Postmortem Lividity (Livor Mortis / Hypostasis)

Definition

Time Course

• Fixation was once thought to be due to blood coagulation - this is WRONG. Fixation occurs because:
  1. Blood is packed into toneless, distended capillaries and cannot flow
  2. Rigor mortis obliterates the large vessels, preventing blood resettlement
  3. Haemolysis causes haemoglobin to diffuse and stain surrounding tissues
  4. After full rigor, venules and capillaries are compressed
• Thumb blanch test: If pressure blanches the area → lividity not fixed → time since death < 8 hours. If no blanching → fixed → time since death > 6 hours.

Shifting and Fixation

• Complete shifting: If the body is moved before fixation (within ~6 hours), lividity disappears from the original area and reforms in the new dependent parts (secondary lividity). A slight residual stain remains in the original area from haemolytic tissue staining.
• Incomplete shifting: After body is turned, faint lividity appears in the new dependent parts while original areas retain most of their staining.
• After fixation (> 6-12 hours): Position of lividity is NOT significantly altered even if the body is moved - this is the key forensic use.

Distribution by Position of Body

• White band from tight collar/beaded threads mistaken for ligature strangulation
• Parallel marks on neck (head turned sideways) mistaken for manual strangulation
• Alternate dark/light stripes from lying on a crumpled blanket mistaken for bruises

Colour of Lividity and Its Cause-of-Death Significance

Lividity vs. Bruise (Table 11.1 - Parikh's)

Tip: If doubt exists or bruise is on a dependent part, cut into the suspect area and take a portion for histology.

Lividity vs. Congestion (Internal Organs) (Table 11.2 - Parikh's)

Factors Affecting Intensity

Medicolegal Importance (Exam Favourite)

1. Sign of death - reliable and objective.
2. Position of body at time of death - distribution indicates if body has been moved after death (e.g., murder and repositioning).
3. Time since death - early unfixed lividity vs. fixed lividity (blanch test).
4. Cause of death - colour of lividity (CO, cyanide, etc.).
5. Circumstances/mode of death - pattern in hanging, drowning, electrocution.

Special Points

• Isolated patches of lividity on front and sides of the neck (from incomplete emptying of external jugular/common facial veins) can be mistaken for throttling bruises (Gordon and Shapiro sign).
• In putrefaction, haemolysis causes lividity to shift upward (to head/neck) due to gas pressure - can be mistaken for violence. Colour changes: dusky → brown → green → disappears.
• In mummification, lividity turns brown to black due to desiccation.
• In cold/hypothermia, cherry red staining (similar to CO) can occur due to oxygenation of haemoglobin in skin capillaries.
• Frost erythema: red-purple spots over shoulder, knee, elbow from hypothermia can mimic hypostatic patches.
• Petechial haemorrhages in hypostatic areas are common in narcotic poisoning and acute cardiac arrest.
• Fixation occurs earlier in summer; delayed in asphyxial deaths and intracranial lesions.

Postmortem Lividity - Simplified 🩸

What is it? (1 line)

Blood pools in the lowest parts of a dead body due to gravity → causes skin discoloration.

Time Timeline (memorise these numbers)

1-3 hrs  → Mottled patches appear
3-6 hrs  → Patches join together
6-12 hrs → Fully developed & FIXED

• Presses thumb → skin goes white = NOT fixed = death < 8 hrs
• Presses thumb → skin stays coloured = FIXED = death > 6 hrs

Why does it Fix? (NOT due to clotting - common MCQ trap!)

1. Blood packed tightly in toneless capillaries - can't move
2. Rigor mortis blocks big vessels
3. Haemolysis stains surrounding tissue permanently

Colour in Poisoning - MEMORY TRICKS 🎨

The Big 3 (most asked in exams):

The Rest:

Quick Poem to remember CO, Cyanide, Chlorates:

"CO is Cherry, Cyanide is Pink, Chlorates are Chocolate - don't you think?"

Cherry Red = 3 causes (MCQ trap!)

1. Carbon monoxide
2. Exposure to cold
3. Burning (fire deaths)

Normal colours:

• Fresh: Bluish-pink
• Later: Bluish-purple
• Asphyxia: Intense purple (lots of deoxygenated blood)
• Anaemia/blood loss: Very faint

Lividity vs Bruise - Simple Version

Medicolegal Importance -5 Points (exam answer)

1. Sign of death
2. Position of body at time of death
3. Time since death (blanch test)
4. Cause of death (colour tells you the poison)
5. Circumstances of death (hanging, drowning pattern)

Special Patterns by Death Type

One Dangerous Mistake to Avoid

Isolated patches of lividity on the front and sides of the neck can look like bruises from throttling - do NOT confuse them!