such as xylene or toluene, which is miscible with both alcohol and the embedding medium. This step makes the tissue transparent.
   • Infiltration: The clearing agent is then replaced with molten paraffin wax. The wax infiltrates the tissue spaces.
   • Embedding: The infiltrated tissue is placed in a mold and surrounded by molten paraffin wax, which is then allowed to solidify, forming a solid block.
3. Sectioning (Microtomy): The paraffin block is then cut into extremely thin sections (typically 3-5 µm thick) using a microtome.
4. Staining: The thin sections are mounted on glass slides and stained to visualize cellular structures. Hematoxylin and eosin (H&E) is the most common stain, with hematoxylin staining nuclei blue and eosin staining cytoplasm and extracellular matrix pink. Special stains can be used to highlight specific cellular components or pathological processes.

Preservatives Used in Mortuary

In a mortuary setting, the primary goal of preservation is to slow down the decomposition process, preserving the body for identification, forensic examination, and eventual funeral arrangements. The methods and agents used differ from those for specific laboratory examinations, being more focused on overall gross preservation.

1. Refrigeration: This is the most common and effective method for short-term preservation of bodies in a mortuary. Refrigeration units designed for bodies (mortuary refrigerators or cold rooms) maintain a temperature of 2-4°C. This significantly retards bacterial growth and enzymatic activity, slowing down decomposition and allowing time for investigations or identification.
   • Mechanism: Low temperatures inhibit the growth and metabolic activity of putrefactive bacteria and reduce the rate of endogenous enzymatic breakdown of tissues.
   • Limitations: Refrigeration does not stop decomposition entirely, but rather slows it down. It is a temporary measure. It can also lead to some tissue changes, such as ice crystal formation if temperatures drop too low and can make tissues appear blanched.
2. Embalming: Embalming is a more invasive process used for longer-term preservation, particularly when the body is to be displayed or transported over long distances, or when refrigeration is not feasible. It involves the injection of a chemical solution into the vascular system and body cavities.
   • Embalming Fluids: These are complex chemical mixtures, with the primary active ingredient being formaldehyde (often in the form of formalin or paraformaldehyde). Other components include:
     • Alcohols (Methanol, Ethanol): Act as disinfectants and dehydrants.
     • Glycerol: Acts as a plasticizer, preventing tissues from becoming too brittle.
     • Anticoagulants (e.g., sodium citrate): To prevent blood clotting during injection.
     • Buffers: To maintain pH.
     • Dyes: To restore a more natural color to the skin.
     • Preservatives/Antiseptics (e.g., phenol, thymol): To kill bacteria and fungi and prevent further decomposition.
   • Mechanism of Embalming:
     • Fixation: Formaldehyde cross-links proteins in the tissues, making them resistant to bacterial and enzymatic degradation.
     • Disinfection: The chemicals in the embalming fluid kill microorganisms present in the body.
     • Dehydration: Some components help to remove excess tissue fluid, making the tissues firmer and less susceptible to decomposition.
     • Plastination: Glycerol and other plasticizers help to maintain a degree of suppleness in the tissues.
   • Cavity Treatment: In addition to arterial embalming, a more concentrated embalming fluid (cavity fluid) is often injected directly into the body cavities (thoracic, abdominal, pelvic) to disinfect and preserve the organs within.
3. Storage in Chemicals: In specific forensic contexts, and particularly for skeletal remains or mummified tissues, storage in solutions of certain chemicals can be employed for long-term preservation. This is less common for whole bodies.
   • Ethanol: Immersion in ethanol can preserve tissues and prevent decomposition for extended periods.
   • Formalin: While used for fixation, prolonged immersion in formalin can also act as a preservative for whole specimens, though it can cause tissue hardening.

Chain of Custody and Documentation

Regardless of the preservation method employed, maintaining a rigorous chain of custody and meticulous documentation is paramount. Every step, from sample collection to final analysis and disposal, must be recorded. This includes:

• Unique Case Identification: Each case must have a unique identifier.
• Detailed Sample Description: Clear labeling of each sample with its origin, date, time, and collector.
• Chain of Custody Log: A record of every person who handles the sample, including dates and times of transfer.
• Preservation Method Used: Documenting the specific fixative or storage condition applied.
• Chain of Custody for Embalming: For embalmed bodies, documentation of the embalming process, fluids used, and personnel involved is essential.

Conclusion

The preservation of viscera for chemical and histopathological examination requires distinct approaches tailored to the specific analytical goals. Chemical analysis prioritizes preserving the integrity of analytes, often utilizing refrigeration, freezing, or specific chemical additions. Histopathology demands the preservation of tissue architecture and cellular detail, with chemical fixation, primarily using formalin, being the cornerstone. In the mortuary, preservation focuses on slowing decomposition for identification and examination, with refrigeration being standard and embalming offering longer-term stabilization. Regardless of the specific application, meticulous handling, appropriate preservation techniques, and an unbroken chain of custody are fundamental to ensuring the accuracy and reliability of subsequent scientific investigations.

References:

• General Forensic Science:
  • Svensson, C., de Kinderen, P. J., & Mårtensson, L. (2017). Forensic Toxicology: Principles and Practice. Academic Press.
  • Taylor, D. J., Palmer, P. J., & Dennis, P. J. (2017). Taylor’s Encyclopedia of Clinical Laboratory Tests. F.A. Davis.
• Histopathology and Fixation:
  • Bancroft, J. D., Stevens, A., & Turner, D. R. (2013). Theory and Practice of Histological Techniques. Churchill Livingstone.
  • Böck, P. (2003). The Science of Microscopy: Optical and Maintenance. John Wiley & Sons.
  • Carleton, H. M., & Short, R. H. D. (1938). Histological Technique. Oxford University Press. (Older but foundational texts often provide detailed historical context on fixatives).
  • Suvarna, S. K., Layton, C., & Walter, P. (2018). A Colour Atlas of Histology. CRC Press.
• Mortuary and Embalming:
  • Erickson, C. W. (2019). Embalming Procedures: A Comprehensive Guide. C.B.C. Publishing.
  • Spitz, W. U., & Fisher, R. S. (2006). Medicolegal Investigation of Death: Guidelines for the Application of Pathology to Crime Investigation. Charles C Thomas Publisher.
  • Waller, J. (2017). The Science of Death: From Forensics to the Funeral. Icon Books.
• Chemical Analysis and Preservation:
  • Baselt, R. C. (2014). Disposition of Toxic Drugs and Chemicals in the Forensic Context. Biomedical Publications.
  • Kaye, S., & Cairns, E. R. (2015). Forensic and Clinical Applications of Chemical Tests. CRC Press.