Histopathology in Autopsies

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Intro & Role - Biopsy Bits & Bobs

  • Intro: Microscopic tissue exam; confirms gross, reveals subtle pathology. Key autopsy adjunct.
  • Role:
    • Clarify Cause of Death (e.g., early MI, myocarditis).
    • Time Since Death estimation: While histopathology can provide valuable information, the ability to accurately estimate TSD based solely on wound healing stages in post-mortem tissue is limited and often unreliable due to post-mortem changes like autolysis and putrefaction.
    • Identify occult disease (e.g., TB, tumors).
    • Differentiate ante-mortem vs. post-mortem injuries.
  • When to Sample (Biopsy Bits):
    • Routinely: Brain, Heart, Lungs, Liver, Kidneys (📌 B-HLLK).
    • Suspicious lesions, track marks, wound margins.
    • Sudden deaths (adult/infant), medical negligence allegations.
    • Gross findings equivocal/absent.
    • Preservative: 10% buffered formalin.

⭐ In cases of alleged medical negligence or custodial deaths under BNSS provisions, histopathology is mandatory to exclude or confirm natural disease contributing to death.

Collection & Fixation - Sample Secrets

  • Collection Strategy:
    • Samples: Lesion, normal, junction. Size: 1-2 $cm^2$, 3-5 mm thick.
    • Hollow viscera: All layers. Small organs (adrenals): Whole/bisected.
    • Brain: Suspend in formalin before slicing to prevent distortion.
    • Modern imaging (CT, MRI) guides precise sample localization for BSA evidence requirements.
  • Fixation Protocol:
    • Primary fixative: 10% buffered formalin; specialized fixatives for molecular studies.
    • Volume: Fixative 10-20x tissue volume. 📌 "Ten Times The Tissue."
    • Duration: 24-48 hrs (min 6 hrs) - varies by tissue type and downstream analysis.
    • Formalin pigment: Acidic artifact; remove with alcoholic picric acid.
  • Handling Essentials:
    • Avoid crush artifacts. Comprehensive documentation for BNSS chain of custody.
    • Special cases: Bouin's (testis, GI), Glutaraldehyde (EM), immunohistochemistry fixatives.

⭐ Inadequate fixation (too short, insufficient volume) is a common cause of non-diagnostic histopathology slides.

Processing & Stains - Stains & Stories

  • Tissue Processing: Fixation (10% NBF) → Dehydration (alcohols) → Clearing (xylene) → Wax Infiltration → Embedding → Sectioning (3-5 µm) → Staining.
  • Key Stains & Their Tales:
    • H&E (Hematoxylin & Eosin): Routine; nuclei (blue), cytoplasm/collagen (pink).
    • Prussian Blue: Iron (hemosiderin in old bruises).
    • PAS (Periodic Acid-Schiff): Glycogen, fungi, basement membranes.
    • Oil Red O / Sudan Black B: Lipids (fat embolism; requires frozen/fresh tissue).
    • Masson's Trichrome: Collagen (blue/green), muscle (red) - MI healing, fibrosis.
    • Congo Red: Amyloid (polarized light: apple-green birefringence).
    • Immunohistochemistry (IHC): Specific antigen-antibody reactions for cell markers.

⭐ For suspected fat embolism, Oil Red O or Sudan Black B on frozen sections are crucial as routine processing (alcohol, xylene) dissolves fat globules from tissues.

Key Forensic Findings - Microscopic Clues

Microscopy reveals cellular evidence for cause, manner, and time of death.

  • Myocardial Infarction (MI) Timing:

    • Modern Classification: Current forensic pathology recognizes Type 1 (spontaneous), Type 2 (secondary), and other MI classifications.
    • Timing Challenges: Precise histopathological timing requires clinical correlation and may be uncertain without acute coronary occlusion evidence.
    • General Pattern: Wavy fibers (early), coagulative necrosis (4-12h), neutrophil infiltration (12-24h), macrophages (1-3d), granulation tissue (3-7d), fibrous scar (>2wks).
  • Drowning:

    • Diatoms in distant organs (bone marrow, brain, kidney).
    • Lungs: edema, congestion, alveolar distension.
  • Asphyxia:

    • Lungs: congestion, edema, intra-alveolar hemorrhage.
  • Wound Vitality:

    • Inflammatory cells (neutrophils, macrophages) indicate vital reaction.
    • Absence of cellular reaction suggests post-mortem injury.
  • Poisons (Organ-specific changes):
    • Liver: Fatty change (e.g., alcohol, phosphorus), centrilobular necrosis (e.g., paracetamol).
    • Kidney: Acute tubular necrosis (e.g., heavy metals, ethylene glycol).
  • Electrocution:
    • Skin (electric mark): Streaming of nuclei, nuclear elongation.

⭐ Diatoms found in sealed organs like femur marrow, especially if species match the putative drowning water, are strong evidence of antemortem drowning.

  • H&E is routine stain; 10% formalin is standard fixative (tissue:formalin 1:10).
  • Determines time of injury/death, identifies microscopic pathology, detects occult disease.
  • Diagnoses MI changes (wavy fibers, neutrophils), drowning (diatoms), toxic effects.
  • Special stains (PAS, Perl's) aid when H&E is inconclusive.
  • Routine samples: heart, lungs, liver, kidneys, brain.
  • Vital in negative autopsies to find COD if gross findings are normal.
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Histopathology in Autopsies - Free Indian Medical PG Review