Forensic Medicine and Toxicology
Forensic Pathology: Death, Postmortem Changes and Autopsy
Forensic pathology for MBBS and NEET-PG: modes of death, rigor mortis and lividity timing, cadaveric spasm, putrefaction and the medico-legal autopsy, mapped to NMC codes FM2.1 to FM2.28.
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Forensic Pathology: Death, Postmortem Changes and Autopsy
Forensic pathology for MBBS and NEET-PG: modes of death, rigor mortis and lividity timing, cadaveric spasm, putrefaction and the medico-legal autopsy, mapped to NMC codes FM2.1 to FM2.28.
Forensic pathology is the core of the death investigation. This chapter covers the definitions and modes of death, the sequence and timing of postmortem changes used to estimate the time since death, and the aims and legal procedure of the medico-legal autopsy, including special situations such as custodial death, exhumation and infant death.
High-yield: Forensic Pathology: Death, Postmortem Changes and Autopsy
- Somatic death is the stopping of the heart, breathing and brain function, while molecular death is the death of individual tissues over the following hours.
- Brainstem death allows organ donation under the Transplantation of Human Organs and Tissues Act 1994.
- Algor mortis is cooling of the body; the rate is roughly 1 to 1.5 degrees Celsius per hour in temperate conditions but varies widely.
- Rigor mortis usually begins in 1 to 2 hours, is complete in about 12 hours, stays for 12 hours and passes off over the next 12 hours in Indian conditions.
- Cadaveric spasm is instant stiffening of a muscle group at the moment of death, needs no rigor to develop and cannot be reproduced artificially, so it is strong evidence of the last act.
- Postmortem lividity (hypostasis) begins within about 30 minutes to 2 hours and becomes fixed after 6 to 8 hours.
- Cherry-red lividity suggests carbon monoxide or cyanide poisoning, while brown lividity suggests methaemoglobinaemia.
- Putrefaction first shows as greenish discolouration over the right iliac fossa, usually within 12 to 24 hours in the tropics.
- Adipocere is the hydrolysis of body fat into a greasy waxy substance, favoured by moist surroundings and taking weeks to months.
- Mummification is drying and shrivelling of the body in hot dry or well-ventilated conditions.
- A medico-legal autopsy needs a police requisition and does not require the relatives' consent, unlike a clinical autopsy.
- The hydrostatic (lung float) test is used to decide whether a newborn breathed after birth, though it is not fully reliable on its own.
- Deaths in custody require videography and a panel autopsy in line with National Human Rights Commission guidelines.
- Exhumation in India is ordered by a magistrate and has no time limit after burial.
- Cyanosis, congestion, petechiae and fluidity of blood are the classical general signs of asphyxial death.
Timing of the early postmortem changes
- **Algor mortis:** Cooling of roughly 1 to 1.5 degrees Celsius per hour in temperate conditions; highly dependent on environment and body size.
- **Rigor mortis:** Onset 1 to 2 hours, complete about 12 hours, persists 12 hours, then passes off. Faster in warm climates.
- **Postmortem lividity:** Appears within 30 minutes to 2 hours, becomes fixed after 6 to 8 hours. Colour hints at cause.
- **Cadaveric spasm:** Instant, localised, cannot be faked. Records the deceased's last voluntary act.
NMC competencies in this chapter
- **FM2.1:** Death: definitions and types, somatic and molecular death
- **FM2.5:** Modes of death: coma, asphyxia and syncope
- **FM2.8:** Postmortem changes: cooling, lividity, rigor mortis and cadaveric spasm
- **FM2.9:** Putrefaction, mummification, adipocere and maceration
- **FM2.10:** Estimation of time since death
- **FM2.11:** Autopsy: types, aims and objectives
- **FM2.15:** Death in custody and NHRC guidelines
- **FM2.28:** Signs of live birth, viability, foetal age and the hydrostatic test
Frequently Asked Questions
Why is cadaveric spasm forensically important?
It fixes a muscle group in the position held at the instant of death and cannot be reproduced after death, so it can reveal whether a weapon was grasped voluntarily or placed later.
How is the time since death estimated?
By combining body temperature, rigor and lividity, the stage of putrefaction, stomach contents and entomology; no single sign is precise, so several are used together.
Does a medico-legal autopsy need family consent?
No. It is carried out on a police requisition in the public interest, unlike a clinical or academic autopsy which needs consent of the relatives.
What does cherry-red postmortem lividity suggest?
It points to carbon monoxide poisoning, and a similar bright colour can be seen in cyanide poisoning and in bodies exposed to cold.
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